FAMILIAL BLADDER CANCER IN THE NATIONAL SWEDISH FAMILY CANCER DATABASE

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Abstract
We analyzed the risk of bladder cancer in offspring according to parental and sibling cancer using the national Swedish Family Cancer Database. Cancer data were obtained from the Swedish Cancer Registry for 1958 to 1996, including 2,105 cases of bladder cancer in offspring. The standardized incidence ratio was used to measure cancer risk in offspring according to familial cancer status. The incidence ratio of bladder cancer increased in Sweden from 1958 to 1996 and it was 3 to 4-fold higher in males than in females. We identified 65 families in which the parents and offspring had bladder cancer with a familial risk of 1.35 (95% confidence interval [CI] 0.97 to 1.79) in sons and 2.29 (95% CI 1.46 to 3.29) in daughters. Discordant cancer sites associated with bladder cancer in the 2 generations were the kidney and thyroid with a standardized incidence ratio of 1.58 (95% CI 1.18 to 2.05) and 1.89 (95% CI 1.00 to 3.05), respectively. Sibling risk was higher compared with offspring risk with a standardized incidence ratio of 2.96 (95% CI 1.41 to 5.08) and in males there was a statistically significant ratio of sibling-to-offspring risk of 2.66 (95% CI 1.29 to 5.45). Patient age at onset modified the familial risk. The highest familial risk of 7.26 (95% CI 2.61 to 14.24) was observed in the brothers of bladder cancer probands diagnosed before age 45 years. The relatively high ratio of sibling-to-offspring risk as well as observed gender specific effects in bladder cancer may reflect an X linked susceptibility gene.