Forty-year-old woman with gradual growth of right breast mass initially diagnosed as tubular adenoma (TA) at age 34, 6 months into a pregnancy. Multiple family members on her maternal side were diagnosed with breast and ovarian cancer at unknown ages, with several found to have a pathogenic BRCA mutation. A: Current right craniocaudal (left) and mediolateral oblique (right) tomosynthesis images show an oval, equal density mass (arrows) at the 8 o'clock position with a biopsy clip along its posterior aspect. B: Current transverse (left), longitudinal (center), and Doppler (right) US images show an avascular, oval, parallel, hypoechoic mass with microlobulated margins (arrows), which had increased from 10 × 4 × 7 mm 6 years ago (not shown) to 21 × 9 × 20 mm currently. Because of the increase in size and high-risk family history, this mass was assessed as BI-RADS 4A and the patient underwent surgical excision. C: Histopathology (4×, hematoxylin and eosin, 10× close-up on right) from initial US-guided 14-g core-needle biopsy, taken when the patient was age 34, shows bland tubular proliferation (arrows) and relatively sparse stroma, consistent with TA. D: Histopathology (4×, hematoxylin and eosin, 10× close-up on right) of the surgical specimen at age 40 now shows abundant stroma surrounding and distorting ducts (curved arrows) and acini (arrows), typical of a fibroadenoma (FA). This case appears to show evolution over time from TA to FA. Some possible explanations include “maturation” of a TA to FA, initial biopsy sampling of adjacent normal lactational breast tissue during pregnancy and mischaracterizing the sample as TA, or resolution of lactational changes in a FA over time.