Circumscribed, often large, breast mass usually occuring in adolescent females with stromal and epithelial hypercellularity but lacking the leaf-like growth pattern of phyllodes tumors
Alternate/Historical Names
Benign cystosarcoma phyllodes
Cellular fibroadenoma
Cellular adenofibroma
Fetal fibroadenoma
Juvenile adenofibroma
Diagnostic Criteria
Circumscribed
Rarely multiple
Biphasic stromal and epithelial process
Pericanalicular pattern most common
May be mixed with intracanalicular
Lacks leaf-like growth pattern
Uniformly hypercellular stroma
Fibrotic areas may be present
Lacks atypical features
No periductal increase in cellularity
No stromal overgrowth
No cytologic atypia
Mitotic rate < 3/hpf
Frequent epithelial and myoepithelial hyperplasia
May mimic that seen in gynecomastia
May be atypical
Most patients age 10-20
(Most fibroadenomas in adolescents are typical, adult type fibroadenomas and should be diagnosed as such)
Giant fibroadenoma
Tumors >500 g or disproportionally large compared to rest of breast
More frequent in young and black patients
We consider the term merely descriptive
May be either adult type or juvenile fibroadenomas
