Definition/General
Introduction:
Primary squamous cell carcinoma (SCC) of the breast is an extremely rare and aggressive malignancy
It is a type of metaplastic carcinoma where the entire tumor is composed of malignant squamous cells
The diagnosis requires the exclusion of metastasis from another primary site.
Origin:
The origin is debated, but it is thought to arise from the metaplastic transformation of breast ductal epithelium or from the epidermis of the nipple.
Classification:
It is classified as a subtype of metaplastic breast carcinoma
It can be keratinizing or non-keratinizing.
Epidemiology:
Extremely rare, accounting for less than 0.1% of all invasive breast cancers
It typically affects older women.
Clinical Features
Presentation:
Presents as a large, rapidly growing, palpable breast mass
The mass is often cystic and can be associated with skin ulceration or abscess formation.
Symptoms:
A painless, large breast lump is the most common symptom
Skin changes are common.
Risk Factors:
No specific risk factors are well-established
It can be associated with chronic inflammation or abscesses.
Screening:
Usually presents as a palpable mass
Mammographic findings are non-specific, often showing a complex cystic mass.
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Gross Description
Appearance:
A large, often cystic mass with a thick, irregular wall
The cyst may contain necrotic material
Solid areas are firm and gray-white.
Characteristics:
The tumor is often large at diagnosis
Necrosis and cystic degeneration are common features.
Size Location:
Can occur anywhere in the breast.
Multifocality:
Rare.
Microscopic Description
Histological Features:
The tumor is composed of sheets and nests of malignant squamous cells with intercellular bridges and keratinization
A glandular component is absent.
Cellular Characteristics:
The tumor cells are large and polygonal with abundant eosinophilic cytoplasm and large, hyperchromatic, irregular nuclei
Mitotic activity is high.
Architectural Patterns:
The growth pattern is infiltrative
Keratin pearls are a characteristic feature of well-differentiated tumors.
Grading Criteria:
These are considered high-grade tumors.
Immunohistochemistry
Positive Markers:
The tumor cells are positive for squamous markers such as p63, CK5/6, and CK14
They are also positive for broad-spectrum cytokeratins.
Negative Markers:
Typically triple-negative (ER, PR, and HER2 negative)
Negative for glandular markers like CK7 in most cases.
Diagnostic Utility:
IHC is essential to confirm squamous differentiation and to exclude other tumor types.
Molecular Subtypes:
Most are classified as triple-negative/basal-like breast cancer.
Molecular/Genetic
Genetic Mutations:
The molecular genetics are not well characterized but often involve TP53 mutations.
Molecular Markers:
No specific molecular markers are routinely used for diagnosis.
Prognostic Significance:
The prognosis is generally poor, worse than that of conventional adenocarcinoma NST
It has a high rate of local and distant recurrence.
Therapeutic Targets:
Treatment is primarily surgical
As a triple-negative cancer, it does not respond to hormonal or HER2-targeted therapy
Platinum-based chemotherapy is often used.
Differential Diagnosis
Similar Entities:
Metastatic SCC from another site (e.g., lung, cervix)
Metaplastic carcinoma with squamous differentiation
Adenosquamous carcinoma.
Distinguishing Features:
Excluding a metastasis is crucial and requires a thorough clinical workup
Metaplastic carcinoma with squamous differentiation and adenosquamous carcinoma will have a glandular component, which is absent in pure SCC.
Diagnostic Challenges:
The main challenge is to confirm a primary breast origin
The presence of an in situ squamous component would be definitive but is rarely seen.
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]