Definition/General
Introduction:
Granulomatous mastitis is a rare chronic inflammatory disease of the breast characterized by the formation of non-caseating granulomas
It can be idiopathic (idiopathic granulomatous mastitis or IGM) or secondary to specific causes.
Origin:
The cause of IGM is unknown, but it is thought to be an autoimmune reaction to breast ductal contents
Secondary causes include infections (e.g., tuberculosis, fungal infections), sarcoidosis, and foreign body reactions.
Classification:
It is classified as a benign inflammatory breast condition.
Epidemiology:
IGM typically affects young, parous women, often within a few years of pregnancy
It is more common in women of Hispanic and Asian descent.
Clinical Features
Presentation:
Presents as a firm, tender, palpable mass, often associated with skin inflammation, ulceration, or abscess formation
It can mimic breast carcinoma.
Symptoms:
A painful breast lump is the most common symptom
Skin changes and nipple retraction can occur.
Risk Factors:
History of pregnancy and lactation is a common feature
Association with Corynebacterium infection has been reported.
Screening:
Mammography and ultrasound findings are non-specific and can be suspicious for malignancy.
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Gross Description
Appearance:
An ill-defined, firm, indurated area with a yellow-tan cut surface
Abscess cavities may be present.
Characteristics:
The lesion can be extensive and involve a large portion of the breast.
Size Location:
Size is variable.
Multifocality:
Can be multifocal.
Microscopic Description
Histological Features:
The key feature is the presence of non-caseating granulomas centered on the breast lobules
The granulomas are composed of epithelioid histiocytes, multinucleated giant cells, lymphocytes, and plasma cells
A mixed inflammatory infiltrate with neutrophils is also common, and microabscesses can be seen.
Cellular Characteristics:
The inflammatory infiltrate is mixed
The granulomas are typically non-necrotizing.
Architectural Patterns:
A lobulocentric inflammatory process is characteristic.
Grading Criteria:
This is a benign inflammatory process.
Immunohistochemistry
Positive Markers:
Not typically required for diagnosis.
Negative Markers:
Not typically required for diagnosis.
Diagnostic Utility:
IHC is not used for diagnosis
Special stains for microorganisms (e.g., Ziehl-Neelsen for acid-fast bacilli, GMS for fungi) are important to rule out an infectious cause.
Molecular Subtypes:
Molecular subtyping is not relevant for this benign condition.
Molecular/Genetic
Genetic Mutations:
This is a benign condition and is not associated with specific genetic mutations.
Molecular Markers:
No specific molecular markers are routinely used for diagnosis.
Prognostic Significance:
This is a benign condition, but it can have a chronic, relapsing course
It is not associated with an increased risk of breast cancer.
Therapeutic Targets:
Treatment is controversial and can include observation, corticosteroids, immunosuppressants, and surgery.
Differential Diagnosis
Similar Entities:
Invasive carcinoma
Tuberculous mastitis
Sarcoidosis
Fat necrosis.
Distinguishing Features:
Invasive carcinoma is composed of malignant epithelial cells
Tuberculous mastitis has caseating granulomas and positive AFB stain
Sarcoidosis is a systemic disease with "naked" granulomas
Fat necrosis has foamy macrophages and anucleated adipocytes.
Diagnostic Challenges:
The main challenge is to exclude an infectious cause and to distinguish it from carcinoma, which it can mimic clinically and radiologically.
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]