Stage-specific incidence trends of melanoma in an English region, 1996-2015: longitudinal analyses of population-based data

Abstract

The aim of this study was to examine temporal trends in overall and stage-specific incidence of melanoma. Using population-based data on patients diagnosed with melanoma in East Anglia, England, 1996-2015, we estimated age-standardized time trends in annual incidence rates for each stage at diagnosis. Negative binomial regression was used to model trends over time adjusted for sex, age group and deprivation, and to subsequently examine variation in stage-specific trends by sex and age group. The age-standardized incidence increased from 14 to 29 cases/100 000 persons (i.e. 4% annually). Increasing incidence was apparent across all stages but was steepest for stage I [adjusted annual increase: 5%, 95% confidence interval (CI): 5-6%, and more gradual for stage II-IV disease (stage II: 3%, 95% CI: 2-4%; stage III/IV: 2%, 95% CI: 1-3%)]. Stage II-IV increase was apparent in men across age groups and in women aged 50 years or older. Increases in incidence were steeper in those aged 70 years or older, and in men. The findings suggest that both a genuine increase in the incidence of consequential illness and a degree of overdiagnosis may be responsible for the observed increasing incidence trends in melanoma in our population during the study period. They also suggest the potentially lower effectiveness of public health awareness campaigns in men and older people.

Figure 1

Age-standardised incidence of melanoma (smoothed and observed) by stage at diagnosis, for a) women and b) men Smoothed rates are ‘lowess’ (locally weighted scatterplot smoothed) (i.e., the average of each observed yearly rate and rates in nearby years; in this case the bandwidth was set at 0.2). For 493 patients (5% of entire dataset) with missing values on stage, these values were imputed as described under ‘Multiple imputation’.

Figure 2

Estimated incidence rate ratios (IRRs) of a) Stage 1 and b) Stages II-IV melanoma for 2015 (vs. 1996), according to sex and age-group Displayed incidence rate ratios for stage-specific disease per year estimated from Model 2, to the power 19 (model form provided in Supplementary Box S1). For 493 patients with missing values on stage, these values were imputed as described under ‘Multiple imputation’.