Starting pathology (entire handbook)

Author: Mikael Häggström

Using this handbook

The goal of this handbook is to make a new pathology trainee able to properly handle at least 80% of cases that are expected at an average general pathology department, including the exclusion of the most pertinent differential diagnoses thereof.

It is recommended to scroll quickly through this handbook to get an idea of its content, and then keeping it at a known location for whenever information is needed for a corresponding patient case. It is not recommended to memorize its content indiscriminately. Other doctors and even laypersons can look up diseases and conditions themselves, including pathology characteristics, without the need for a pathologist consultation, so the expertise of memorizing such readily available information is expendable. In a world where diseases and conditions can readily be looked up, a major skill that distinguishes a pathologist from any person with Internet access is mainly the ability to identify and put words to findings on microscopy or other non-written results. Another major skill is to be able to deal with unusual or equivocal presentations. Unusual or equivocal presentations of very common diseases and conditions are still generally more common than rare diseases, and constitutes a major workload in everyday pathology practice. However, most textbooks still give disproportionately large room for rare diseases compared to such presentations. Nevertheless, strive to master the common conditions (including the most common pitfalls) before diving into the uncommon. Specialists and subspecialists may already have learned the common conditions, at least in their subspecialty, and they will often distract you from this pursuit by presenting rare conditions to you, because that is interesting to them, but do not spend excessive time or mental effort on such rare conditions during your first years.

What a pathologist needs to memorize

The best method for memorization is generally through repeated exposure in everyday practice, but the following things are most important for a pathologist to focus on memorizing:

• Emergent pathology, mostly relating to intraoperative or frozen section consultations. This includes information that usually cannot be timely looked up on the Internet when needed.
• Main pitfalls: Most common and dangerous situations where a pathologist may not recognize the need to look something up further or ask a senior colleague.
• Patterns and signs which can be seen grossly or under the microscope. It confers the ability to translate visuals into words that can be looked up if needed.
• Knowledge of where to find information for various situations. It includes which person or which search engine is most useful for various clinical situations. Google is generally an appropriate search engine, but sometimes more specific or comprehensive databases are necessary, such as for example ClinVar to look up the pathogenicity of specific genetic variants. The chapter will include a directory of major databases and external guidelines.
• Proficiency in diagnosing equivocal or borderline cases where readily available sources and evidence usually deal with discrete and specific disease entities and subcategories thereof.  Thus, in the question sections, many questions will be in the format of displaying readily available facts about diseases, including their typical immunohistochemistry patterns, but with equivocal or borderline case presentations.
• Having an idea of one’s unknowns; being aware of unfamiliar fields. For example, a pathologist generally does not need in depth knowledge about cases that are generally sent out to specialized centers (such as pediatric musculoskeletal oncology), as long as that pathologist is aware of lack of knowledge in that field.

• Dealing with Internet denialists and their exams. With the ease of access to pathology information on the Internet through smartphones and computers, those studying to for everyday practice as a pathologists should not spend time memorizing what can essentially always be conveniently and timely be looked up in times of need. The topics listed above are already immense enough to cover a lifetime of learning. Nevertheless, the path to pathology certification includes one or more exams, whose questions are largely made up of people who still do not acknowledge the access to the Internet in everyday pathology practice, and therefore this curriculum also includes this chapter.

Emergent pathology

Surprise frozen sections

While most frozen sections can be predicted from schedules of the operating room and thereby be looked up beforehand, this chapter deals with the most common ones that do not offer such preparation time, thus indicating memorization of how to handle them.

(Gather most common situations.)

Other frozen sections

Although these are generally given on schedules of the operating room, any pathologist may end up suddenly covering for another one, and subsequently be presented with the frozen section case without having had the time to look it up beforehand.

Non-emergent pathology

Also largely a directory of external guidelines and databases.

Non-emergent pathology questions

FINDING GUIDELINES

Which of the following situations does not have comprehensive guidelines available online?

INFECTIOUS DISEASES

Ask what are the main locations to look for infection in a specific autopsy case.

Provide algorithm of gram stain etc. and table of main bacteria by various locations.

Where to find information

INFORMATICS QUESTION

Provide genetic variant in long format.

- Which database is the best to use to look up the pathogenicity of this variant?

 - ClinVar (correct)

 - gnomAD (population frequencies)

 - PolyPhen (likelihood of protein damaging)

 - PharmGKP (associated treatments)

- In ClinVar, what would you enter

 - A1708V (then BRCA1)

Dealing with Internet denialists and their exams

An Internet denialist probably knows about the existence of the Internet, but keeps acting and teaching as if being oblivious of it. An Internet denialist generally takes pride in for example memorizing the chromosome locations of even rare mutations, but when being called in for a frozen section of even relatively common specimens such as brain, lung or skin tissues, they may not know how to differentiate even the most common 90% of diagnoses.

An Internet denialist who has memorized something may assume that pathology trainees should memorize it as well, and entire lectures may largely consist of rants of such items. In reality, when something is encountered and looked up something enough times, it will generally get memorized, and it is generally more efficient to let time tell which situations will be common versus uncommon, rather than trying to memorize knowledge that may never be needed.

An Internet denialist exam is basically any exam wherein the examiner does not have access to the Internet, and typically is not allowed to ask colleagues either, even for non-emergent topics that can conveniently and timely be handled by such resources. Since the Internet and teamwork are fundamental parts of everyday practice, such exams are thereby of a different dimension.

Exam studying

Since exams and everyday practice are generally very different (as per previous section), you should generally study specifically for an exam or study specifically for solving each case you encounter everyday, rather than trying to study any material with the intention of covering both purposes. After all, for a multiple choice exam like the American boards, you don't actually need to know the answer, but just have a feeling of what is the most likely answer among the choices. Also, you will become proficient at what you do: If you read textbooks you will be more proficient at reading textbooks, if you study to solve everyday cases on your table then you will become good at that, whereas the best way of becoming more proficient at multiple choice exams like the American boards is to practice qbanks with a similar multiple choice format. There are multiple ones for the American boards (PathPrimer, PathDojo, BoardVitals, ASCP Resident Q bank), and you should exhaust them and repeat at least the ones you failed the first time, before continuing with other study materials. For highest yield, don't read every explanation for every answer, but just the answers that contradicted your belief, just enough to learn why it wasn't what you initially thought. Also, you don't have to memorize every clue to the right answer, but rather get an idea of what makes the right choice most likely, because that's basically all you need to choose that right answer if it would appear in the actual exam. To check if you got it, you may for example review the correct answers for a test until you almost immediately find them to be reasonable, and repeat the question later if you have the time. If the Qbank shows the average percentage of test takers who got a question right, put somewhat less effort on questions with very low percentage, since you generally have less of an expectation of knowing those.

Fixation

Immersion

File:Adipose tissue with crumpling artifact due to insufficient fixation.jpg

Adipose tissue with crumpling artifact due to insufficient fixation.

Within an hour after removal from the body, tissue samples should generally be placed in vessels with enough fixative to allow them to lie freely in the solution. The standard fixation fluid is generally 10% neutral buffered formalin, which is roughly equivalent to 4% formaldehyde. The ratio of tissue:formalin should be 1:5 to 1:10.

Duration

The duration depends on tissue thickness, where formalin will penetrate and fix the tissue at ~1 mm/hour.

When not to use formalin

The main exceptions to using formalin are mainly:

• Intraoperative consultation.  
• Suspected crystals, such as a tophus or other specimen suspicious for gout versus pseudogout. These should be sent in alcohol or dry, since formalin will dissolve the crystals.
• Suspected lymphoproliferative disorders, such as lymph nodes (or other lymphoid aggregates) with a suspicion of lymphoma, where samples are generally put in a special solution for flow cytometry.
• Need for genetic testing, such as some cases of products of conception.
• Cytology specimens, which are preferably sent fresh (such as in red top tubes) to be processed within a few hours. If processing may be after a few hours, put tubes on ice, or add 50% alcohol.
• Need for microbiology evaluation, mainly bacterial culture. For potentially infectious workups, check with the microbiology lab if they have the tissue they need before putting the specimen in formalin.
• Need for immunofluorescence, such as immune complex-mediated disease, where specific preservation will give better test sensitivity.

If you don't know, and if you cannot soon get in touch with anyone who can guide you, specimens can generally be stored in a fridge in the meantime, even overnight if it is late (but make sure to follow-up as soon as possible in the morning). Until then, don't put the specimen in formalin and don't freeze the specimen.

Gross processing

Following are general notes on selection and trimming in pathology.

Priority

Priority

1. More invasive intraoperative consultations (such as open surgery) 2. Less invasive intraoperative consultations (such as skins) 3. Fresh lymph nodes 4. Fresh breast tissue (should be in formalin within an hour from surgery) 5. Other fresh tissue 6. Tissue in formalin

For prioritizing when you have more than one thing ongoing at the same time, the list at right can be used.

Fresh specimens

The initial processing of fresh specimens is also termed triaging.

• For intraoperative consults including frozen sectioning, see separate article on Emergent pathology.

When triaging a specimen, the measurements are most important as these may change after fixation. Other descriptions can generally be made after the specimen is fixed.

• See also separate article on fixation, including what specimens should not immediately be put in formalin (mostly tophus, lymph nodes and products of conception).

Before cutting

• Confirm that the patient identity on the specimen container matches the identity that will be applied to the gross description and cassettes. {{If the referral or requisition form is available, confirm the patient identity on that one as well.}}

File:Right or left renal stone.jpg

For unclear or potentially ambiguous handwriting (here "Right" or "Left" renal stone), look at the referral or requisition form ((and the medical record if available)).

• (Check for any discrepancy between the specimen description on the container and on the referral or requisition form, such as left versus right.)
• Don't omit any piece in the container, such as ones hidden in wraps.
• Generally measure in 3 dimensions, or in volume, but the greatest dimension is generally enough for specimens less than 0.4 cm.
• Generally weigh entire organs, after having any attached tissue trimmed away if feasible.
• (Note the color of the sample, even when unremarkable, but do not linger on deciding it.)
• Generally, use inking for resection margins where tumor radicality is important. Further information: inking
• (On fatty or greasy surfaces, apply vinegar to emulsify and remove the fat, dry the specimen and then ink. Otherwise, vinegar can be used either before or after inking to "dry" it.)
• (Preferably photograph or make a drawing where slices have been taken.)
• Remove any surgical stitches from samples before microtomy.
• (At least for larger samples, consider looking for medical imaging or biopsy reports in order to better guide the process.)
• Fix bone in formalin prior to decalcification. Use reminders so not to forget bone that is decalcifying.
• Plan in which order to cut different parts so as to be able to take all relevant sections. Generally sample relevant surgical margins and smaller parts first, as these may be harder to find or even be fragmented later on.

Cutting

• When cutting with the longer knives, try to cut in one stroke - do not use like a saw (continuous back and forth)
• Generally, strive to make slices perpendicular to visible interfaces of relevant tissues.
• Generelly dissect and inspect the entire specimen, while keeping relevant parts intact enough for presentation to seniors and/or maintaining orientation.
• Trim tissues for microscopy examination to a thickness of maximum 3-4 mm.

Perpendicular versus en face sections

File:Perpendicular versus en face.jpg

Perpendicular and en face sections

Two major types of sections in gross processing are perpendicular and en face sections:

• Perpendicular sections allow for measurement of the distance between a lesion and the surgical margin.
• En face means that the section is tangential to the region of interest (such as a lesion) of a specimen. It does not in itself specify whether subsequent microtomy of the slice should be performed on the peripheral or proximal surface of the slice (the peripheral surface of an en face section is closer to being the true margin, whereas the proximal surface generally displays more area and therefore generally has greater sensitivity in showing pathology, also compared to perpendicular sections).

• A shaved section is a superficial en face slice that contains the entire surface of the segment.

Tissue selection

When sampling sections to submit for microscopic examination, whenever you sample from something that looks abnormal, generally try to also sample from the same type of tissue that looks normal.

Biopsy wraps, bags and sponges

File:Biopsy wrap, biopsy sponge and biopsy bag.jpg

Items used for submitting specimens: (Biopsy) wrap, (biopsy) sponge, (tissue processing) cassette and (biopsy) bag.

Put the following types of specimens in bags:

• Tiny specimens that need to be poured out from their containers.
• Bloody specimens such as endometrial curettages or products of conception. For products of conception, chorionic villi may otherwise contaminate other specimens. Bloody specimens may stick to wraps, so generally avoid that situation.
• Friable tissue such as urinary bladder biopsies.

Put the following types of specimens in bags, wraps or sponges:

• Other tiny specimens
• ((Any small piece of tissue where there is no leftover specimen to retake sections, since tissues occasionally get lost from cassettes, and the absence of a wrap, sponge or bag in the cassette of such cases points towards a mistake made at gross processing.))

Specimens must be fixed enough to be put on sponges.

H&E staining urgency

(Even in departments where other staff are primarily responsible for determining the urgency of H&E staining of each specimen, still double-check that it is correct if you can, such as by cassette color.) A major indication for rushing cases through H&E staining is a high risk of cancer, especially where immunohistochemistry staining will likely be performed, and the decision and types of staining will be determined by the standard H&E stain. Tissues that are generally rushed are:

• Brain biopsy.
• Lung biopsy.
• Breast needle biopsy.
• Biopsy from known tumor tissue.
• Suspected malignant lymph nodes, including lymphoma. However, these are generally not urgent when submitted together with a tumor, except mainly for the following (which are generally urgent):

• Pelvic sentinel lymph nodes
• Sentinel lymph nodes from known invasive lobular carcinoma (but not invasive ductal carcinoma)

In both these cases, the cases are rushed so that immunohistochemistry can be performed if a metastasis is not readily detected on standard H&E slides, so that it is available by the time the rest of the slides are out. Immunohistochemistry in these cases can detect micrometastases that are not readily visible on H&E stain, but are evident on cytokeratin AE1/AE3. However, if the lab stains such cases regardless of whether H&E stain shows a metastasis or not, then they do not need to be rushed.

Marking cassettes

Use only hard pencil (or specially purchased histology markers), as marks made with pens, Sharpie markers, or scientific freezer-safe markers can get dissolved in tissue processing.

Evaluation of tumors

For evaluation of suspected malignancies such as tumors, the most important aspect is whether it is benign or malignant. If malignant, then staging is necessary. There are generally specific criteria for various forms of tumors, which should be used whenever applicable, but following are some generalizations.

A general approach is to start looking at a slide which seems to contain non-necrotic tumor, and if possible it should also show surrounding non-tumor tissue, so that the interface can be appreciated (and tumors are generally less necrotic at the periphery).

Benign or malignant

	Benign	Malignant
Gross examination	Well demarcated from surrounding tissue	Usually no tumor capsule Possibly: Necrosis Infiltration or invasion into surrounding tissue Bleeding
Microscopy	Almost no irregularities of cellular structures	Nuclear atypia: Enlargement Pleomorphism Nuclear polychromasia, which means variability in nuclear chromatin content. Numerous mitotic figures

• Cellular features of malignant cells versus normal cells.
  Cellular features of malignant cells versus normal cells.
• An increased nucleus-cytoplasm ratio is generally an indication of malignancy.
  An increased nucleus-cytoplasm ratio is generally an indication of malignancy.

Primary tumor versus metastasis

File:Metastasis sites for common cancers.svg

Major metastasis pathways: Main origins and sites of metastases for some common cancer types. Primary cancers are denoted by "...cancer" and their main metastasis sites are denoted by "...metastases".

Indications of a metastasis rather than primary tumor are mainly:

• Tumors that are unlikely to arise at the location at hand.
• Tumors conforming to more likely metastasis pathways.

If a suspected malignancy is present, generally check the patient history for any history of cancer, especially for tumors in more common metastasis sites, which mainly include lung, bone, liver and/or brain. In case of such history, preferably look at the microscopy slides of the past cancer to help determining whether the current case is of the same origin, versus a primary at the current body location, versus a metastasis of yet another location. If there is no known history of cancer, still consider a metastasis of unknown primary origin, especially for suspected malignancies in lymph nodes, liver, lungs, bones, or skin.
Further information: Metastasis

Histopathologic type

For specific diagnoses by organ system, see anatomic diagram on Patholines Main page. This resource will give the main steps towards reaching a diagnosis, but before making a tumor diagnosis, generally be sure that it fulfills the criteria of the condition according to The WHO Classification of tumors, and generally consult an experienced pathologist as well until you feel confident.

Visually, tumors and other suspected malignancies can usually be classified into one of the following groups:

• Gland-like tumors, with tumor cells around clearings
  Gland-like tumors, with tumor cells around clearings
• Squamoid tumors, typically having abundant eosinophilic cytoplasm.[16]
  Squamoid tumors, typically having abundant eosinophilic cytoplasm.
• Spindle-cell tumors, with elongated cells and/or nuclei
  Spindle-cell tumors, with elongated cells and/or nuclei
• Undifferentiated tumors, with few to no visual clues to their origin.
  Undifferentiated tumors, with few to no visual clues to their origin.

Further pinpointing of a specific tumor type is often attained by thinking of one or more possible diagnoses, and looking up their differential diagnoses, followed by comparing their microscopic descriptions and multiple micrographs with the case at hand. When two or more diagnoses seem to fit with the case at hand, consider performing immunohistochemistry. Find relevant target proteins that are expected to stain substantially differently between the possible diagnoses. If it's not evident from initial sources, you may use Immunoquery.com which will generally suggest the most relevant target proteins to distinguish the suspected conditions at hand.

Gland-like tumors

File:Histopathology of adenocarcinoma.png

Typical features of adenocarcinomas. In reality, the appearance varies significantly from case to case. Vacuoles are more prominent in mucinous tumors, but can be seen in serous tumors as well.

Gland-like tumors are mainly evaluated for cellular atypia, architectural dysplasia and invasion, and thereby classified into the following main categories:

• Hyperplastic lesions, lacking significant atypia
• Adenomas, which can range from mild to high-grade dysplastic, yet are generally confined within their anatomic layers, that is, they are not invasive.
• Adenocarcinomas, with the main criterion being invasiveness. Evaluate specifically by location when possible. Some specific locations included in this resource:

• Colorectal adenocarcinoma
• Prostate adenocarcinoma
• Lung adenocarcinoma
• Bladder adenocarcinoma
• Esophageal adenocarcinoma
• Endometrial adenocarcinoma
• Pancreatic ductal adenocarcinoma

File:Well-, moderately and poorly differentiated colorectal adenocarcinoma.png

Degree of differentiation, with example from a colorectal adenocarcinoma.

Generally, adenocarcinomas are categorized by degree of differentiation as follows:

• Well differentiated: > 95% of tumor has glandular formations
• Moderately differentiated: 50 - 95% glandular
• Poorly differentiated: < 50% glandular

If metastatic adenocarcinoma seems to be the case (always consider this in at least lung adenocarcinoma), look at the history and radiology reports for a most likely primary. Generally, perform immunohistochemistry with one or two stains that are most typical for the suspected primary, and optionally add CK7 and CK20 as a broad screening. Further information: Metastasis

Squamoid tumors

These are more or less looking like a squamous-cell carcinoma:

• Main characteristics of squamous-cell carcinoma
  Main characteristics of squamous-cell carcinoma
• Typical well-differentiated nests have cells with abundant eosinophilic cytoplasm. Keratinizing centers are seen as well.
  Typical well-differentiated nests have cells with abundant eosinophilic cytoplasm. Keratinizing centers are seen as well.

Differential diagnoses depend on location, such as:

• Squamous-cell carcinoma of the skin, with multiple differential diagnoses
• Squamous-cell carcinoma of the lung
• Urinary bladder: Urothelial versus squamous-cell carcinoma
• Cervix uteri: Cervical dysplasia

Spindle-cell tumors

For Spindle-cell tumors, the shape of the nuclei is a clue to the diagnosis, with the following tendency:

• Pointed on both ends: True fibroblastic tumors
• Pointed on one end and blunted on the other ("bullet-shaped"): Neural
• Blunted on both ends ("cigar-shaped"): Smooth muscle
• Triangular: Myofibroblastic

Evaluate specifically by location when possible

Further histopathologic subtyping and grading

Beyond determining overall malignancy diagnosis (such as adenocarcinoma), probable origin and staging, classification of tumors into a specific histopathologic type or grade is generally of relatively less value. In cases of clearly non-malignant tumors where it is difficult to determine the specific histopathologic type or grade, it is generally acceptable to conclude the evaluation and report it as such, unless the clinician specifically requests otherwise. For potentially malignant or high-risk tumors, typing and grading often still affects the management, but generally much less so than staging.

Undifferentiated malignancy

File:Histopathology of undifferentiated tumor cells.jpg

Histopathology of a biopsy of a lymph node with cancer of unknown primary origin, showing undifferentiated high-grade tumor cells.

An initial panel of cytokeratin (CK, such as by CK AE1/AE3 cocktail), S100, vimentin and LCA (CD45) can be used (see source article for subsequent work-up).

Alternatively, a more comprehensive panel can be performed upfront, with the most pertinent panel suggested below (with main associated primary origins in parentheses), but it should be tailored to additional clues from each individual case:

File:Histopathology of signet ring cell carcinoma of urinary bladder on mucicarmine stain.jpg

Mucicarmine stain showing signet ring cell carcinoma, with the mucin within tumor cells colored pink/red.

• Mucicarmine or Cytokeratin CAM 5.2 (adenocarcinoma)

• CK7 and CK20 can give a broad indication of the primary site. Still use more specific immunohistochemistry stains instead or in addition where applicable. See image below for main patterns.
• NKX3.1 in males (prostate adenocarcinoma), or PAX-8 or estrogen and progesterone receptor in females (female reproductive tract).
• TTF-1 (thyroid or lung tumor)
• GATA3 (urothelial carcinoma, breast tumor)
• CDX2 (gastrointestinal tumor)
• p63 (squamous cell carcinoma)

• S100 (neural, invasive melanoma)
• LCA (CD45) (hematopoietic)
• Synaptophysin (neuroendocrine)

File:CK7 and CK20 by body location.svg

CK7 and CK20 expression by various body locations.

Non-neoplastic

If a neoplasm has been ruled out for what clinically appeared like a tumor, seek a diagnosis that can be consistent with the clinical findings that caused the suspicion. If no explanation is found on the slides, generally take additional levels on the paraffin block, or more sections from any leftover tissue.

For example, for a breast biopsy of what appeared to look like a mass, and there is no neoplasia, look mainly for dense fibrosis or other fibrous changes, so that you can report it and thereby explain the finding, rather than merely writing "benign breast tissue".

Heterogeneity

After having characterized a suspected malignancy, still screen through it for any significant areas that are different and may need own mentioning, or even change the overall type or grade.

Additional levels or slices

Situations requiring additional material include mainly where tumor is expected but nevertheless not seen on existing slides. Such cases include:

• The gross report or other observation describes a tumor or polyp, but none is seen on microscopy.
• Re-excision does not identify tumor cells in a clearly non-radical primary excision or biopsy.

Also consider more material if the most aggressive pattern is seen in the last available section, in which case more sections are indicated (from the same paraffin block if additional tissue is not available).

Depending on availability and greatest suspicion, additional material is either acquired by taking addition step sections of remaining tissue in a paraffin block, or taking additional slices from the original specimen.

Staging

Staging is generally done by TNM classification. Specific TNM systems should be used whenever applicable, mainly the manual by the American Joint Committee on Cancer (AJCC) if you can access it. Further information: Secrets Otherwise, a general system may be used:

T: size or direct extent of the primary tumor Tx: tumor cannot be assessed Tis: carcinoma in situ T0: no evidence of tumor T1, T2, T3, T4: size and/or extension of the primary tumor N: degree of spread to regional lymph nodes Nx: lymph nodes cannot be assessed N0: no regional lymph node metastasis N1: regional lymph node metastasis present; at some sites, tumor spread to closest or small number of regional lymph nodes N2: tumor spread to an extent between N1 and N3 (N2 is not used at all sites) N3: tumor spread to more distant or numerous regional lymph nodes (N3 is not used at all sites) M: presence of distant metastasis Further information: Metastasis M0: no distant metastasis M1: metastasis to distant organs (beyond regional lymph nodes)

File:Histopathology of a lymph node with metastatic invasive ductal carcinoma from the breast.jpg

For positive lymph nodes, generally also note any extranodal extension, and the size thereof.

Put your main focus on features that will determine the final stage. For example, if you see a lymph node involved by cancer, the presence or absence of lymphatic invasion is no longer critical, but rather the presence or absence of additional involved nodes or distant metastasis. If a stage-defining finding is uncertain, generally fall back to the lower stage.

For the size, the greatest dimension of the tumor is most important. Second and third dimensions (preferably at right angles compared to each other) are optional. Use the largest measure for each dimension. For example if one slide shows a tumor measuring 2.0 x 1.0 cm, and another slide shows the same tumor measuring 1.5 x 1.5 cm, then the tumor can be reported as measuring 2.0 x 1.5 cm. The third dimension can be estimated from gross measurement, or, if the tumor is entirely submitted, adding together the presumed thickness of each slice where tumor is found microscopically. For excisions with less than a centimeter of tumor, and where there has been a previous biopsy, consider looking at the size of tumor on the previous biopsy, which may be the largest measurement, and therefore the measurement of choice for staging.

Nx: lymph nodes cannot be assessed also applies when you only find lymph nodes that are not within the physiologic drainage path of the cancer, and they are benign.

Radicality

File:Histopathology of radically excised basal-cell carcinoma with separation artifact.jpg

If tumor is seen at edge of the sample, but it is not inked, consider confirming the finding with adjacent microtomy levels, especially if no ink is seen on an inked surgical margin. In this case, a separation artifact in top image has removed a surgical margin of connective tissue, seen on adjacent microtomy section in bottom image.

Determine if malignant cells are located close to, or even in, any surgical resection margins.

Lymphovascular invasion

Lymphovascular invasion should always be mentioned. When present at margins, it does not count as tumor extension.

• Endometrial cancer with lymphovascular invasion.
  Endometrial cancer with lymphovascular invasion.
• 
  If unsure whether a case is true lymphovascular invasion or a retraction artifact (imaged), use immunohistochemistry for D2-40 to highlight lymphatic vessels or CD-31 for blood vessels.

Molecular workup

Ensure that any cancer undergoes reflex testing where applicable by local guidelines. When they are not applicable, a rule of thumb is to order individual genetic testing if there is a need to test up to 2 genetic targets, and to order genomic sequencing if more targets need genetic testing (not counting immunohistochemitry or other more easily performed tests).

When needing to send out tissue to an outside laboratory, follow their requirements and guidelines for each test. Generally, choose the tissue block with the greatest amount/area of the highest grade malignancy. For molecular proliferation tests (other than immunohistochemistry) such as Ki67, avoid samples with previous biopsy site or inflammation (as these will cause a false high proliferation rates). On the other hand, for next-generation sequencing, hemorrhage, necrosis and adipose tissue does not need to be minimized, as these contain only little genetic material.

Reporting

File:Histopathology of pancreatic adenocarcinoma with treatment effect.jpg

Also note "treatment effect", seen as fibroelastotic tissue, here with scattered remaining tumor cells.

For cancers, generally include a synoptic report, such as per College of American Pathologists (CAP) protocols at cap.org/protocols-and-guidelines. If there is no CAP synoptic available for the cancer type at hand, attempt to find one in the latest AJCC Cancer Staging Manual (see the Secrets article), but make sure to use pathologic staging (with a p preceding the T, N or M) rather than clinical staging.

If a surgery produces a specimen with cancer, as well as re-excisions from certain directions, you should preferably give the closest distance to margins in each specimen, as well as the closest distance overall in a synoptic, for example:

A. (Specimen with most of the cancer) (...) Invasive carcinoma is present at inked medial margin (see specimen B for final medial margin), and is located 0.3 cm from the lateral margin. B. (Re-excision in the direction of the medial margin) (...) Invasive carcinoma is located 0.5 cm from the new medial margin. Synoptic report (...) Distance from invasive carcinoma to closest margin: 0.3 cm Closest margin(s) to invasive carcinoma: Lateral

If possible, generally include features of any previous biopsies or smaller excisions in synoptic reports and staging. For example, if staging is based on tumor size, and the tumor size in a previous excisional biopsy corresponds to a higher stage than the size of residual tumor in a subsequent wider excision, then the report of the latter should give the higher stage, with a comment thereof, such as:

pT__

- Based on previous excisional biopsy (specimen ID: ______)

  See also: General notes on reporting

Reporting

Following are general notes on reporting in pathology.

• Save your digital work frequently, and also before you leave a computer, even if you think you'll be back shortly. If you have many small specimens to write up in the same report, you may want to save every 2 to 3 specimens. It doesn't matter how much time and effort you spend on something if you're just going to let it disappear in the next glitch.
• Double-check your report, especially if you copy-pasted and adapted a previous report rather than using a template with blank fields or making your report from scratch.

Components

Selection and trimming

From the stage of selection and trimming, a histopathology report should preferably include:

• Case:

• Patient identification and/or sample number
• Type of tissue sample as described on container

• Gross processing:

• Dimensions of original tissue
• Directions or other features of any inked surfaces.
• Generally the weight of larger samples
• Dimensions of pathologic components
• Whether the entire specimen or representative sections were submitted.

Microscopic evaluation

• Specimen chronology, often A, B, C, etc., at least where there are multiple specimens from the same case. With multiple specimens, preferably write out the chronology for all of them first, so that you don't miss reporting any of them later.
• Specimen type and/or surgery type, such as "appendix, appendectomy", for clarification. This is not necessary at all departments. For the procedure, use the same term as the operating report whenever possible.
• Microscopic description. This is not always necessary, but should be included if the diagnosis is uncertain. One systematic approach is to describe findings from largest to smallest ones. For example, a description of a tumor can start with the demarcation of the tumor, followed by texture, cell shapes, nucleus shapes and chromatin appearance.
• Diagnosis or most probable diagnoses.

• If the diagnosis does not clearly account for all conditions that were requested, suspected or asked to be ruled out by the referring clinician (such as stated on the requisition form), you need to classify the specimen as "positive for" versus "negative for" for each such condition, or give a reason for why an evaluation thereof could not be made.

• In case of malignancy or suspected malignancy:

• Depth or most distant invasion of malignant findings. Depending on location, it may need to exclude important pathways, such as vascular, neural and/or through capsules or other layers.
• Whether the resection is radical or not.

Depth

Factors supporting a relatively more comprehensive report, particularly in the inclusion of negated findings:

• Lack of explanation from existing evidence. For example, an inflamed appendix that fits the medical history does not need detailed mention of harmless incidental findings.
• Prospective review: If your report is likely to undergo double-reading by another pathologist before sign-out, it should either be more detailed, because the doctor who will do the double-reading then gets an idea of your thought process, including what you have looked for versus what may still need to be evaluated. If you know who will do the prospective review for a report of yours, you may alternatively convey your thought process by other means such as directly talking to that person.
• Highly suspected locations, such as given from the referral.
• Difficulty in obtaining the specimen, such as a CT-guided biopsy versus a skin shave.
• Defensive precautions, which appears to be more common among doctors in the Unites States compared to for example Europe.

Multiple instances of the same type of pathology (such as lung nodules) can often simply be reported as such, at least with a particular mention of the largest or the most severe example thereof.

Uncertainty

Words, from
most likely to
least likely

(is) positive for

probably likely

suggesting

suspicious for

possibly

(benign condition) cannot be excluded

not likely

(malignant condition) cannot be excluded

negative for effectively ruling out

When something looks very much like a specific entity but you are not sure, preferably use "-like" (or when feasible, "-oid" such as squamoid for squamous-like cells).

When the clinical picture strongly favors a certain condition, and the pathology favors it as well, findings are generally described as "consistent with". Sometimes, "bordering on" can be described when the picture almost fits specified criteria of a specific diagnosis.

It is alright to consider the diagnosis of a pathology report to be a combination of the clinical picture and what can be seen on the specimen. For example, if the microscopy picture is uncertain, you may to a certain degree tend towards the diagnosis that best fits the clinical picture. However, mention differential diagnoses if they are still significantly possible, and would confer a different treatment or another substantially different consequence.

For both findings and diagnoses, is preferable to write "negative for..." rather than "no..." to emphasize the possibility of false negative findings.

Synoptic reports

For cancers, generally include a synoptic report, such as per College of American Pathologists (CAP) protocols at cap.org/protocols-and-guidelines. However, synoptic reports are generally not needed for tumor metastases.

Sizes

Whenever possible, give numerical quantities of sizes, rather than descriptions that are subjective (such as "small" or "large") or variable (such as "apple-sized").

Tailoring

The information contained in the reporting sections in this resource assume that the clinician has requested the exam for the topic at hand, but should still be tailored to any particular questions or requests by the clinician. Any relevant findings beyond the issues or questions raised by the clinician should also be mentioned.

As there are generally local practices about how to write reports, it is recommended to have either a personal or practice-specific repository of report templates that you can copy-paste for various cases. When doing so, however, use marks or empty spaces for relevant findings that are frequently changed in the template. Such marks should be conspicuous, so that the report clearly looks unfinished if you haven't tailored it to the case at hand (such as "...measuring _____."). Thereby, you avoid omissions or even wrongly entered information from templates.

The most important findings are preferably moved to near the top of the report if feasible.

Example of report format:

A. Organ, side/site, procedure: Diagnosis 1. Diagnosis 2.

Wording

If a certain grammatical rule has a risk of making the report less clear to the reader, ignore that rule in that situation.

Restrict acronyms/abbreviations to those who are certainly well known among all doctors, such as "cm".

Generally describe what can be seen rather than processes (such as preferring "an abundance of" rather than "proliferation of").

If using a dictation device, avoid "no", and instead use "negative for" (and "positive for" in opposite cases), since there's a risk of "no" not being transcribed and thereby creating the opposite meaning.

Avoid "evidence of" unless you feel comfortable with the legal implications of its meaning in the report.

Whenever there is text needing formatting (text size, font type and/or UPPER vs lower case), it is generally most efficient to do it all at once after all the text is written.

Skin excisions

In skin cancers, use "peripheral" or "radial" margins (whereas "lateral" margin should be reserved for the margin opposite to the medial margin).