Invasive lobular carcinoma

Author: Mikael Häggström
Invasive lobular carcinoma (ILC):

Contents

Gross examination

As per:

• Breast biopsy or excision

or mastectomy.

Microscopic evaluation

Invasive lobular carcinoma.

ILC may be subtle on low magnification (left). Higher magnification (right) shows invasive growth pattern and vesicular nuclei with prominent nucleoli.

Characteristics

The "classic" pattern is round or ovoid cells with little cytoplasm in a single-file infiltrating pattern, sometimes concentrically giving a targetoid pattern.

Subtyping

The histologic patterns mainly include:

Type	Prevalence	Description	Image
Classical	40%	Round or ovoid cells with little cytoplasm in a single-file infiltrating pattern, sometimes concentrically giving a targetoid pattern
Mixed	40%	No dominant pattern
Solid	10%	Sheets of classical-appearing cells with little intervening stroma.
Alveolar	5%	Aggregates of classical-appearing cells
Tubulolobular	5%	Cells form microtubules in >90% of tumor (smaller than in tubular carcinoma)
Pleomorphic		Classical-appearing but with pleomorphic cells. It may include signet-ring cells, or plasmacytoid cells (pictured) which have abundant cytoplasm and eccentric nuclei.

Differential diagnosis

Lobular carcinoma in situ.

• In invasive lobular carcinoma, malignant cells have penetrated the basement membrane, in contrast to lobular carcinoma in situ.
• Invasive ductal carcinoma typically has duct-forming tumor cells rather than single files of tumor cells. In uncertain cases, stain for E-cadherin and p120:

• 

  Invasive ductal carcinoma, with occasional entrapped normal ducts (arrow).

• 

  E-cadherin is negative in invasive lobular carcinoma (shown), but has membranous staining in invasive ductal carcinoma

• 

  p120 has cytoplasmic staining in invasive lobular carcinoma (shown), but has membranous staining in invasive ductal carcinoma

Staging

Stage by the TNM system as follows in sections below.

Also, look for any angiolymphatic invasion. If present, check whether it reaches outside the tumor, and if so, how far. Give greatest dimension (,or 3 dimensions, generally by adding up the estimated thicknesses of involved slices)).

Primary Tumor (T) Tumor – Depends on the tumor at the primary site of origin, as follows: TX: inability to assess that site Tis: ductal carcinoma in situ (DCIS), lobular carcinoma in situ (LCIS) or Paget's disease of the breast Measurements can be made by marking the tumor on microscopy, and then measuring between the markings, which may overlap between multiple slides as shown. T1: Less than 2 cm T1a: 0.1 to 0.5 cm T1b: 0.5 to 1.0 cm T1c: 1.0 to 2.0 cm T2: 2 to 5 cm T3: Larger than 5 cm T4 T4a: Chest wall involvement T4b: Skin involvement T4c: Both 4a and 4b T4d: Inflammatory breast cancer, a clinical circumstance where typical skin changes involve at least a third of the breast. Regional Lymph Nodes (N) Lymph Node: When sentinel lymph nodes are submitted together with a biopsy or excision of a suspected or previously confirmed invasive lobular carcinoma, and you don't see any involvement on the H&E stain, order immunostain for CK AE1/AE3 in order to visualize otherwise occult lymph node involvement. However, this is not mandatory for invasive carcinoma with lobular features, or non-sentinel lymph nodes. The lymph node values depend on the number, size and location of breast cancer cell deposits in various regional lymph nodes, such as the armpit (axillary lymph nodes), the collar area (supraclavicular lymph nodes), and inside the chest (internal mammary lymph nodes.) Each stage is as follows: N0: There is some nuance to the official definitions for N0 disease, which includes: N0(i+) : Isolated Tumor Cell clusters (ITC), which are small clusters of cells not greater than 0.2 mm, or single tumor cells, or a cluster of fewer than 200 cells in a single histologic cross-section, whether detected by routine histology or immunohistochemistry; N0(mol-): regional lymph nodes have no metastases histologically, but have positive molecular findings (RT-PCR). N1: Mobile ipsilateral axillary nodes. Lymph node clusters 0.2 - 2.0 mm can be called "micrometastasis". At least one carcinoma focus over 2.0 mm is called "Lymph node metastasis". If one node qualifies as metastasis, count all other nodes even with smaller foci as metastases as well. Critical numbers of involved nodes: 1-3, 4-9, and 10 and over. Note any extranodal extension. N2: Fixed/matted ipsilateral axillary nodes. N3 N3a – Ipsilateral infraclavicular nodes N3b – Ipsilateral internal mammary nodes N3c – Ipsilateral supraclavicular nodes Distant Metastases (M) M0: No clinical or radiographic evidence of distant metastases M0(i+): Molecularly or microscopically detected tumor cells in circulating blood, bone marrow or non-regional nodal tissue, no larger than 0.2 mm, and without clinical or radiographic evidence or symptoms or signs of metastases, and which, perhaps counter-intuitively, does not change the stage grouping, as staging for in M0(i+) is done according to the T and N values M1: Distant detectable metastases as determined by classic clinical and radiographic means, and/or metastasis that are histologically larger than 0.2 mm. Overall stage A combination of T, N and M, as follows: Stage 0: Tis Stage I: T1N0 Stage II: T2N0, T3N0 T0N1, T1N1, or T2N1 Stage III: Invasion into skin and/or ribs, matted lymph nodes, T3N1, T0N2, T1N2, T2N2, T3N2, AnyT N3, T4 any N, locally advanced breast cancer Stage IV: M1, advanced breast cancer

Further information: Evaluation of tumors

Grading

The Nottingham system is recommended for breast cancer grading. The Nottingham system is also called the Bloom–Richardson–Elston system (BRE), or the Elston-Ellis modification of the Scarff-Bloom-Richardson grading system. It grades breast carcinomas by adding up scores for tubule formation, nuclear pleomorphism, and mitotic count, each of which is given 1 to 3 points. The scores for each of these three criteria are then added together to give an overall final score and corresponding grade as follows.

Tubule formation

By definition, tubule formation in classic invasive lobular carcinoma is scored as 3.

Nuclear pleomorphism

Such as nuclei being larger, darker, or irregular/pleomorphic. Note: The cancer areas having cells with the greatest atypia should be evaluated.

• 1 point: nuclei with minimal or mild variation in size and shape
• 2 points: nuclei with moderate variation in size and shape
• 3 points: nuclei with marked variation in size and shape

• 

  Invasive lobular carcinoma with moderate nuclear pleomorphism.

Mitotic count

Mitosis appearances in breast cancer

Mitotic figures are counted only at the periphery of the tumor, and counting should begin in the most mitotically active areas, and in at least 10 high-power fields (HPFs). If you know that the area of your high power field is about 0.2mm², then you may score mitotic count as follows:

• 1 point: ≤7 mitoses per 10 HPFs
• 2 points: 8 to 14 mitoses per 10 HPFs
• 3 points: ≥15 mitoses per 10 HPFs

If you have a significant different HPF area or you are not sure, count 10 HPFs and calculate the number of mitoses per mm² (Further information: Evaluation#Counts per mm2 ):

• 1 point: ≤3 mitoses per mm²
• 2 points: 4 to 7 mitoses per mm²
• 3 points: ≥7 mitoses per mm²

A table of counts for various HPF sizes is available at the College of American Pathologists. [1] (Page 22)

Overall grade

The scores for each of these three criteria are added together to give a final overall score and a corresponding grade as follows:

• 3-5 Grade 1 tumor (well-differentiated). Best prognosis.
• 6-7 Grade 2 tumor (moderately differentiated). Medium prognosis.
• 8-9 Grade 3 tumor (poorly differentiated). Worst prognosis.

Microcalcifications

Microcalcifications of non-neoplastic breast glands.

If invasive ductal carcinoma is seen, make at least a low power screening for microcalcifications (to correlate with imaging), but there's no need to look carefully (as tiny microcalcifications would unlikely correlate with imaging anyways).

Immunohistochemistry

Look at local protocols for what immunohistochemistry tests and other biomarker test need to be tested for each case of invasive breast cancer, or what needs to be retested for subsequent excisions at the primary site or at metastatic sites.

Ki-67 index

Ki-67 in an invasive breast cancer: cancer nuclei are stained (brown). There is tumor cell positivity in 70% of the cells (Ki-67 labelling index = 70%).

To count as Ki-67 positive, a nucleus should:
- Not be located in stroma.
- Be at least half within the field of view.
- Be large enough.
Otherwise, even weakly positive nuclei count as positive.

Ki-67 index is mainly relevant in those with stage T1-T2, N0-N1, to determine if chemotherapy is needed (if Ki67 is >30% rather than <5%).

Ki-67 index is most feasibly quantified by a hot spot method, Hot spots are areas in which Ki-67 staining is particularly higher relative to the adjacent tumor areas. Usually, the invasive edge of a tumor is a hot spot. When a tumor had several hot spots, the “hottest” spot is selected. Aim to count at least 500 cells in each case, but this is not always possible in cases with low tumor cell density and small tumor size. Also aim to include at least three high-power (×40 objective) fields. Count a nucleus as “positive” if there is any definite brown staining in the nucleus of an invasive breast cancer cell, above the surrounding background in the cytoplasm and extracellular matrix. If a comparisons must be made between core biopsies and sections from an excision, evaluation of the latter should be across the whole tumor. Only nuclear staining counts. Staining intensity of a positive nucleus is not relevant.

HER2

HER2 can initially be evaluated by immunohistochemistry (IHC) or fluorescence in situ hybridization (FISH). If IHC is performed first and is borderline/equivocal, then FISH is recommended. If FISH is performed first and indicates that further workup is required, then IHC may be the performed as per established algorithms.

HER2 immunohistochemistry

Look at different parts of the tumor, and evaluate the area(s) with most staining. When negative of faint staining is seen, evaluate at high magnification.

Immunohistochemistry

Score	Pattern	Status
0	Either: No staining observed. Incomplete membrane staining that is faint or barely perceptible and within ≤10% of the invasive tumor cells	HER2 negative (not present)
1+	Incomplete membrane staining that is faint or barely perceptible and within >10% of the invasive tumor cells.
2+	Weak to moderate complete membrane staining observed in >10% of tumor cells.	Borderline/Equivocal
3+	Circumferential membrane staining that is complete, intense, and in >10% of tumor cells.	HER2 positive

Micrographs showing each score:

• 

  0

• 

  1+

• 

  2+

• 

  3+

HER2 FISH

HER2 FISH usually uses chromosome enumeration probe 17 (CEP17) to count the amount of chromosomes. Hence, the HER2/CEP17 ratio reflects any amplification of HER2 as compared to the number of chromosomes.

To prepare a slide for HER2 testing, you may need to choose a paraffin-embedded and mark the resulting slide so that you or whoever interprets it knows where to look for the target tumor cells. When there are multiple blocks of the same case, choose the the one with most tumor. (If a block has undergone sectioning for immunohistochemistry (such as ER, PR and/or Ki67) make sure that you have a new H&E slide at a level next to the one to be used for FISH, so that they will correlate better.) In cases of both invasive and in situ carcinoma in the same specimen, mark all invasive carcinoma (also for crushed tissue or with other artifacts) but not the in situ carcinoma. Also mark a small area of normal tissue as an internal control. If possible, it should be a bit away from the tumor, even if only consisting of fatty tissue.

To interpret a HER2 FISH study, first perform a quality control check of the slide as per manufacturer and/or local protocol (generally including checking for proper signals from a control specimen). In cases of both invasive and in situ carcinoma in the same specimen, only score the invasive cells. The signals of 20 cells are usually counted. Also focus up and down on each nucleus to find all signals therein.

• 

  Identify the relevant tumor cells. It can be made easier by comparing to an H&E stained slide.

• 

  This cell displays 2 signals of HER2 (red) and 3 signals of CEP17 (green)

• 

  Two signals that are closer to each other than the signal diameter count as one.

• 

  One of these signals is too faint, and is presumably debris.

• 

  Cells with only one type of signal are excluded from the count.

• 

  Overlapping cells are also excluded from the count.

• 

  A yellow signal cunts as one red and one green (which are overlapping)

If a cytotechnologist has already performed a count, you do not have to recount, but make sure the count is reasonable regarding what you see. In any case, also look around for any obvious tumor heterogeneity in HER2 signals.

• 
• 

  Algorithm for the evaluation of HER2 on fluorescence in situ hybridization (FISH). See source article in cases where additional workup is indicated.

If the HER2/CEP17 ratio is borderline (1.8-2.2), count an additional 20 nuclei and recalculate a ratio for the total of 40 nuclei.

Classification of HER2 by fluorescence in situ hybridization (FISH)

		HER2/CEP17 ratio
		≥2.0	<2.0
Average HER2 copy number per cell	≥4.0	HER2 positive	Additional work-up required
	<4.0	Additional work-up required	HER2 negative

If the initial HER2 result is negative for a needle biopsy of a primary breast cancer, a new HER2 test may be performed on the subsequent breast excision.

Estrogen and progesterone receptors

Generally perform immunohistochemistry for estrogen and progesterone receptors and calculate the percentage of positive tumor cells.

• 

  Progesterone recepotor, moderate intensity, 61-70% of nuclei.

Neoadjuvant cases

If not already stated, look for clues that neoadjuvant treatment has been given, that is, when the patient has received chemotherapy, endocrine therapy and/or radiotherapy before the excision. Look more thoroughly for it if the duration between a previous biopsy and subsequent excision is longer than usual. It's usually about a month.

In neoadjuvant cases , perform:

• Measurement of the tumor bed which generally manifests as a fibroelastic area.
• Classification of residual cancer, for which there are multiple systems, mainly Residual Cancer Burden (RCB) and the American Joint Committee on Cancer post-neoadjuvant therapy staging system (yAJCC).

Further information: Evaluation of tumors

Report

Breast excision

• Tumor size, if not already given from gross report. Give 3 dimensions or greatest dimension.
• Histopathologic subtype if apparent, but "invasive carcinoma" is acceptable.
• Stage
• Grade, preferably by overall BRE grade. Optionally, give scores for the components thereof.

• Extent of any angiolymphatic invasion.

• Margins of resection, as closest distance from carcinoma to margin in mm or cm or "tumor on ink"/"carcinoma is present on margin". ((If applicable, also specify as "close margins" (no tumor on ink but <2 mm), or "negative margins" (≥2 mm).))
• Results of any immunohistochemistry and other tests

• HER2 as a score or status.
• Ki-67, preferably as labeling index

Example:

Breast excision with 70 x 55 x 18 mm ductal invasive breast cancer. Nottingham grade II. Estrogen receptor positive, progesterone receptor negative, HER2 receptor score 0, Ki-67 index 17%, T1b. Radically removed.

Needle or core biopsy

• Histopathologic subtype if apparent, but "invasive carcinoma" is acceptable.
• Results of any immunohistochemistry and other tests, as per excision
• Presence of absence of lymphatic and/or vascular invasion
• Optionally: Provisional grading. Grading can alternatively be deferred to excision.
• State if studies are deferred for a later excision sample

For cancers, generally include a synoptic report, such as per College of American Pathologists (CAP) protocols at cap.org/protocols-and-guidelines.

synoptic report example

Tumor type:  invasive ductal carcinoma with micropapillary pattern

Tumor size:  greatest microscopic measurement of invasive carcinoma in positive core(s)):  0.7 cm

In-situ component: no

Microscopic grading (Nottingham modification of the Bloom-Richardson system):

• Only applies to infiltrating ductal and lobular carcinoma:  

Tubule formation: Little or none (score =3)

Nuclear pleomorphism: Marked variation in size, nucleoli, chromatin clumping, etc. (score =3)

Mitotic count : Less than 6 mitoses per 10 hpf (score =1)

Composite score: 7 points  (applies to infiltrating ductal and lobular carcinoma only)

Histologic grade: Grade II: 6-7  points

Nuclear grade: grade 3

Microcalcifications: Present in non-neoplastic tissue

Lymphocytic host response: absent

Necrosis:  absent

Blood vessel invasion: absent

Histopathology of lymphatic invasion by carcinoma, H&E stain

Lymphatic and/or vascular invasion: absent

Skin involvement: not applicable

Results of immunohistochemical stains for prognostic markers (as per original report):

Estrogen Receptor (ER) Status:  Positive (greater than 10% of cells demonstrate nuclear positivity)

Percentage of Cells with Nuclear Positivity:  91-100%

Average Intensity of Staining:  Strong

Progesterone Receptor (PgR) Status:  Positive

Percentage of Cells with Nuclear Positivity:  51-60%

Average Intensity of Staining:  Strong, moderate and weak

HER-2 by IHC:  2+ / Equivocal

REFLEX HER-2 FISH TEST:  Nonamplificed (ratio 1.5;  3.5 Her-2 signals/cell)

Ki-67:

Percentage of Cells with Nuclear Positivity: 43%

Primary Antibody: MIB1

Cold Ischemia and Fixation Times: 3 minutes

Fixation Time (hours): 14 hours and 33 minutes

Fixative:  formalin

Main page

• Main page of Patholines