Complete spontaneous regression of Merkel cell carcinoma: a review of the 10 reported cases.

Background: Merkel cell (neuroendocrine) carcinoma (MCC) is a very aggressive primary cutaneous neoplasm occurring most often on the head and neck of the elderly. Complete spontaneous regression (CSR) of MCC was first described in 1986. Since then other cases have been reported bringing the total to 10.
Objective: To review these 10 cases and obtain long-term follow-up data, to compare them for similarities and differences.
Method: Each original case report was extensively reviewed and authors contacted in most cases for confirmation and updated information.
Results: In no case did MCC recur after CSR was noted, although follow-up information in some cases was short. When CSR occurred, it was swift and dramatic with complete regression of skin and lymph node metastasis in 1-3 months.
Conclusion: While only 10 cases of CSR is a small number, MCC is itself a rare malignancy with just over 600 reported cases. Today most cases of MCC receive aggressive combined therapy effectively precluding diagnosis of CSR. The nature of regression in these 10 cases may point toward future immunologic therapy just as similar cases of CRS in patients with melanoma have led to advances in the immunologic treatment for that malignancy.