Malignant dermal cylindromas. Do they exist? A morphological and immunohistochemical study and review of the literature.

Malignant dermal cylindromas are very rare. We present a case of multiple cylindromas of the scalp with metastasis to a cervical lymph node. The morphology of the tumour was unusual in that it contained eccrine spiradenoma-like areas and foci of squamous differentiation with keratin formation. The immunohistochemical phenotype of the eccrine spiradenoma-like areas and the metastatic tumour was similar, but different from the areas of typical cylindroma. Although alleged "malignant" cylindromas have been reported, none have been described to have metastasized, whereas metastatic eccrine spiradenoma is well-documented. We reiterate that overlaps between dermal cylindroma and eccrine spiradenoma are more common than has been documented. In the rare event of metastases, it is the eccrine spiradenomatous component that is metastatic. We contend that there is no evidence that pure dermal cylindromas have metastasized.