Spiradenocarcinoma arising in preexisting benign spiradenoma: molecular findings of a rare entity

Summary: Background: Spiradenocarcinomas are rare and aggressive skin adnexal neoplasms arising from a benign spiradenoma of the eccrine sweat gland. To date, little is known about the underlying molecular background of these malignant tumors. Here, we report a rare case of spiradenocarcinoma ex spiradenoma. Case presentation: A 69-year-old male presented with a 4.0 cm mass in the left upper extremity, which has been present for several months and recently progressively enlarged. A local excision was performed. Microscopic examination demonstrated areas of high-grade spiradenocarcinoma with infiltrative border and extensive necrosis, while the remaining parts of the tumor show benign precursor spiradenoma. Next-generation sequencing showed the ALPK1 p.V1092A mutation in both spiradenoma and spiradenocarcinoma components. Additional mutations and gene deletions were found in the spiradenocarcinoma component involving the BAP1, PIK3R1, SMARCA4, TP53, and CDKN2A/B genes. Conclusion: This case highlights the transition of a benign spiradenoma into a high-grade spiradenocarcinoma. Molecular analysis confirmed that ALPK1 mutation is the driver mutation of both spiradenoma and spiradenocarcinoma.