Abstract
OBJECTIVE: To test the hypothesis that bladder cancer is a heterogeneous disease. PATIENTS AND METHODS: We examined the temporal trends of bladder cancer by histological subtype and by disease stage and grade using the National Cancer Institute's Surveillance, Epidemiology, and End Results data collected in 1973-2007. RESULTS: The age-adjusted incidence rates of bladder cancer showed a slight decrease from 1973 to 2007 (annual percentage change [APC] = -0.4, P < 0.05). Although the age-adjusted incidence rates of non-papillary transitional cell carcinoma decreased by about 53% from 7.9 per 100,000 in 1973 to 3.7 per 100,000 in 2007 (APC = -2.2, P < 0.05), the age-adjusted incidence rates of papillary transitional cell carcinoma increased by about 56% from 6.8 per 100,000 in 1973 to 10.6 per 100,000 in 2007 (APC = 0.5, P < 0.05). Among other rare histological subtypes, except for small cell carcinoma which showed a slightly rising trend, squamous cell carcinoma, adenocarcinoma and others all presented a decreasing trend. Similar patterns were found for different stages (localized, regional and distant), but a dramatic increasing trend of grade IV was found between 1998 and 2007 when a corresponding decreasing trend was shown for grades I, II and III. CONCLUSION: The results support the hypothesis that bladder cancer is a heterogeneous disease and taking disease heterogeneity into consideration in future epidemiological studies is essential.