Definition/General
Introduction:
Acinic cell carcinoma (ACC) of the breast is an extremely rare subtype of triple-negative breast cancer that is histologically similar to ACC of the salivary glands
It is characterized by malignant epithelial cells with serous acinar differentiation.
Origin:
The cell of origin is thought to be from the terminal duct-lobular unit (TDLU), with differentiation towards acinar cells.
Classification:
It is classified as a rare subtype of invasive breast carcinoma
It is part of the spectrum of salivary gland-like tumors of the breast.
Epidemiology:
Extremely rare, with only a small number of cases reported
It can affect a wide age range of women.
Clinical Features
Presentation:
Presents as a palpable breast mass
The clinical and radiological features are non-specific and can mimic other breast carcinomas.
Symptoms:
A painless breast lump is the most common symptom.
Risk Factors:
No specific risk factors are known due to its rarity.
Screening:
Usually diagnosed after investigation of a palpable mass
Mammographic and ultrasound findings are non-specific.
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Gross Description
Appearance:
Typically a well-circumscribed, firm, gray-white mass.
Characteristics:
Size is variable
Necrosis is uncommon.
Size Location:
Can occur anywhere in the breast.
Multifocality:
Rare.
Microscopic Description
Histological Features:
The tumor is composed of cells with abundant, granular, amphophilic, or eosinophilic cytoplasm, resembling salivary gland acinar cells
The cells are arranged in solid, microcystic, or glandular patterns.
Cellular Characteristics:
The tumor cells have round to oval nuclei with inconspicuous nucleoli
The cytoplasm is granular due to the presence of zymogen-like granules, which are PAS-positive and diastase-resistant.
Architectural Patterns:
Solid sheets, nests, and acinar structures are common.
Grading Criteria:
Most cases are considered low to intermediate grade.
Immunohistochemistry
Positive Markers:
The tumor cells are positive for amylase, lysozyme, and chymotrypsin, confirming acinar differentiation
They are also positive for S100 and DOG1
They are typically positive for cytokeratins.
Negative Markers:
Characteristically triple-negative (ER, PR, and HER2 negative).
Diagnostic Utility:
IHC is crucial for diagnosis, especially the stains for acinar differentiation
It is important to distinguish from other triple-negative breast cancers.
Molecular Subtypes:
Classified as triple-negative.
Molecular/Genetic
Genetic Mutations:
The molecular genetics are not well characterized due to the rarity of the tumor
Some cases show rearrangements of the ETV6 gene, similar to secretory carcinoma.
Molecular Markers:
No specific molecular markers are routinely used for diagnosis.
Prognostic Significance:
The prognosis is generally considered to be favorable, better than that of conventional triple-negative breast cancer
However, recurrences and metastases can occur.
Therapeutic Targets:
Treatment is primarily surgical
As it is a triple-negative cancer, it does not respond to hormonal or HER2-targeted therapy
The role of chemotherapy is not well-defined.
Differential Diagnosis
Similar Entities:
Secretory carcinoma
Apocrine carcinoma
Metastatic acinic cell carcinoma from the salivary gland.
Distinguishing Features:
Secretory carcinoma is S100 positive but has eosinophilic secretions and the ETV6-NTRK3 fusion
Apocrine carcinoma has more prominent nucleoli and is positive for AR and GCDFP-15
Metastatic ACC from the salivary gland must be excluded clinically.
Diagnostic Challenges:
The main challenge is its rarity and distinguishing it from other breast tumors with granular cytoplasm
A high index of suspicion and appropriate IHC are key.
Rare Variants:
The entire entity is a rare variant.
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]