Spiradenocarcinoma with low-grade basal cell adenocarcinoma pattern: report of a case with varied morphology and wild type TP53.

We present a patient with a 2-cm spiradenocarcinoma of the left arm resembling low-grade salivary gland basal cell adenocarcinoma. In addition to showing attributes of conventional spiradenoma, the benign component showed prominent areas of cystic change with focal apocrine differentiation, glands with and without mucinous differentiation, clear cell change and focal adenoid cystic carcinoma-like areas. The malignant component was composed of nodules of basaloid cells arranged in sheets with variable tendency to luminal differentiation. The nuclear atypia was low-grade, and the mitotic index was high in the malignant component (to 8/10 high power fields). Immunohistochemically, there was diffuse but variable positivity for cytokeratin 7 in both the benign and malignant components. Epithelial membrane antigen was focally positive, highlighting cells with ductal (luminal) differentiation. Expression of p63 was observed in 50 and 80% of the cells in the benign and malignant components, respectively. Calponin was negative. The proliferative index (MIB-1/Ki-67) was <3% in the benign component and up to 10% in the malignant component. Although the malignant component displayed patchy areas with nuclear p53 immunoreactivity with variable intensity, no mutation in the TP53 gene was identified.