Adenoid squamous cell carcinoma of the skin overlying the right breast. An autopsy case clinically manifested with rapid growth and widely spreading metastases.

An autopsy case of a 62-year-old woman with a poorly differentiated, aggressive form of adenoid squamous cell carcinoma arising in the skin overlying the right breast was studied. The tumor, 9 X 8 cm in diameter, had rapidly enlarged since one year before admission from a verrucous lesion of 20 years duration. The histologic features of the tumor showed a well-differentiated squamous cell carcinoma mainly in the superficial areas, which transformed into, with a zone of transition in between, an alveolar or adenoid structure in the deep invading portion. The adenoid tumor cells exhibited an undifferentiated appearance with prominent nucleoli and frequent mitotic figures. These cells partly showed dyskeratotic or acantholytic features. Mucin was negative. The patient died at 8 months after the operation. Autopsy revealed widely spreading metastases in which an adenoid structure was outstanding. These unusual pathological features and an aggressive behavior of this tumor, which were hitherto rarely described for adenoid squamous cell carcinoma, seemed to be a poorly differentiated variant of the tumor. This malignant transformation might be derived from loss of cohesion of the pre-existing usual well-differentiated squamous cell carcinoma in the basal and parabasal layers, inparting marked invasiveness of these cells into the supporting connective tissue.