Surgical Pathology Criteria

Fibroadenoma of the Breast

Differential Diagnosis

(Adult Type) Fibroadenoma Juvenile Fibroadenoma
Hypocellular to variably cellular stroma Uniformly hypercellular stroma

 

Fibroadenoma Low Grade Phyllodes Tumor
Lacks significant stromal hypercellularity Hypercellular stroma is prominent
No stromal overgrowth May have stromal overgrowth
No leaf-like architecture Prominent leaf-like architecture
No condensation around ducts Stromal condensation around ducts
Does not infiltrate May infiltrate surrounding breast
The histologic border between these two is not always sharp

 

Fibroadenoma High Grade Phyllodes Tumor
Lacks significant stromal hypercellularity Hypercellular stroma
No stromal overgrowth Stromal overgrowth
No stromal atypia Pleomorphic stromal cells
Stromal mitotic rate < 3/hpf Elevated stromal mitotic rate, usually >4-5 per 10 hpf, abnormal forms may be found
Does not infiltrate May infiltrate surrounding breast
Stromal overgrowth defined as at least one low power field (40x total magnification) composed entirely of stroma

 

Adenomatous Transformation of Fibroadenoma Tubular Adenoma
Areas of typical fibroadenoma stroma Scant stroma
Variable tubules Uniform tubules
Areas typical of tubular adenoma may be found within fibroadenomas

 

Fibroadenoma Fibrocystic Disease
Discrete, circumscribed lesion May contain poorly circumscribed areas of fibrocystic change

 

Fibroadenoma Mammary Hamartoma
Lobules infrequent Lobules typically present (may be atrophic)
Frequent intracanalicular or tubular glandular proliferation Morphologically normal ducts and lobules
Intralesional fat rare Fat integral to lesion

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