Neuroendocrine skin carcinoma associated with calcitonin production: a Merkel cell carcinoma?

An elderly woman presented with an ulcerating skin carcinoma located over the right parietal area. It healed after local radiotherapy but recurred locally and metastasized to the subcutaneous tissue and one regional lymph node. Neurosecretory granules were demonstrated ultrastructurally, and blood levels of calcitonin were repeatedly elevated. A metastasizing medullary carcinoma of the thyroid was suspected, and a total thyroidectomy was performed; however, no medullary carcinoma or C cell hyperplasia could be identified. Furthermore, the calcitonin levels remained unchanged following thyroidectomy, whereas they decreased twice after the skin tumor or its metastases were ablated. Clinical follow-up for over seven years revealed no other lesion that could have been responsible for the overproduction of calcitonin. The ultrastructural features of this skin carcinoma and its metastases, particularly the neurosecretory granules, were reminiscent of those of the so-called Merkel cell. We conclude that this skin carcinoma might indeed produce calcitonin, that this tumor may be derived from Merkel cells, and that Merkel cells may belong within the APUD system.