Learning pathology

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Author: Mikael Häggström [note 1]
The goal of this resource is to make a new pathology trainee able to properly handle at least 70% of cases that are expected at an average general pathology department, including the exclusion of the most pertinent differential diagnoses thereof. Its aim is to present you at least one way of doing things that is at least adequate for a particular situation, so that although there may be various routines at various locations, adherence to these methods should not result in a worse reprimand from a senior than "although that was adequate, that is not how we do it here". Still ask for help whenever needed, such as first time you are doing something, or whenever you are not sure about what to do, especially when doing something potentially irreversible.

What a pathologist needs to memorize

The best method for memorization is generally through repeated exposure in everyday practice, and the scope thereof will depend on your eventual location and subspecialty, and you will eventually forget everything else, more or less. Yet, the following things are most important for a pathologist trainee 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: The most common and dangerous situations where a pathologist may not recognize the need to look something up further or ask a senior colleague, or where a significant risk of diagnosis error remains after doing so.
  • Interpretation of non-written results, including patterns and signs which can be seen grossly or under the microscope. It confers the ability to translate visuals and other more or less non-verbalizable information into words that can be looked up if needed, and conceive the most likely diagnoses based on both describable and more abstract appearances.
  • Proficiency in diagnosing equivocal or borderline cases where readily available sources and evidence usually deal with discrete and specific disease entities and subcategories thereof. 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. After all, you will get by with effectively handling the regular cases wherever you work, so that you will have time to study or ask others for unfamiliar cases, as long as you know your pitfalls, and have an idea about your unknowns:
  • Having an idea of one’s unknowns; being aware of a lack of knowledge in unfamiliar fields. For example, a pathologist generally does not need in depth knowledge about diseases that are generally sent out to specialized centers (such as pediatric musculoskeletal oncology), but just enough to be able to suspect such diseases. In the same manner, a pathologist needs to have an idea of the optimal limits of practice, between what should optimally be handled personally by the pathologist and what is better handled by others, including senior colleagues, technicians, pathology assistants, junior colleagues and artificial intelligence.
  • Where to find information for various situations. It includes which person or which search engine is most useful for various clinical situations. See the Using resources section below for further information. Similarly, a pathologist often needs to be efficient at finding what is relevant among a large amount of information, and be able to integrate it into a decision or a relatively short report. For questions where a look-up does not readily give the answer, a new trainee usually gets satisfactory replies even from senior trainees, but the more experienced you get, the more you need to establish contacts with particular people, such as certain subspecialties, who are most likely to be able to answer your questions when needed.
This resource aims to cover what you need to memorize as a first year pathology trainee.
  • How to distinguish memorization-worthy versus look-up versus practically useless information. With the ease of access to pathology information on the Internet through smartphones and computers, those studying for the everyday practice as a pathologist should not waste time memorizing what can essentially always be conveniently and timely looked up when needed. This includes most of the content of books and web pages that are sorted by names of diseases and conditions, because if the name of a disease is already known, then it can relatively quickly be looked up when needed in such sources. When finding relevant look-up information on the Internet or local repositories, it is generally enough to remember enough of its related words in order to find it again. After all, other doctors and even laypersons can look up diseases and conditions themselves, without the need for a pathologist consultation, so the expertise of memorizing such readily available information is expendable. Similarly, electronic systems are better suited than the human brain for the storage and rapid retrieval of databases of for example immunohistochemistry and genetics results of various diseases. The topics listed in this section are already immense enough to cover a lifetime of learning. Learning pathology therefore optimally involves the memorization of where and how to find look-up information, rather than directly memorizing such information. Therefore, if you need to choose a textbook to study, then choose one that you will always be able to quickly reach through your smartphone whenever you need its look-up information. Accordingly, the final aim of this resource is to help pathology trainees to give accurate and clinically useful reports to clinicians, in synergy with the resources that are available in everyday pathology practice, and to establish routines to continue such practices. The intended end result is to help clinicians to improve the lives as much as possible to as many people as possible, even if it means forgoing the prestige of becoming a walking encyclopedia. It also means finding high-yield learning sources, for even if they may take longer time to find, you will be better prepared for real life than when you study low-yield knowledge, which includes statistics that is very unlikely to be used diagnostically, mainly because their calculations would be so complex that it is not worth it. For example, in reality you generally have a pattern of signs and other findings and you want to know the likelihood of each differential diagnosis, and for this purpose you only get limited help by knowing the reverse likelihood of what percentage each individual condition is to display the finding, because it would still be necessary to also know for example the epidemiology of each disease to calculate its likelihood. Instead, the optimal studying is generally not of diseases individually, but rather of patterns of signs and other findings and the likelihoods of each differential diagnosis thereof. Arguably the best method of acquiring such knowledge is to be involved in many real cases at a pathology department, making your own diagnostic thinking of them, and correcting your thinking based on how you differed from a senior's report. The next best method is arguably to solve virtual cases such as found in pathology qbanks.
  • How to efficiently study for exams that contain questions that require direct memorization of look-up (or even practically useless) information, as long as such exams are in the way of practicing pathology. The best approach is arguably to spend enough time and effort on memorizing what is memorization-worthy, to the point where you will pass an exam even if you will fail multiple questions that require memorization of look-up or practically useless information. However, when starting pathology training, do not focus on studying for any final exams that are years away, because the content on such exams is systematically very different from what you need to know initially. For instance, you initially need to know how to handle the common types of cases, but exam makers on the other hand, in their effort to distinguish those who have studied more extensively than others, will systematically choose presentations that are not commonly encountered. Further information: Secrets
Type of information Examples (usually) Learning approach
  • Emergent matters
  • Pitfalls
  • Interpretation of non-written results
Directly memorizing it.
  • Textbooks and websites organized by names of diseases and conditions
  • Immunohistochemistry results
  • Associations between genetic mutations and diseases, and related molecular biology.
  • Classifications such as cancer staging
  • Large tables and diagrams
  • Long lists
Knowing where to find it when needed, and how to use it.
  • Diseases individually
Instead studying patterns of findings and signs, and how they support various differential diagnoses.
Practically useless
  • History
  • Most of scholarly articles
  • Most clinical management
Avoiding, or skipping to potentially useful parts.

Whether any piece of information is useful versus useless depend mainly on:

  • The likelihood of a situation where the information is useful.
  • The benefit versus detriment of having versus not having the information at hand in such a situation.

The clinical management aspects that can be useful for pathologists to learn are the thresholds for pathologic findings that substantially change the clinical management, such as a cancer stage that determines whether clinicians will try to completely remove all tumors versus treat palliatively. With such knowledge, pathologists can put relatively more effort on the cases and parts thereof that make the most difference to the patient. Otherwise, clinical management knowledge is generally useless to a pathologist.

Lectures may be memorization-worthy depending on the content, but a lecture of look-up-information is practically useless unless you maintain a system to quickly retrieve the information when needed. Thus, sometimes, it is better to study something more memorization-worthy while pretending to listen to a lecturer.

Also keep in mind that pathology in our look-up era is mainly a processing work rather than a memorization one, since your most important skills are to interpret findings, and sometimes involve a vast amount of information in order to suggest the most likely diagnoses. Again, arguably the best method fur such purposes is solving real or virtual cases.

Using resources

This resource is written with the intention to teach you what to do in the most common situations you are expected to encounter during your first years of pathology training, at least until the point that you are usually fairly confident about what disease or condition you have at hand, because then you know what words to use to look it up in the vast literature out there. At that point, the fastest way to get more information is generally by Googling the disease or condition name, followed by pathology outlines (which is generally the most likely to quickly give you the information you need), since Internet will always be readily available in pathology.[note 2] The most efficient method of studying to solve a case at hand is to not read articles in their entirety, but to scroll directly to the parts that are most likely to give you the information you need (generally past the first half of Pathology Outlines articles).

Specific search methods for some specific purposes include the following (and the author has no financial or other conflicts of interests in mentioning any of these):

  • Google, and then clicking the Images tab, if you just want to see more micrographs of the disease or condition. Even when you don't have a clue what condition you are looking at, you may find something that looks similar to your case by entering words you would use for the microscopic findings that you see.
  • Adding cancer.net staging in Google searches for definitions of cancer stages, for example Googling prostate cancer cancer.net staging. The first search will then generally be the one from the American Society of Clinical Oncology.
  • Considering a subscription for ImmunoQuery[notes 1] (or equivalent database if you find one) in order to generate the most pertinent immunohistochemistry stains when you have two or more differential diagnoses for a case at hand. It is not sufficient to just memorize a few usually positive or negative immunostains for each disease and condition, because what you need in reality is to figure out what immunostains to order so that you can pinpoint one diagnosis among your multiple differentials. To master that, you will need to memorize a vast amount of immunostains and at what percentages they are positive for a vast amount of diseases and conditions, or you can have an online service like ImmunoQuery do that work for you. After all, in pathology there is essentially no immunohistochemistry that is so emergent that you do not have the time to use a computer or smartphone to look it up.
  • ClinVar to look up the pathogenicity of specific genetic variants/mutations.

If the above resources do not provide a sufficient answer:

  • Googling what you are looking for. You may add the word pathology or equivalent if results are too clinical or layman-oriented. Before even reading the title of results, first look at the URL. If it is from a reputable organization then you may proceed to check if the title is pertinent to what you are looking for, but if it is from an unfamiliar site then you should only proceed if you don't find a better source among your search results, and you will need to look for additional proof of reliability such as authorship of the content in order to use it in the diagnostics of any case. You can generally rely on more articles for presumably well-established topics (such as anatomy, and relatively common diseases) than for potentially controversial and experimental topics, in which case you generally need to ask yourself if the author has a conflict of interest.

Ask a colleague at least whenever your own memory or a resource search is not enough, and there is a significant risk that you may do something irreversible that will negatively affect a patient.

Regarding lectures and knowledge your colleagues will tell you, make a judgment for each piece of information if it fits a criterion for memorization, or if it merits being written down somewhere you can find it so that you can look it up when needed.

Wikipedia often shows up among top Google results, and is generally accurate.[1]

Whenever possible, use textbooks and other sources that you can quickly access online, because you will likely always be close to the Internet, but not always close to your collections of physical material. Keep in mind that for the vast majority of content, you only need to have a hunch of where to find it again when needed, or what search terms to use. If something may be difficult to find again, you may add it to a personal digital collection to be readily available in times you need it.

Strive for sources that, taken together, are comprehensive enough for the presentation at hand. For example, if you first look in a resource on only benign conditions that may cause your presentation, you generally need to look for another source that includes malignant conditions as well.

Generally skip any part that tries to explain a microscopic appearance using only words, since a Google image search is generally more useful.

Test question

A 4 year old girl with a renal mass
Histopathology of Wilms' tumor, original.jpg
Histopathology of Wilms' tumor, annotated.jpg

You are a new resident at a community hospital that is closely affiliated with a university hospital. The attending gives you a couple of slides from a case that is not yet signed out to preview and then come back with what you think would be the next steps. You are also told to share them with a med student who rotates at the department. One of the cases is from a kidney of a 4 year old girl. You look up the patient's history and she was admitted for orthopedic care for multiple fractures, and CT incidentally found a kidney tumor where workup was initiated as an inpatient. Microscopy shows the image at right. The med student has a smartphone and by googling "common kidney tumors in children", Wilms' tumor (also known as nephroblastoma) shows up as one of the top choices. You look up the condition on Pathology Outlines and the case seems to fit the microscopic description with its 3 typical components (second image at right).[2] On the same web page you also quickly see the following pieces of look-up information:

  • Risk classification systems, where for example "COG intermediate risk" requires favorable histology and no evidence of anaplasia.
  • That there are no specific/diagnostic laboratory findings.
  • A bunch of associated genetic changes (WT1 (11p13), CTNNB1 (3p22), IGF2 (11p15), TP53 (17p13), MYCN (2p24), and 1q gain).
  • A bunch of associated immunohistochemistry results in the tumor, related non-neoplastic tissue, as well as in notable differential diagnoses (WT1, PAX8, vimentin, CD56, CD57, cytokeratins, EMA, desmin, cyclin D1, BCL2, CD34, myogenin, MyoD1, INI1, Glypican 3, AMACR, CK7, melanocytic markers (MelanA, HMB45), BRAF V600E, TFE3, TFEB, BCOR, and FLI1)

Which of the following would be the best next step if you were to decide yourself?

  1. Diagnosing Wilms' tumor, COG intermediate risk, based on the shown microscopic view alone.
  2. Look at the complete blood count for diagnostic findings.
  3. Order genetic testing for WT1 (11p13), CTNNB1 (3p22), IGF2 (11p15), TP53 (17p13), MYCN (2p24), and 1q gain.
  4. Order immunohistochemistry for WT1, PAX8, vimentin, CD56, CD57, cytokeratins, EMA, desmin, cyclin D1, BCL2, CD34, myogenin, MyoD1, INI1, Glypican 3, AMACR, CK7, MelanA, HMB45, BRAF V600E, TFE3, TFEB, BCOR, and FLI1.
  5. Say "I don't know" and ask for help.
Correct answer
Say I don't know and ask for help.png

A major skill of a pathologist is having an idea of one’s unknowns. Furthermore, pediatric oncology is generally outside the limits of independent practice of any individual pathologist, generally requiring at least consultation with a colleague before diagnosis, classification and decisions about further workup (which in this case may be made at a pediatric oncology center). Thus, even if you though you knew how to proceed on your own, saying "I don't know" and asking for help is still the most correct as a new resident for a case like this.
Incorrect answers

You can skip reading these if you are already agree with the explanation above.

  1. Although the microscopic view that is shown is enough to diagnose Wilms' tumor, it is not enough to classify it as COG intermediate risk without first having looked at the entirety of the microscopy slides to exclude evidence of anaplasia.
  2. There are no specific/diagnostic laboratory findings of Wilms' tumor.
  3. A senior or specialist consultation would be needed in order to find out which genetic tests would actually be worth performing in this case, even after reviewing the history or asking a clinician for any suspected syndrome associated with Wilms' tumor.
  4. The choice of immunohistochemistry panels should be based on which ones most efficiently distinguish the possible differential diagnoses of the case at hand, and not just which ones are associated with the lead diagnosis. As with genetic testing, a senior or specialist consultation would be needed in order to find out which immunohistochemistry tests would actually be worth performing in this case. Further information: Immunohistochemistry

Using this resource

In this resource, it is recommended to read attentively until the end of the emergent pathology section. That part can be regarded as mainly describing concepts, which are relevant to read through and understand or at least consider. The rest will mainly provide guidelines for various situations, such as when you are presented with a biopsy of the gastrointestinal tract. Memorization-worthy information will generally be highlighted by: Memorization-worthy: , otherwise it is recommended to scroll quickly through such situation-based chapters, just to get an idea of what kind of information is available there, and then keeping this resource at a known location for whenever you are in that situation.

  • Memorization-worthy:  This resource is available open-access and ad-free by googling patholines and then Starting pathology (handbook).

This resource is aimed at presenting the most important knowledge that you will need when starting pathology. For further knowledge that you will need as a pathologist and any subspecialization, the best way is to learn from reality, by solving the cases and problems that get presented to you, and thereby look specifically for the information that you will need among the immense literature and other information that is out there.

Also, this resource assumes that you use additional sources when needed (such as The WHO Classification of Tumors or others in the Using resources above). Therefore, it will not simply repeat such information, but may display external links to further information.

This resource also assumes that you will ask a colleague for advise if you see an unfamiliar presentation, and any literature lookup thereof still does not explain it. Therefore, this resource will focus on the most common presentations and the main differential diagnoses thereof, which may include rare conditions if for example the clinical management thereof would be significantly different. On the other hand, most rare conditions that generally have distinct presentations will be omitted. Therefore, keep in mind that there are many such rare conditions that you do not know about, so keep asking colleagues whenever a presentation remains strange to you.

Be tolerant to encountering many repetitions of the same content in related articles, since for example a cervical biopsy and a cervical cone have similar microscopic evaluation.

Using question banks

To test your knowledge on memorization-worthy information, seek questions that present you with a possible real life situation, as well as all pertinent information you can readily look up before needing to answer the question, so to ensure that it tests you on pertinent information as per the items earlier in this chapter. On the other hand, don't waste time on questions whose answer requires memorization of look-up or practically useless information (except if you want to practice looking up the answers online). There are about 5000 questions in PathPrimer, PathDojo and BoardVitals combined, so you can be picky about what questions to focus on.

Consider the usefulness of each question before spending significant time memorizing its answers or explanations, in order to maximize the useful knowledge you will learn overall. Generally, skip questions that test you on look-up information and practically useless information. Whenever you have a question where you can not picture in what real life situation it would be relevant to remember, then you can generally assume that it never will be. For questions that consists of a useful item together with a more useless one, only learn the the useful part and move on. If you can, flag/mark questions on memorization-worthy information that you did not know, and move on fairly quick on those as well, and later revisit those questions specifically if you have the time, as repetition is generally more efficient than lingering.

A common sign that a question will deal with look-up or practically useless information is where it asks which of the alternatives is false or correct for one particular condition, and the alternatives are relatively heterogenous (such as one dealing with diagnosis and another one dealing with prognosis). The high prevalence of such questions is mainly because they are easy and quick create, because the question creator can simply look up a condition, choose some more or less random facts, and then change small details to create alternatives. It requires no real life experience in everyday pathology practice, and learning from such a question is hence generally not useful for that purpose either. The thought processes of real life pathology is generally the opposite of this, because you are generally presented with a specific location, gross appearance and microscopic appearance, and you need to practice on finding the most likely causative condition thereof among many differential diagnoses. Even other kinds of memorization-worthy pieces of information generally have a more limited scope among alternatives (like knowing the optimal staining duration in hematoxylin for a frozen section among alternative durations (see Emergent pathology). Thus, to practice your knowledge in memorization-worthy pathology, it is generally most efficient to skip false-versus-correct questions, in order to spend your limited time on something more worthwhile. Similarly, questions are in general rather low-yield whenever they deviate from the realistic direction.

Other signs of unrealistic and therefore rather low-yield questions include those that mention what kind of test identified the condition, but does not give you the test result (such as a case presentation that includes "Serology identified the organism").

If you have gone through all 5000 questions of the main question banks, and still have plenty of time for a second round, then you may work on lower yield questions as well. For example, you may practice on looking up answers for look-up questions, unless the presentation makes it clear that you cannot timely and conveniently do so (such as being in a rush during a frozen section).

Test question

A question on a question

You want to practice your memorization-worthy knowledge in real life pathology and not for exams (Further information: Secrets ). You find the following multiple choice question: "Which of the following statements for squamous cell carcinoma (SCC) of the skin is false?"

  • For staging of SCC of the of the head and neck, pT1 corresponds to a diameter ≥ 2 cm and < 4 cm (this is the false alternative, as this defines pT2, whereas pT1 is defined as ≤ 2 cm)[3]
  • Most patients have a favorable outcome after surgical resection.
  • It occurs most often in sun exposed areas.
  • It often presents as a hyperkeratotic scaly plaque.
  • Microscopy typically shows carcinoma of keratinocytes that infiltrates the dermis.

What is the most efficient way of dealing with this question for real-life pathology practice?

  1. Choosing an answer, then thoroughly reviewing each alternative, as well as the question explanation.
  2. Like the first alternative, but only if you answered the question wrong.
  3. Only carefully review the single association you need to answer the question correctly (in this case, that for SCC of the skin, pT1 is defined as ≤ 2 cm).
  4. Skip this question and move on.
Correct answer

Skip this question and move on.png
The answer alternatives of this question are all over the place (a mix of prognosis, location, staging, gross description and microscopic description), which usually means that it was created by just looking up the condition in a resource and picking information from there, resulting in a collection of what is usually just look-up information.

Incorrect answers

You can skip reading these if you are already agree with the explanation above.

1 and 2. These are waste of time.
3. If this was a question of memorization-worthy information, or if you were studying for an exam, this would generally be the correct answer. However, staging of cancers can essentially always conveniently and timely be looked up when needed, so this is not memorization-worthy for everyday pathology practice.

General notes edit

Further reading:


  1. The author has no financial or other conflict of interest in the mentioning of ImmunoQuery.
  1. For a full list of contributors, see article history. Creators of images are attributed at the image description pages, seen by clicking on the images. See Patholines:Authorship for details.
  2. If you worry about Internet outages, then it is still much more worthwhile to purchase satellite Internet as a backup (which costs $50 to $100 per month) than to try to memorize the Internet.

Main page


  1. Kräenbring, Jona; Monzon Penza, Tika; Gutmann, Joanna; Muehlich, Susanne; Zolk, Oliver; Wojnowski, Leszek; Maas, Renke; Engelhardt, Stefan; et al. (September 24, 2014). "Accuracy and Completeness of Drug Information in Wikipedia: A Comparison with Standard Textbooks of Pharmacology ". PLOS ONE 9 (9): e106930. doi:10.1371/journal.pone.0106930. PMID 25250889. Bibcode2014PLoSO...9j6930K. 
  2. Ellen D’Hooghe, M.D., Gordan M. Vujanic, M.D., Ph.D.. Kidney tumor - Childhood tumors - Nephroblastoma. Pathology Outlines. Topic Completed: 16 September 2020. Minor changes: 6 October 2021
  3. Shaofeng Yan, M.D., Ph.D.. Skin nonmelanocytic tumor, Carcinoma (nonadnexal), Squamous cell carcinoma. Pathology Outlines. Topic Completed: 13 January 2020. Minor changes: 8 December 2021

Image sources