Findings from large study show a trend, but reasons aren't clear
MONDAY, Jan. 7 (HealthDay News) -- Men who father children may be at higher risk of prostate cancer compared to those who forego the life experience, a Danish study suggests.
The large-scale study looked at all men born in Denmark between 1935 and 1988. It found that childless men had a 17 percent lower incidence of prostate cancer than fathers did.
The reasons why remain unclear.
"It is not possible from the current data to point out what factors associated with childlessness, whether biologic, environmental, social or behavioral, were responsible for the observed reduction in prostate cancer risk," wrote researchers at the Statens Serum Institut, in Copenhagen.
The study is published in the Jan. 7 online edition of Cancer, and will appear in the journal's Feb. 15 print edition.
The findings echo those of a prior Scandinavian study, published in 2005, which looked at more than 48,800 cases of prostate cancer. That report also found a 17 percent lower incidence of prostate cancer among childless men.
In neither of the two studies did the gender of the children fathered affect the man's risk of prostate cancer. However, one large-scale study conducted several years ago in Israel found that the malignancy was 40 percent more common among men with no sons.
Dr. Susan Harlap, now a professor of epidemiology at New York University, led that Israeli study. She said the differing results reflect the complex factors, genetic and otherwise, that underlie prostate cancer risk throughout the world.
"The incidence of prostate cancer is different in Israeli Jews than in northwestern Europeans," Harlap said. "It may be a different disease, and there may be a different set of causes. We do know there are genetic causes of prostate cancer, and there could be different sets of genes in Israeli Jews than in northwestern Europeans."
A relationship between prostate cancer risk and having no sons would point to a mutation in the Y chromosome, which determines the male sex of a child. But there are complexities to such a relationship, Harlap noted.
"If the effect is due to Y chromosomes, they are quite specific to ethnic groups," she said. "Israeli Jews are different from Danes and Swedes."
The complexity of the issue is also illustrated by the different findings of the two Scandinavian studies about fatherhood and risk. The new Danish report finds that "among fathers, a significant trend was observed of gradually reduced prostate cancer with increasing number of children" -- in other words, fatherhood was linked to an increased risk for prostate cancer, but fathering more children begins to bring that risk down again. In contrast, the earlier study found "no further change in risk associated with fathering of more than two children."
Dr. Otis Brawley, chief medical officer of the American Cancer Society, was less than impressed by the Copenhagen findings, however. Despite the large numbers, the result was "just barely statistically significant," Brawley said, and could be the result of pure chance.
In a study of this kind, he said, "you occasionally get something that is statistically significant but is not really significant biologically."
In any case, men shouldn't make decisions on fatherhood based on the study results, Brawley stressed. "I would never suggest to men that their wives not get pregnant so they don't get prostate cancer," he said. "Lack of fatherhood is not a strong preventive of prostate cancer."
Any relationship that does exist is probably very weak, Brawley said. "If there is a real correlation, I would like to know what the true cause is," he said. "I suspect we will never know."
There's more on prostate cancer at the American Cancer Society.
SOURCES: Susan Harlap, M.D., professor, epidemiology, New York University, New York City; Otis Brawley, M.D., chief medical officer, American Cancer Society, Atlanta; Jan. 7, 2007, Cancer online
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