Risk of Fibroadenoma Converting to Malignancy

Clinical Classification and Risk Stratification

The National Comprehensive Cancer Network guidelines classify stable fibroadenomas unchanged on successive ultrasound studies as BI-RADS Category 2 (Benign Finding), essentially negative for malignancy, with a classification based on imaging characteristics and associated cancer risk 1, 2
Fibroadenomas with circumscribed margins, oval shape, and horizontal orientation have less than 2% risk for malignancy and are classified as BI-RADS Category 3 (Probably Benign) 1, 2

Phyllodes tumors often appear identical to fibroadenomas on ultrasound and mammography, making preoperative distinction difficult 3
In the setting of a large (>2 cm) or rapidly enlarging clinical "fibroadenoma," excisional biopsy should be performed to pathologically exclude phyllodes tumor 3

The American College of Radiology recommends excision for fibroadenomas larger than 2 cm in size and for patient request or anxiety about the mass 4