Definition/General

Introduction:
-Plasma cell mastitis is a benign inflammatory condition of the breast characterized by a prominent plasma cell infiltrate in the periductal stroma
-It is considered a form of chronic mastitis and is often associated with duct ectasia.
Origin: It is thought to be a reaction to the contents of dilated ducts (duct ectasia).
Classification: It is a subtype of chronic mastitis.
Epidemiology: It is most common in middle-aged and older women.

Clinical Features

Presentation:
-Presents as a palpable, ill-defined, subareolar mass
-Nipple retraction can occur, mimicking carcinoma.
Symptoms: A painless or mildly tender breast lump is the most common symptom.
Risk Factors: Duct ectasia is the main risk factor.
Screening: Mammography can show a spiculated mass or architectural distortion.

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Gross Description

Appearance:
-An ill-defined, firm, gray-white area of induration.
Characteristics: The tissue is fibrotic.
Size Location: Usually located in the subareolar region.
Multifocality: Can be multifocal.

Microscopic Description

Histological Features:
-The key feature is a dense, periductal inflammatory infiltrate composed predominantly of mature plasma cells
-Lymphocytes and histiocytes are also present
-It is often seen in the context of duct ectasia.
Cellular Characteristics: Sheets of plasma cells with eccentric nuclei and clock-face chromatin are characteristic.
Architectural Patterns: A periductal inflammatory infiltrate is characteristic.
Grading Criteria: This is a benign inflammatory process.

Immunohistochemistry

Positive Markers:
-The plasma cells are polyclonal, showing a mixture of kappa and lambda light chain expression.
Negative Markers: Not applicable.
Diagnostic Utility: IHC for kappa and lambda light chains can be used to confirm the polyclonal nature of the plasma cell infiltrate and to rule out a plasmacytoma.
Molecular Subtypes: Not applicable.

Molecular/Genetic

Genetic Mutations: Not applicable.
Molecular Markers: No specific molecular markers are routinely used for diagnosis.
Prognostic Significance: This is a benign condition and is not associated with an increased risk of breast cancer.
Therapeutic Targets: No treatment is required unless it forms a mass that needs to be distinguished from carcinoma.

Differential Diagnosis

Similar Entities:
-Invasive carcinoma
-Plasmacytoma.
Distinguishing Features:
-Invasive carcinoma has malignant epithelial cells
-A plasmacytoma is a monoclonal proliferation of plasma cells.
Diagnostic Challenges:
-The main challenge is to distinguish it from a plasmacytoma, which is rare in the breast
-Light chain IHC is key.
Rare Variants: Not applicable.

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]