Definition/General
Introduction:
Minimal deviation adenocarcinoma (MDA) of the breast is an extremely rare variant of well-differentiated adenocarcinoma, analogous to adenoma malignum of the cervix
It is characterized by deceptively bland, well-formed glands that deeply infiltrate the stroma.
Origin:
It is thought to arise from the terminal duct-lobular unit (TDLU).
Classification:
It is a rare variant of well-differentiated invasive ductal carcinoma.
Epidemiology:
Extremely rare, with only a few case reports in the literature
It can be associated with Peutz-Jeghers syndrome.
Clinical Features
Presentation:
Presents as a palpable breast mass
The clinical and radiological features are non-specific.
Symptoms:
A painless breast lump is the most common symptom.
Risk Factors:
Association with Peutz-Jeghers syndrome has been reported.
Screening:
Usually diagnosed after investigation of a palpable mass
Mammographic and ultrasound findings are non-specific.
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Gross Description
Appearance:
A firm, ill-defined, gray-white mass.
Characteristics:
The tumor may have a rubbery or firm consistency.
Size Location:
Can occur anywhere in the breast.
Multifocality:
Rare.
Microscopic Description
Histological Features:
The tumor is composed of haphazardly arranged, well-formed glands that deeply infiltrate the stroma
The glands are lined by a single layer of deceptively bland cuboidal or columnar cells
There is a prominent desmoplastic stromal reaction.
Cellular Characteristics:
The tumor cells show minimal cytological atypia, with small, uniform nuclei and inconspicuous nucleoli
Mitotic activity is low
Despite the bland appearance, the infiltrative nature and absence of a myoepithelial layer are key to the diagnosis.
Architectural Patterns:
The key feature is the deep, infiltrative growth of bland-looking glands.
Grading Criteria:
This is a well-differentiated (Grade 1) carcinoma.
Immunohistochemistry
Positive Markers:
The tumor cells are positive for cytokeratins (e.g., CK7)
They are typically ER and PR positive.
Negative Markers:
HER2 is usually negative
Myoepithelial markers (e.g., p63, calponin) are absent around the infiltrating glands.
Diagnostic Utility:
IHC is crucial to demonstrate the absence of a myoepithelial layer to confirm invasion
Hormone receptor status is important for therapy.
Molecular Subtypes:
Most are of the Luminal A molecular subtype.
Molecular/Genetic
Genetic Mutations:
Association with germline mutations in the STK11 gene (Peutz-Jeghers syndrome) has been reported.
Molecular Markers:
No specific molecular markers are routinely used for diagnosis.
Prognostic Significance:
Despite its well-differentiated appearance, MDA can have an aggressive course with a risk of lymph node and distant metastasis
The prognosis is better than for high-grade carcinomas but worse than for tubular carcinoma.
Therapeutic Targets:
Treatment is primarily surgical
Endocrine therapy is often used due to the high rate of ER positivity.
Differential Diagnosis
Similar Entities:
Tubular carcinoma
Sclerosing adenosis
Radial scar
Microglandular adenosis.
Distinguishing Features:
Tubular carcinoma has more angulated tubules and apical snouts
Sclerosing adenosis and radial scar are benign lesions that retain a myoepithelial layer
Microglandular adenosis is ER-negative and S100-positive.
Diagnostic Challenges:
The main challenge is distinguishing MDA from benign sclerosing lesions due to its bland cytology
The deep infiltrative pattern and absence of myoepithelial cells are key distinguishing features.
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]