Distant metastasis form morphologically low-grade spiradenocarcinoma: a report of two cases.

Malignant tumors arising from benign eccrine spiradenomas are rare. They are divided by morphology into low-grade and high-grade spiradenocarcinomas, with prognosis and metastatic potential closely linked to their histopathologic features. Tumors with low-grade morphology are known for their indolent behaviour, with only two reported instances of metastatic spread. We report herein two further low-grade metastatic spiradenocarcinoma resulting in distant metastasis. Both tumors showed a background of a benign spiradenoma and subtle histopathologic signs of malignant transformation, characterized by loss of the dual cell population, up to moderate cytological atypia and increased mitotic activity. Both patients developed metastases to the lungs years after the initial presentation, and one showed additional lymph nodal disease. We demonstrate that even the morphologically low-grade tumors may rarely demonstrate more aggressive behavior. Although often challenging, recognition of the morphologically low-grade malignant spiradenocarcinoma and long-term follow-up of the patients are important to detect metastatic disease.