Spindle Cell Carcinoma Arising in a Mammary Hamartoma

Abstract

Spindle cell carcinoma is an extremely rare histological breast tumor type, accounting for 0.1-0.2% of all breast cancers. Its prognosis has been said to be poor, except for a sub-type of fibromatosis-like metaplastic carcinoma.

Mammary hamartoma is also a rare breast tumor known as “breast in breast”, accounting for 5% or less of all benign breast tumors. Although coexistence of malignancy with a hamartoma is uncommon, 24 cases of breast cancer arising in mammary hamartomas have been reported. Most of their histological types were ductal or lobular carcinoma, 17 invasive, 5 non-invasive, and one mixed, except for one mucinous carcinoma. This report presents the 25th case of breast cancer arising in a mammary hamartoma, and the first case whose histological type was spindle cell carcinoma.

An 85-year-old woman was referred to our hospital with a left breast tumor. On imaging, the tumor consisted of a double structure : the outer structure was well demarcated and homogeneous, high-echoic, adipose tissue density, 8.0 cm in diameter ; and the inner was irregular, low-echoic, soft tissue density, and 4.5 cm in diameter. She underwent partial mastectomy, and the pathological diagnosis was spindle cell carcinoma arising in a left mammary hamartoma, pT2NxM0 ; Stage IIA.