Background: Lateral distribution of cancer has been observed previously. Most evident is this laterality in ultraviolet (UV)-induced skin cancer, based on an unequally distributed UV exposure.
Objectives: The aim of this study was to explore whether patients from Germany also show asymmetrical lateral distribution of Merkel cell carcinoma (MCC).
Methods: In total, 115 patients with MCC were studied for laterality of the primary tumour. Correlation of clinical variables with lateral distribution of MCC was investigated as well.
Results: In 64/115 (55.7%) patients, primary tumours were present on the left side, in 37/115 (32.2%) on the right side, and in 14/115 (12.2%) in the midline (P < 0.0001). Excluding the latter localization occurrence of left-sided MCCs (64 of 101/63.4%) was significantly (P = 0.0072) more often observed (1.73-fold) when compared to right-sided tumours (37 of 101/36.6%). The excess of left-sided tumours was found on the head with a left-right ratio of 1.8, trunk of 8, arm of 1.2, and leg of 1.8. There was no significant association between laterality and gender, age, MCPyV status, and anatomic localization of primary tumours including the occurrence in sun-exposed sites.
Conclusions: Occurrence of left-sided MCCs was significantly more often observed when compared to right-sided tumours. Laterality was not associated with tumour presentation at chronically ultraviolet-exposed sites. Hence, the reason for laterality in MCC remains obscure, but likely goes beyond UV exposure.
Keywords: Lateral distribution; Laterality; Merkel cell carcinoma.