A 28 year old woman presents with a painless lump in her left breast. This was first discovered 5 years ago and diagnosed to be a fibroadenoma. Subsequently, she opted for observation alone. However, the lump rapidly increased in size over the past 1 year, prompting her to seek medical attention. No other symptoms were present. Her medical history is otherwise unremarkable and she is not on any medications, including oral contraceptives. There is no family history of breast, ovarian, or gastrointestinal malignancies. She has two children, both of whom were breastfed, for a total of 2 years. Her menarche was at 12 years of age, and her menstrual cycles are regular. She does not smoke, and only drinks socially.
There is a 4.2 x 4.3 cm lesion in the left breast, which is round in shape, well circumscribed, and homogeneously hypoechoic. The left axilla appears normal. The right breast and axilla also appear normal.
There is a 4.2 x 4.3 cm lesion in the left breast, which is round and well circumscribed. The lesion is isodense on T1-weighted images, and heterogeneously hyperintense on T2-weighted images. The right breast appears normal.
CA 15-3, CA-125, CA 19-9, alpha-fetoprotein (AFP) and carcinoembryonic antigen (CEA) levels are all normal.
Microscopy of the biopsy sample reveals a fibroepithelial proliferative lesion. The epithelial component is benign in appearance and shows a leaf like 'intra-canalicular' pattern. The stromal element is unevenly hypercellular, with moderate atypia and stromal overgrowth; there are 6 to 7 mitotic figures per 10/high powered fields (HPFs). The overall appearance is that of a borderline phyllodes tumor.