Abstract
The frequency of occurrence of mammary phyllodes tumors is about 0.3-1% or less of all mammary gland tumors, and the most frequent age of onset is in the 40s. Onset in the 10s is considered rare. We encountered a case of benign phyllodes tumor occurring in an 11-year-old girl, and report it here with a discussion of the literature. She was referred to our department with the chief complaint of a 3-cm right breast tumor showing indications of growth over the course of about two months. Needle biopsy led to a diagnosis of fibroadenoma, and imaging also yielded findings consistent with fibroadenoma, but in biopsy. Pathological results identified benign phyllodes tumor. Phyllodes tumors are often difficult to differentiate from fibroadenoma, and preoperative differentiation in the present case was challenging in light of the symptoms, images, and histological findings. Considering the possibilities of relapse or malignancy, it would be desirable for resection to include a margin of safety. However, particularly regarding benign tumors in young individuals, there is room for investigating whether to perform resection with an added margin or to perform re-excision. Careful determination of the treatment strategy is needed, including close follow-up.
