Spiradenocarcinoma With Associated Mucinous Glandular Differentiation: A Unique Histopathologic Presentation of a Rare Diagnosis.

Spiradenocarcinoma, also known as malignant eccrine spiradenoma or malignant spiradenoma, is a rare malignant adnexal tumor. We present a case of a 60-year-old woman with an enlarging, symptomatic, 5-cm exophytic mass on her left scalp, which was treated with wide local excision after a biopsy demonstrated suspicion for a ductal neoplasm. Histopathologic examination revealed a dermal tumor composed of nodules of monotonous basaloid cells with small intratumoral duct-like structures. In addition, squamous morules and scattered small glands with mucinous cytoplasm were seen. Immunohistochemical staining showed positivity for cytokeratin 7, p63, epithelial membrane antigen, SOX-10, and carcinoembryonic antigen (in duct lumens), with increased Ki67 proliferation index. A small focus reminiscent of benign spiradenoma was also noted. The final diagnosis was consistent with spiradenocarcinoma, uniquely presenting with mucinous glandular differentiation and squamous morules. This case highlights the importance of using precise histopathologic descriptors in diagnosing rare adnexal tumors and contributes to the growing body of literature on the heterogeneous morphology of these malignant lesions.