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NEW YORK -- Men who have at least one son have a 40% lower risk for developing prostate cancer than doting dads with only daughters. Why? The Y chromosome may hold the answer, speculated researchers here.
NEW YORK, Jan. 4 -- Fathers who have sons may possess some protection from prostate cancer.
Men who have at least one son have a 40% lower risk for developing prostate cancer than doting dads with only daughters, reported Susan Harlap, M.B., of Columbia University here and Hebrew University in Jerusalem, and colleagues.
And it appears that each additional boy gives Dad an extra edge against prostate cancer, with the risk of the disease declining as the total of sons rises, the investigators reported in the Jan. 3 issue of the Journal of the National Cancer Institute.
The finding points to the possible involvement of prostate cancer genes lurking on the Y chromosome, the authors hypothesized.
"Some studies have suggested he involvement of loci on sex chromosomes, both X and Y," they wrote. "Because mutations or variants in sex chromosomes might alter the probabilities of having sons or daughters, we questioned whether the risk of this malignancy could be related to sex of offspring."
The investigators surveyed vital status and cancer occurrence in 38,934 fathers from the Jerusalem Perinatal Study, a family-based research cohort. The men, who became fathers from 1964 through 1976, were followed until 2005.
The investigators created Cox proportional hazard models to examine the relative risk of prostate cancer in relation to the sex ratio of the 92,408 children born to the wives/partners of men in the cohort. The data were controlled for changes in occurrence over time, age, the father's year of birth, and social and ethnic variables.
The authors found that 712 men were diagnosed with prostate cancer during the study period, and that the risk was higher among men with only daughters compared with men who had at least one son. The adjusted relative risk for fathers of girls only was 1.40 (95% confidence interval, 1.20 to 1.64, P<0.0001).
The risk also appeared to increase with the size of boy-free families. Men who had only one child, a daughter, had a relative risk of 1.25 (95% CI, 1.00 to 1.56). Men with two girls only had a relative risk of 1.41 (95% CI, 1.04 to 1.91), and those with three daughters and no sons had a risk of 1.60 (95% CI, 1.05 to 2.43).
"Men with no daughters showed no statistically significantly altered risk, compared with men who had offspring of both sexes. The relative risk of prostate cancer decreased as the number of sons increased (P trend <0.0001) but did not change with the number of daughters," the authors wrote.
Limitations to the study included a lack of information about offspring born to the men in the cohort outside of the study period, and a lack of information on family history of prostate cancer, individual screening behavior, or measure of prostate cancer progression, such as Gleason scores. In addition, the authors looked only at a single population, making it difficult to extrapolate the findings to other groups.
"The strongest evidence that our findings are unlikely to be spurious comes from data?which suggest that the biologic significance of lack of sons -- whatever it is that leads to increased risk of prostate cancer -- becomes increasingly important as family size increases," they wrote.