Men who father daughters, not sons, may be at a greater risk of developing prostate cancer, researchers have said.
The gender of a man's children may be linked to his cancer risk
The Israeli team found men with three daughters and no sons were up to 60% more likely to develop prostate cancer.
But the Journal of the National Cancer Institute study suggests the cause may be the male "Y" sex chromosome, not the act of having either a son or daughter.
UK experts said a common genetic cause may affect both cancer risk and the chance a man will father girls.
Prostate cancer is the most common male cancer, with more than 30,000 new cases in the UK in 2003.
It affects the prostate gland, which is found near the bladder in men, and produces one component of semen.
The Israeli research looked at more than 38,000 men, and compared the families of the 712 diagnosed with prostate cancer with those of the other men.
Overall, compared with men who had at least one son, those with only daughters were 40% more likely to develop prostate cancer.
The risk increased when a man had three or more daughters and no sons.
The researchers looked for alternative explanations for the apparent difference.
Since prostate problems are often only detected when a man attends for routine health screening, they suggested that it was possible that having a predominantly female family might encourage a man to be more health-conscious.
Another possibility was that men having daughter after daughter might go to the doctor to find out if there was any problem stopping them from fathering a son.
However, there was no evidence to support these explanations, and the researchers suggested that a genetic cause could be contributing to both the birth of daughters and the risk of cancer.
Men supply one sex chromosome in their sperm - this can be either a Y, producing a male embryo, or an X, producing a female embryo.
Faults on the man's Y chromosome might not only affect the likelihood of conception or development of male offspring, but also lead to cancer development, it was suggested.
The Prostate Cancer Charity head of policy and research Chris Hiley said: "This is an interesting study - it certainly attracts the attention, but it doesn't yet translate into useful advice for men until other complex genetic studies are done.
"Further research to confirm these findings in men from other parts of the world is needed.
"We also need to uncover exactly what it is about the Y chromosome, which only men have, that might make men who are diagnosed with prostate cancer also more likely to have fathered girls rather than boys.
"In the meantime no-one should rush off with the idea that girls give their fathers prostate cancer."