Definition/General
Introduction:
Microglandular adenosis (MGA) is a rare benign proliferative breast lesion characterized by a haphazard proliferation of small, round, open glands
A key feature is the absence of a myoepithelial layer, which can cause it to be mistaken for invasive carcinoma.
Origin:
It arises from the terminal duct-lobular unit (TDLU).
Classification:
MGA is classified as a benign proliferative breast lesion
It can be associated with atypia (atypical MGA) and can be a precursor to carcinoma arising in MGA.
Epidemiology:
It is a rare lesion, most often found in women in their 40s and 50s.
Clinical Features
Presentation:
MGA can present as a palpable mass or be an incidental finding on a biopsy performed for other reasons.
Symptoms:
Usually asymptomatic, but can form a palpable lump.
Risk Factors:
There are no well-established risk factors.
Screening:
Mammographic findings are non-specific and can include a mass, architectural distortion, or calcifications.
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Gross Description
Appearance:
It can form a firm, ill-defined, yellow-tan mass.
Characteristics:
The size is variable.
Size Location:
Can occur anywhere in the breast.
Multifocality:
Can be multifocal.
Microscopic Description
Histological Features:
The lesion is composed of a proliferation of small, round, uniform glands infiltrating the stroma and adipose tissue
The glands have open lumina that often contain eosinophilic, colloid-like secretions
The key feature is the absence of a myoepithelial layer.
Cellular Characteristics:
The cells are cuboidal with scant, eosinophilic or vacuolated cytoplasm
The nuclei are small, round, and uniform with inconspicuous nucleoli
Mitotic activity is low.
Architectural Patterns:
The glands are haphazardly arranged and infiltrate the stroma in a pattern that can mimic tubular carcinoma.
Grading Criteria:
This is a benign lesion
Atypical MGA shows increased cytological atypia.
Immunohistochemistry
Positive Markers:
The epithelial cells are positive for S100 and low molecular weight cytokeratins
They are also positive for collagen IV and laminin, which highlights a continuous basement membrane around the glands.
Negative Markers:
The cells are negative for ER, PR, and HER2
Importantly, they are negative for myoepithelial markers (e.g., p63, calponin), which is a diagnostic pitfall.
Diagnostic Utility:
IHC is crucial for diagnosis
The combination of S100 positivity, ER negativity, and absence of myoepithelial markers is characteristic of MGA and helps distinguish it from tubular carcinoma.
Molecular Subtypes:
Molecular subtyping is not relevant for this benign condition.
Molecular/Genetic
Genetic Mutations:
Not well characterized.
Molecular Markers:
No specific molecular markers are routinely used for diagnosis.
Prognostic Significance:
MGA is a risk factor for breast cancer
It can be a precursor to a rare type of triple-negative carcinoma that arises in MGA.
Therapeutic Targets:
Surgical excision is recommended to exclude associated atypia or carcinoma.
Differential Diagnosis
Similar Entities:
Tubular carcinoma
Sclerosing adenosis.
Distinguishing Features:
Tubular carcinoma is ER-positive and S100-negative
Sclerosing adenosis has a myoepithelial layer
The IHC profile of MGA (S100+, ER-, myoepithelial markers-) is very helpful in the differential diagnosis.
Diagnostic Challenges:
The main challenge is distinguishing MGA from tubular carcinoma, especially on a small biopsy
The absence of a myoepithelial layer in a benign lesion is a major diagnostic pitfall.
Rare Variants:
Atypical MGA is a variant with increased cytological atypia.
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]