Overall, approximately 63 percent of HCC was associated with one or more risk factors mentioned above ” a relationship that was highest among Asians (67.9 percent) and lowest among blacks (53.5 percent).

Diabetes was associated with the greatest percentage of cases (33.5 percent), followed by alcohol-related disorders (23.9 percent), HCV infection (20.7 percent), HBV infection (5.7 percent), rare metabolic disorders (3.1 percent) and obesity (2.7 percent), according to McGlynn.

These risk-factor-related percentages varied individually by racial/ethnic group and gender.

"This research suggests that it would be worthwhile to target HCC prevention strategies at persons with diabetes, in addition to persons with other risk factors such as alcohol-related conditions, HCV and HBV infection," McGlynn said.

The researchers are currently expanding on these results by conducting follow-up studies to determine whether the risk of HCC among people with diabetes is affected by their diabetes medications. Ultimately, however, McGlynn and colleagues hope to determine the unidentified risk factors linked to the 37 percent of HCC cases not explainable by the risk factors above.

4699. Environmental tobacco smoke in relation to bladder cancer risk: The Shanghai Bladder Cancer Study

Exposure to environmental tobacco smoke, also called secondhand smoke, increased the risk of bladder cancer among participants of a population-based study conducted in Shanghai, China.

Specifically, lifelong nonsmokers whose mothers smoked more than 10 pack-years had a 3.51-fold increased risk of bladder cancer compared to lifelong nonsmokers who had never been exposed to secondhand smoke. A pack-year is defined as 20 cigarettes smoked every day for one year.

A similar, albeit weak association with bladder cancer risk was observed for those who were exposed to secondhand smoke from other family members living in the same household. People working in an office shared with coworkers who smoked cigarettes five or more hours a day also were at two-fold increased risk of bladder cancer.

"This is the first time there has been a clear demonstration of the effect of secondhand smoke on bladder cancer risk," said Li Tao, M.D., lead author and a research fellow at the Masonic Cancer Center, University of Minnesota.

Previous studies, mostly epidemiological ones, failed to establish a strong association due to inadequate measures of secondhand tobacco exposure and small number of subjects involved. By contrast, Tao's study included more than 200 bladder cancer patients and an equal number of healthy participants who never used tobacco products.

In-person interviews were conducted using a structured questionnaire to ask participants for the smoking history of their mothers, fathers and other family members during subjects' childhood at home. Besides domestic settings where spouses and other family members smoked cigarettes, the questionnaire asked participants about the smoking habits of coworkers at their workplace. This thorough and comprehensive ascertainment for exposure to secondhand smoke made this study unique and stood out from previous studies.

Furthermore, some genetically determined enzymes such as cytochrome P450 1A2 (CYP1A2) and N-acetyltransferase 2 (NAT2), which catalyze the metabolism of potential bladder carcinogens present in tobacco smoke, were measured on all participants. These laboratory measurements provided further clues to the link of the secondhand smoke to bladder cancer.

Overall, those who were exposed to secondhand smoke had a 20 percent to 30 percent increased risk of bladder cancer, but this was what statisticians call a non-significant finding, suggesting it could have resulted by chance. However, when researchers considered only participants who had an elevated CYP1A2 enzyme activity (which activates more tobacco bladder carcinogens) and a low NAT2 enzyme activity (which slows the detoxification of tobacco bladder carcinogens), secondhand smoke was associated with more than two-fold increased risk of bladder cancer, which was statistically significant.

These findings suggest that the genetic traits may contribute to the overall risk of bladder cancer for a given individual who is exposed to secondhand smoke.

"Given the complexity in genetically determined metabolism of tobacco bladder carcinogens, this genetic analysis will need to be further explored," Tao said.

SOURCE American Association for Cancer Research