Interrelation between western type cancers and non-western type cancers as regards their risk variations in time and space. III. A contrast between bladder cancer and stomach cancer.

The present study attempted to get insight into the etiology of bladder cancer by investigating the relation of this neoplasia to other 4 cancers as regards their risk variations in time and space. The results obtained are as follows: 1) Caucasians in Western countries were more inclined to develop bladder cancer than other ethnic groups, as compared among 43 population units of the world in terms of the age-adjusted incidence rate (AAIR). 2) In the same 43 comparison sets, male populations were always higher than female populations in their bladder cancer risks. The male to female ratio for the majority of the populations ranged from 3 to 4. In some population units, the ratios were much higher. In both male and female populations, the cancer risk increased with age. 3) Bladder cancer incidence in the world has been rising during the past 20 years, as detected in the follow-up study of 16 population units. 4) A negative linear relationship was detected for both sexes between bladder cancer and stomach cancer (non-Western type) regarding their log-transformed AAIRs, as calculated with data of the same 16 population units from 1960 through 1980. The same calculation with the esophagus cancer-bladder cancer pair gave marginally negative and no correlations respectively in the male and female populations. A positive linear relationship was detected in the comparison of bladder cancer with 2 Western type cancers (cancers of the colon and lung). 5) Japanese immigrants to the US were just in between Whites in the US (high-risk populations) and native Japanese (low-risk populations) in their bladder cancer risks. The same Japanese immigrants were again just in between Whites in the US (low-risk populations) and native Japanese (high-risk populations) in their stomach cancer risks. In conclusion, bladder cancer is a Western type cancer with sex and age discriminations in its occurrence. The cancer risk also varies depending on the life style of a population (environment dependent). The results obtained are discussed from the point of view of endocrinological oncology.