Carcinoma ex spiradenoma/cylindroma confirmed by immunohistochemical and molecular loss-of-heterozygosity profiling.

We present a case of spiradenoma/cylindroma with admixed carcinoma of unknown origin, resolved using immunohistochemical and molecular loss-of-heterozygosity (LOH) profiling. The patient, a woman in her mid-70s, initially presented with separate mammary (ductal) carcinomas of the right and left breasts that were treated with radical mastectomies. For 9 years, the patient remained disease free until complaining of a slow-growing skin nodule on the lower back that was excised under clinical suspicion of metastatic mammary carcinoma. Histopathological exam revealed a benign eccrine spiradenoma/cylindroma and an intermixed carcinoma, with a differential diagnosis of either primary eccrine carcinoma or mammary carcinoma metastatic to the spiradenoma/cylindroma. Histological features and immunohistochemical staining favored eccrine carcinoma but not unequivocally; therefore, LOH profiles were performed on archival paraffin block tissue from the 3 neoplastic lesions (4 components). The mammary carcinomas showed disparate LOH at 5 of 7 (right breast) and 4 of 7 (left breast) informative genetic loci, establishing these carcinomas as separate primary neoplasms. Both the spiradenoma/cylindroma and eccrine carcinoma revealed no LOH at the tested loci, establishing the unknown carcinoma as an independent carcinoma arising within a spiradenoma/cylindroma. This neoplasm is referred to in the literature as carcinoma ex spiradenoma/cylindroma and spiradenocylindrocarcinoma.