Definition/General
Introduction:
Invasive micropapillary carcinoma (IMPC) is a rare and aggressive variant of invasive ductal carcinoma characterized by a distinctive growth pattern of small, hollow, morula-like clusters of tumor cells within clear stromal spaces
It has a high propensity for lymphovascular invasion and lymph node metastasis.
Origin:
It arises from the ductal epithelium.
Classification:
It is a subtype of invasive ductal carcinoma
It can be pure or mixed with other types of invasive carcinoma.
Epidemiology:
It is rare, accounting for less than 2% of all invasive breast cancers
It typically affects postmenopausal women.
Clinical Features
Presentation:
Presents as a palpable, firm, irregular mass.
Symptoms:
A painless breast lump is the most common symptom.
Risk Factors:
The risk factors are similar to those for other types of breast cancer.
Screening:
Mammography shows a spiculated, high-density mass, often with calcifications.
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Gross Description
Appearance:
A firm, gray-white, infiltrative mass.
Characteristics:
The size is variable.
Size Location:
Can occur anywhere in the breast.
Multifocality:
Can be multifocal.
Microscopic Description
Histological Features:
The tumor is composed of small, cohesive clusters of cells that lie within clear, empty stromal spaces, mimicking lymphatic vessels
The cell clusters have a characteristic "inside-out" or reverse polarity, with the apical surface facing the stroma
There are no true fibrovascular cores.
Cellular Characteristics:
The cells are typically high-grade, with pleomorphic nuclei and prominent nucleoli
Mitotic activity is often high.
Architectural Patterns:
The micropapillary pattern is the key feature
It is often associated with extensive lymphovascular invasion.
Grading Criteria:
These are typically high-grade tumors.
Immunohistochemistry
Positive Markers:
The tumor cells are positive for cytokeratins and are often ER-positive
The reverse polarity can be highlighted by staining for EMA, which shows a characteristic "inside-out" pattern.
Negative Markers:
HER2 is overexpressed in a subset of cases.
Diagnostic Utility:
EMA staining can be helpful to demonstrate the reverse polarity
D2-40 can be used to highlight true lymphatic invasion.
Molecular Subtypes:
Most are of the luminal subtype.
Molecular/Genetic
Genetic Mutations:
Not well characterized.
Molecular Markers:
No specific molecular markers are routinely used for diagnosis.
Prognostic Significance:
IMPC has a poor prognosis due to its high rate of lymphovascular invasion and lymph node metastasis, even when the tumor is small.
Therapeutic Targets:
Treatment is similar to that of conventional breast cancer, based on ER and HER2 status.
Differential Diagnosis
Similar Entities:
Adenocarcinoma with extensive lymphovascular invasion
Papillary carcinoma.
Distinguishing Features:
The clear spaces in IMPC are artefactual and are not true lymphatic vessels (they are negative for D2-40)
Papillary carcinomas have true fibrovascular cores.
Diagnostic Challenges:
The main challenge is recognizing the characteristic micropapillary pattern and distinguishing it from extensive lymphovascular invasion.
Rare Variants:
There are no specific rare variants.
Sample Pathology Report
Template Format
Sample Pathology Report
Complete Report: This is an example of how the final pathology report should be structured for this condition.
Specimen Information
[specimen type], measuring [size] cm in greatest dimension
Diagnosis
[diagnosis name]
Classification
Classification: [classification system] [grade/type]
Histological Features
Shows [architectural pattern] with [nuclear features] and [mitotic activity]
Size and Extent
Size: [X] cm, extent: [local/regional/metastatic]
Margins
Margins are [involved/uninvolved] with closest margin [X] mm
Lymphovascular Invasion
Lymphovascular invasion: [present/absent]
Lymph Node Status
Lymph nodes: [X] positive out of [X] examined
Special Studies
IHC: [marker]: [result]
Molecular: [test]: [result]
[other study]: [result]
Final Diagnosis
Final diagnosis: [complete diagnosis]