Men who father daughters, not sons, are more likely to develop prostate cancer, according to a new study released on Wednesday.
The researchers found men with three daughters and no sons were up to 60 per cent more likely to develop prostate cancer.
Prostate cancer is the most common male cancer. It affects the prostate, a gland the size of a walnut under the bladder that makes fluid for semen.
Researchers at Columbia University's Mailman School of Public Health in conjunction with Jerusalem's Hebrew University looked at more than 38,000 men and compared the families of the more than 700 diagnosed with prostate cancer with those of the other men.
The findings, published in the most recent issue of the Journal of the National Cancer Institute, show the relative risk of prostate cancer drops as the number of sons increases.
"We surveyed vital status and cancer incidence, and found a strong trend for a decrease in prostate cancer risk as the number of sons increased," said Dr. Susan Harlap, professor of clinical epidemiology at the Mailman School of Public Health, and the leader of the research team.
"We anticipate that this finding will have a significant impact on the direction of research in this field going forward," Harlap, who led the research team, said in a written statement.
Overall, men with only daughters were 40 per cent more likely to develop prostate cancer. The risk increased when a man had three or more daughters and no sons.
The researchers suggested the risk of prostate cancer increased because of health screening. It was also possible that a predominantly female family may encourage a man to be more health-conscious, they said.
The researchers also suggested men with several daughters may seek medical attention to find out why they hadn't fathered a son.
However, many experts discount those theories and say the increased risk is linked to genetics.
The study suggests the cause of an increased risk may be the male "Y" sex chromosome, which could not only affect the likelihood of having boys but lead to cancer development.
The offspring's sex depends on whether it receives an X or a Y chromosome from the father. A man with a damaged Y chromosome will be less likely to have sons.
"Our findings suggest that the biological significance of lack of sons -- whatever it is that leads to increased risk of prostate cancer -- becomes increasingly important as family size increases," Harlap said.
"Overall, our findings are consistent with hypotheses that tie Y chromosome loci to prostate cancer, although other explanations cannot be excluded," she added.
In addition to Columbia University's Mailman School of Public Health and Department of Psychiatry, the international team of scientists included researchers from Jerusalem's Hebrew University-Hadassah School of Public Health and the Braun School of Public Health.
The Canadian Cancer Society estimates that 20,700 men in this country will be diagnosed with prostate cancer this year and 4,200 will die from the disease.
