Distant Metastasis of Merkel Cell Carcinoma: A Descriptive Study

There are few studies on the pattern of distant spread of Merkel cell carcinoma (MCC). To analyse the most frequent locations of distant metastases from MCC and their possible relationship with the location of the primary tumour. Patients diagnosed with cutaneous MCC between 1988 and 2022 were included in the study. The locations of the first metastases detected were recorded, both at tumour diagnosis and during follow-up after initial treatment. One hundred patients were diagnosed with MCC. Distant metastases were detected in 31 patients (seven at diagnosis and 24 during follow-up), with a total of 52 locations: 17 non-regional lymph node metastases, 10 bone, seven liver, six lung, four non-regional cutaneous/subcutaneous, three pancreatic, two adrenal, two pharyngeal, and one mammary. No patient developed metastasis to the central nervous system. Recurrences occurred in 84% of patients before two years of follow-up. Although differences were not significant, MCCs located in the extremities tended to metastasize to extra-regional lymph nodes and those in the head and neck to bone, liver, and lung. MCC produces metastases mainly in non-regional lymph nodes, bone, liver, and lung. Given its high frequency (1/3 of patients), we consider performing scheduled imaging tests during the first two years of follow-up advisable. Specific imaging tests for central nervous system could be reserved for patients with neurological symptoms.