Merkel cell carcinoma: a review of clinical management with focus on Asian patients.

Merkel cell carcinoma is a highly aggressive skin cancer characterized by neuroendocrine differentiation. This review aimed to present updates on the knowledge and current trends of clinical management of Merkel cell carcinoma. Additionally, we focused on Asian reports of Merkel cell carcinoma because most skin cancers differ substantially between Caucasians and Asians, and researchers have reported differences in Merkel cell carcinoma in racial and ethnic groups. Owing to its rarity, there is limited evidence for the epidemiology, pathogenesis, diagnosis and Merkel cell carcinoma treatment. The development of a nationwide survey or cancer registry, the identification of Merkel cell polyomavirus and the use of immune checkpoint inhibitors allowed a better understanding of its characteristics and biology and have revolutionized the clinical management of patients with Merkel cell carcinoma. Its incidence has gradually increased worldwide; however, it depends on the geographic location, race and ethnicity. No randomized prospective studies have evaluated the significance of sentinel lymph node biopsy, complete lymph node dissection and adjuvant radiation therapy; however, most patients with localized Merkel cell carcinoma are treated surgically or with post-operative radiation. Patients with distant Merkel cell carcinoma are administered immune checkpoint inhibitors as the first-line therapy; however, there is no established second-line therapy for refractory Merkel cell carcinoma. Furthermore, it is necessary to validate the favorable results of clinical studies performed in Western countries in the patients in Asia.