Risk of second cancers after the diagnosis of Merkel cell carcinoma in Scandinavia.

BACKGROUND

Merkel cell carcinoma (MCC) is an aggressive neuroendocrine tumour of the skin that has been associated with a new tumour virus, the MCC polyomavirus.

METHODS

To investigate whether MCC may have a shared aetiology with other cancers, we investigated the risk of second cancers after the diagnosis of MCC using the national cancer registries in Denmark, Norway and Sweden.

RESULTS

The overall cancer incidence was increased among patients diagnosed with MCC compared with the general population in these countries (79 secondary cancers total, Standardized Incidence Ratio (SIR) 1.38 (95% confidence interval (CI): 1.10-1.72); 49 secondary cancer in females, SIR 1.7 (95% CI: 1.29-2.25); 30 secondary cancers in males and SIR 1.05 (95% CI: 0.73-1.5)). There were significantly increased incidence ratios for non-melanoma skin cancers (34 secondary cancers, SIR 8.35 (95% CI: 5.97-11.68)), melanoma of skin (6 secondary cancers, SIR 4.29 (95% CI: 1.93-9.56)) and laryngeal cancer (2 secondary cancers, SIR 9.51 (95% CI: 2.38-38)). The SIRs for these three cancer sites were also elevated on restricting the follow-up to cancers occurring at least one year after MCC diagnosis.

CONCLUSIONS

Patients diagnosed with MCC are at increased risk of a second cancer, particularly, other skin cancers. Conceivable explanations include the impact of increased surveillance of the skin and shared causative factors, for example, ultraviolet light exposure or MCC polyomavirus infection.