Is melanoma survival influenced by month of diagnosis?

Background: Despite being a well-documented phenomenon, seasonal variation in the incidence of cutaneous melanoma is poorly understood, and data on the seasonality of melanoma survival are scarce. We sought to explore the seasonal variation in melanoma incidence and survival in Belgium and to assess the characteristics and outcomes of cases diagnosed during the seasonal peak.

Methods: All cases of invasive cutaneous melanoma-patients over 15 years of age and registered by the Belgian Cancer Registry (BCR) from 2004 to 2009-were included (n=9782). Monthly variations in incidence were estimated by the ratio of the number of cases diagnosed each month to that diagnosed in January (Rmonth/January) using Nam's method. The observed and relative 5-year survival rates were adjusted on patient and tumour characteristics using Cox proportional hazards regression models and generalised linear models with a Poisson error structure, respectively.

Results: A peak in melanoma incidence was observed in June (RJune/January=1.64, 95% confidence interval (CI)=1.54-1.73). The 5-year observed survival (OS) and relative survival (RS) rates were significantly higher for patients diagnosed in June compared with other months (OSJune=84%, 95%CI=81-86 versus OSOthermonths=79%, 95%CI=78-80; RSJune=93%, 95%CI=90-95 versus RSothermonths=87%, 95%CI=86-88). After adjustment, the 5-year OS remained significantly higher for patients diagnosed in June (hazard ratioJune=0.78, 95%CI=0.62-0.98); however, the 5-year RS was no longer significantly different for patients diagnosed in June compared with other months (relative excess riskJune=1.16, 95%CI=0.73-1.84).

Conclusions: This study demonstrated a seasonal variation in melanoma incidence in Belgium with a peak in June for the period 2004-2009. When adjusted for patient and tumour characteristics, patients diagnosed in June had higher observed survival rates, but relative survival rates did not differ. Our findings do not support an influence of season of diagnosis on melanoma prognosis.