Definition/General
Introduction:
Apocrine metaplasia is a benign breast lesion characterized by the transformation of the ductal or lobular epithelium into cells with apocrine features
It is an extremely common finding and is a component of fibrocystic changes.
Origin:
It arises from the terminal duct-lobular unit (TDLU)
It is a metaplastic process, meaning a change from one mature cell type to another.
Classification:
Apocrine metaplasia is classified as a benign, non-proliferative breast lesion
When it is associated with hyperplasia or atypia, it is classified accordingly (e.g., apocrine hyperplasia, apocrine atypia).
Epidemiology:
It is a very common finding, present in a large proportion of adult female breasts
It is most common in the perimenopausal period.
Clinical Features
Presentation:
Apocrine metaplasia is an incidental microscopic finding and is not associated with a palpable mass or specific mammographic findings
It is often seen in breast tissue surrounding cysts.
Symptoms:
Asymptomatic.
Risk Factors:
There are no well-established risk factors.
Screening:
Apocrine metaplasia is a microscopic finding and not specifically screened for.
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Gross Description
Appearance:
There are no specific gross findings for apocrine metaplasia
It is often associated with cysts, which may be visible grossly.
Characteristics:
Gross findings are not specific for this microscopic diagnosis.
Size Location:
Gross findings are not specific for this microscopic diagnosis.
Multifocality:
Often multifocal.
Microscopic Description
Histological Features:
The ducts and lobules are lined by large polygonal cells with abundant, granular, eosinophilic cytoplasm and distinct cell borders
The cells often show apical snouts or decapitation secretions.
Cellular Characteristics:
The nuclei are typically round and vesicular, with a single, prominent, centrally located, eosinophilic nucleolus
Cytological atypia is absent in simple apocrine metaplasia.
Architectural Patterns:
The cells form a single layer lining the ducts and acini
Papillary formations can be seen.
Grading Criteria:
This is a benign lesion.
Immunohistochemistry
Positive Markers:
The cells are positive for Gross Cystic Disease Fluid Protein-15 (GCDFP-15) and Androgen Receptor (AR)
They are typically negative for ER and PR.
Negative Markers:
Usually negative for ER and PR
HER2 can be expressed but is not amplified.
Diagnostic Utility:
IHC is not usually necessary for diagnosis but can be used to confirm apocrine differentiation (GCDFP-15, AR).
Molecular Subtypes:
Molecular subtyping is not relevant for this benign condition.
Molecular/Genetic
Genetic Mutations:
Apocrine metaplasia can show some genetic alterations, such as loss of heterozygosity, but these are not routinely tested for.
Molecular Markers:
No specific molecular markers are routinely used for diagnosis.
Prognostic Significance:
Simple apocrine metaplasia is not associated with an increased risk of developing invasive breast cancer.
Therapeutic Targets:
No treatment is required.
Differential Diagnosis
Similar Entities:
Apocrine hyperplasia
Apocrine atypia
Apocrine DCIS
Apocrine carcinoma.
Distinguishing Features:
Apocrine hyperplasia shows a multilayered proliferation of apocrine cells
Apocrine atypia and carcinoma show increasing degrees of cytological atypia and architectural complexity.
Diagnostic Challenges:
The main challenge is to assess for the presence of atypia, which can be subjective.
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]