Pregnancy and risk of renal cell cancer: a population-based study in Sweden

Epidemiological findings indicate that hormonal influences may play a role in the etiology of renal cell cancer (RCC). The possible effect of childbearing remains enigmatic; while some investigators have reported a positive association between number of births and renal cell cancer risk, others have not. A case-control study, nested within a nation-wide Fertility Register covering Swedish women born 1925 and later, was undertaken to explore possible associations between parity and age at first birth and the risk of renal cell cancer. Among these women a total of 1465 cases of RCC were identified in the Swedish Cancer Register between 1958 and 1992 and information on the number of live childbirths and age at each birth was obtained by linkage to the Fertility Database. For each case, five age-matched controls were randomly selected from the same register. Compared to nulliparous women, ever-parous women were at a 40% increased risk of RCC (Odds Ratio [OR]=1.42; 95% CI 1.19-1.69). The corresponding OR for women of high parity (five or more live births) was 1.91 (95% CI 1.40-2.62). After controlling for age at first birth among parous women, each additional birth was associated with a 15% increase in risk (OR=1.15; 95% CI 1.08-1.22). The observed positive association between parity and renal cell cancer risk is unlikely to be fully explained by uncontrolled confounding, but warrants further evaluation in large studies, with allowance for body mass index.