Acetylcholine receptor expression in Merkel cell carcinoma.

Neurocrest-derived tissues express muscarinic and nicotinic acetylcholine receptors (mAChR and nAChR respectively). These receptors are critical for migration of neurocrest-derived cells to their corresponding tissues during development. Recent reports demonstrate neurocrest-derived melanoma and numerous non-Merkel cell neuroendocrine tumors express both muscarinic and nicotinic receptors. In light of the controversy surrounding the origin and pathogenesis of Merkel cell carcinoma (MCC), we investigated the immunohistochemical expression of both mAChR and nAChR in MCC. Fifteen cases of primary non-metastatic cutaneous MCC archived at a large veterans' hospital and tertiary referral dermatopathology service were retrieved by computer-assisted search. Immunohistochemistry was utilized to evaluate the presence of M3, M5 and beta 2 nAChR expression. All the cases were confirmed prior to study by a single board certified dermatopathologist (MBM). Fifteen cases of primary cutaneous MCC were diffusely positive for M3 and M5 mAChR staining. All cases lacked immunohistochemical staining for the beta 2 nAChR. Despite the limited number of cases, MCC appears to uniformly express M3 and M5 receptors. These receptors have been linked to cell proliferation and migration which may confer a potential therapeutic target.