Retained Rim Enhancement in Mucinous Breast Cancer Suggests Aggressive Biology: A Case Report.

A 44-year-old premenopausal woman was referred to our hospital for a detailed examination of her left rapidly growing breast mass. Mammography only showed focal asymmetric density. Ultrasound showed a 14 mm oval mass with distinct borders, a high depth/width rate of 0.79, numerous punctate echogenic foci against background low echoes, and slightly enhanced posterior echoes. Magnetic resonance imaging (MRI) of the mass showed low signal intensity on T1-weighted images and high signal intensity with a slightly low signal intensity area in the mass center on fat-suppressed T2-weighted images. Subtraction MRI depicted early and retained rim enhancement patterns. The patient underwent a core needle biopsy of the breast mass. Pathological study showed that the tumor had atypical cells growing in a papillary fashion with abundant mucus, leading to the diagnosis of mucinous breast cancer. The patient, therefore, underwent breast-conserving surgery and sentinel node biopsy. A post-operative pathological study showed that the tumor had cancer cells mainly distributed in a ring fashion and extremely sparse cancer cells with thick fibrous septa in the mass center. Immunostaining showed that the mucinous breast cancer had estrogen and progesterone receptor positivities, human epidermal growth factor receptor type 2 equivocation, and a high Ki-labelling index of 50%. Diagnostic physicians should note that retained rim enhancement may predict the biological aggressiveness of mucinous breast cancers.