Distant Metastasis of Merkel Cell Carcinoma: A Descriptive Study.

Introduction: There are few studies on the pattern of distant spread of Merkel cell carcinoma (MCC).

Objectives: To analyse the most frequent locations of distant metastases from MCC and their possible relationship with the location of the primary tumour.

Methods: 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.

Results: 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.

Conclusions: 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.