Editorial Comment from Dr Fukushima to Temporal trends in the incidence of distant‐stage bladder cancer among young individuals

Abstract

Bladder cancer is relatively rare in young populations, and several previous case–control studies have shown that younger patients with bladder cancer have more favorable clinical, pathological and prognostic features than their older counterparts. Furthermore, a recent molecular subtype analysis has shown that younger patients tend to have a urotheliallike A subtype, which is associated with clinically less aggressive disease according to the immunohistochemistrybased subtype classification by Lund University. This accumulated evidence suggests that older patients might be more substantially exposed to various drivers of carcinogenesis over their lifetime compared with younger patients. In the current study, Tully et al. reported bladder cancer incidence trends using the Surveillance, Epidemiology and End Results database, with a focus on young individuals. According to their results, the incidence of distant-stage bladder cancer modestly, but significantly, increased across the study period among individuals aged 40–49 years, and this trend was not observed in those aged 50–64 years and ≥65 years, reflecting that clinically aggressive disease might have been increasing among young populations in the USA. Although this phenomenon can be partly explained by improved diagnostic modalities for bladder cancer, it might also reflect increased exposure to risk factors for bladder cancer, including unknown environmental and occupational factors, among young individuals, as discussed by the authors. To date, various risk factors for bladder cancer have been reported: (i) lifestyle factors, such as smoking, obesity and dietary factors; and (ii) occupational factors, such as aromatic amines (e.g. benzidine and 2-naphthylamine) and other chemical substances by which bladder cancer can be induced, especially in workers in the dye, rubber and leather industries. It is of note that the number of overweight and obese individuals is currently increasing rapidly worldwide. Given that the current study reported by Tully et al. included bladder cancer cases between 1975 and 2015, the increased trends in the incidence of distantstage bladder cancer among young individuals appears to correspond with trends in overweight and obesity prevalence. Future studies based on epidemiological big data analyses might unveil possible contributors to the increased incidence of distant-stage bladder cancer among young individuals. Importantly, because the current study was carried out using the Surveillance, Epidemiology and End Results database, the findings need to be fully validated in other cohorts composed of populations from various countries and ethnicities. Nevertheless, the current study is epidemiologically and clinically relevant in that it suggests the possibility of the presence of contemporary risk factors for bladder cancer.