Fibrous Disease of the Breast Can Obscure Breast Cancer Margins on Ultrasound: A Case Report

No studies have reported the occurrence of breast cancer within the fibrous disease of the breast to date. An 87-year-old nulliparous woman with a prior history of colon cancer surgery had been diagnosed with core needle biopsy-proven fibrous disease of the breast one year before. Follow-up mammography showed no change in the focal asymmetric density to which fibrous disease of the breast corresponded. Ultrasound also showed no marked changes in ill-defined low echoic areas, but clarified the disruption of the anterior margins of the mammary gland and more enhanced posterior echoes than before. Magnetic resonance imaging (MRI) of the target areas showed low signals on T1-weighted images, focal high signals in the large areas of low signals on fat-suppressed T2-weighted images, focal high signals on diffusion-weighted images, and focal both early and retained enhancement on dynamic studies, highly suggesting possible malignancy. Repeat core needle biopsy of the possible malignancy areas showed atypical cells with fibrous components, inflammatory cell infiltration, and vasculitis-like findings, leading to the diagnosis of breast cancer in the fibrous disease of the breast. Immunostaining showed estrogen and progesterone receptor negativity, human epidermal growth factor receptor type 2 positivity, and a high Ki-67 labeling index of 80%. The patient's preference and her old age made us treat the patient not with neoadjuvant chemotherapy but with primary breast-conserving surgery and sentinel node biopsy. Pathological study showed no metastasis in the sentinel node and invasive breast cancer measuring 19 mm in the fibrous disease of the breast. The patient recovered uneventfully, was discharged on the second day after surgery, received one year of trastuzumab monotherapy as the postoperative adjuvant therapy due to the patient's strong preference, and has been well for 14 months. Diagnostic physicians should note that unilateral fibrous disease of the breast should be evaluated with MRI before tissue sampling, and the change of posterior echoes is an important diagnostic clue for the diagnosis of breast cancer in the fibrous disease of the breast.