SHORT REPORT Season of diagnosis has no effect on survival from malignant melanoma Harindra Jayasekara 1,2 * , Emily Karahalios 2 , Vicky Thursfield 2 , Graham G. Giles 1,2 and Dallas R. English 1,2 1 Centre for Molecular, Environmental, Genetic and Analytic Epidemiology, Melbourne School of Population Health, The University of Melbourne, Carlton, Victoria, Australia 2 Cancer Epidemiology Centre, The Cancer Council Victoria, Carlton, Victoria, Australia Diagnosis in summer had been shown to be associated with better survival from some cancers, but such studies on malignant mela- noma where sun exposure is a risk factor for disease are rare. We evaluated seasonality in melanoma diagnosis and its effect on sur- vival in Victoria, Australia using 26,060 cases reported to the pop- ulation-based Victorian Cancer Registry during 1986–2004. To estimate the amplitude of the seasonal variation, we calculated the ratio of the number of melanoma cases diagnosed in summer to that in winter. Linear regression was undertaken to assess the var- iation in thickness, the main prognostic indicator for melanoma, by season of diagnosis adjusting for sex, anatomical site, year of diagnosis and age at diagnosis. We modeled excess mortality using Poisson regression controlling for possible confounders in order to study the effect of season of diagnosis on survival. An overall 46% summer diagnostic excess was evident (summer-to-winter ratio 1.46; 95% CI 1.41, 1.52). Results of linear regression showed that melanoma diagnosed in winter were thicker than those diagnosed in any other season (percentage difference in thickness 22.01, 26.97 and 210.68 for spring, summer and autumn, respectively; p < 0.001). In the Poisson regression model of relative survival, cases diagnosed in spring, summer or autumn had slightly lower excess mortality than those diagnosed in winter before adjustment for other variables, but after adjustment the excess mortality ratios were close to unity. Our findings do not support the hypoth- esis that melanoma cases diagnosed in winter have worse progno- sis than cases diagnosed in other seasons. ' 2009 UICC Key words: cancer; malignant melanoma; season; survival Malignant melanoma of the skin, with an estimated annual inci- dence of 132,000 cases globally, poses a significant public health problem in parts of the world predominantly inhabited by Cauca- sian populations. 1 The highest incidence rate worldwide is seen in Australia, where a large proportion of the population is of Euro- pean descent. 2 Seasonal variation in the diagnosis of melanoma with a summer peak and a winter trough is well documented. 3–11 Recent epidemi- ological studies indicate that people diagnosed with cancers of the breast, colon, prostate, lung and Hodgkin lymphoma during summer and autumn months have higher survival than people diagnosed during the winter. 12 In a study using cancer registry data from New South Wales, Australia, Boniol et al. 11 reported that melanoma cases diagnosed during the summer had higher sur- vival than those diagnosed during the winter, an association that persisted after adjustment for melanoma thickness, which also showed seasonal variation. In the present study, we analyzed data from the Victorian Can- cer Registry to investigate the seasonal variation in the diagnosis of melanoma and its effect on survival in Victoria, which is situ- ated in the temperate part of Australia, further away from the equator than New South Wales. Material and methods Study population The Victorian Cancer Registry has been population based since 1982, registering all malignant neoplasms including invasive ma- lignant melanoma of the skin (i.e. Clarke’s level II and greater) 13 notified by the hospitals and pathology laboratories in Victoria. Out of 27,473 cases diagnosed with invasive melanoma during the 19-year period 1986–2004, 1,413 with multiple primary melano- mas were excluded, and the remaining 26,060 analyzed for sea- sonal patterns in diagnosis and survival. Data from 1982 to 1985 were not included in the current analysis due to incomplete report- ing of melanoma thickness. Data on age, sex and melanoma site and thickness were extracted for individual cases. Statistical analysis To estimate the amplitude of the seasonal variation in diagno- ses, we calculated the ratio of the number of melanoma cases diag- nosed in summer to that in winter. 14 Separate analyses were car- ried out for cases diagnosed during four consecutive time periods (1986–1990, 1991–1995, 1996–2000 and 2001–2004), to compare potential differences in the seasonal pattern over time. We pooled data for three contiguous months to accumulate the incidence for each season, considering summer to be December–February; autumn: March–May; winter: June–August and spring: September–November. To assess the variation in thickness by season, linear regression was undertaken on the natural log of thickness adjusting for sea- son, sex, anatomical site, year of diagnosis and age at diagnosis. The assumptions underlying linear regression were investigated. Results of the linear regression are presented as percentage differ- ence in thickness for a unit increase in a continuous variable (age and year of diagnosis) or a percentage change in thickness com- paring one category to the designated reference category for cate- gorical variables (season, sex and anatomical site). To study the effect of season of diagnosis on survival, relative survival was computed using the period method. 15 Relative sur- vival is defined as the observed survival in the case group divided by the expected survival of a comparable group from the general population. 16 Expected survival was estimated using the Ederer II method from Victorian population life-tables stratified by age, sex and calendar time. 17 Poisson regression was used to model excess mortality, which allowed us to estimate the effect of age, sex, ana- tomical site, thickness and year of diagnosis while controlling for possible confounding effects. 18 The estimates from the model are interpreted as excess mortality ratios, i.e. an excess mortality ratio of two for males in comparison with females indicates that males experience 100% higher excess mortality than females following a diagnosis of melanoma. All statistical analyses were performed using the software pack- age Stata 10.0. 19 Results More than half the cases were male (Table I). The mean age at diagnosis was 56.5 years. For males, the most common site was *Correspondence to: Centre for Molecular, Environmental, Genetic and Analytic Epidemiology, Melbourne School of Population Health, The University of Melbourne, Level 1, 723 Swanston Street, Carlton, Victoria 3053, Australia. Fax: 161 3 93495815. E-mail: harindra_jaya@yahoo.com Received 7 December 2008; Accepted after revision 6 February 2009 DOI 10.1002/ijc.24368 Published online 18 February 2009 in Wiley InterScience (www.interscience. wiley.com). Int. J. Cancer: 125, 488–490 (2009) ' 2009 UICC Publication of the International Union Against Cancer