Women are more likely to develop breast cancer if their father or brother has suffered prostate cancer, a study has discovered.

Researchers in America noted that both illnesses are the result of a faulty gene passed through families and that it isn't just female family members who determine whether a woman will be affected in the future.

A study of 78,171 women over 16 years found females were 14 per cent more likely to be diagnosed with breast cancer if the male family members mentioned above had prostate cancer. Their chances increased if their mothers or sisters had breast cancer too, rising to 78 per cent.

It's already known that many health problems are inherited, but scientists believe these results prove that faulty genes are more important in determining future illnesses than previously thought.

The lead author of the study - which was published in the journal Cancer - urges doctors to ask ladies more questions during routine checkups, especially whether prostate cancer runs in her family, to ensure diagnosis can be made early and treatment started quicker.

Dr Jennifer Beebe-Dimmer of the Barbara Ann Karmanos Cancer Institute and Wayne State University School of Medicine in Detroit, who ran proceedings, explained the findings.

"The increase in breast cancer risk associated with having a positive family history of prostate cancer is modest; however, women with a family history of both breast and prostate cancer among first-degree relatives have an almost two-fold increase in risk of breast cancer," she said.

"These findings are important in that they can be used to support an approach by clinicians to collect a complete family history of all cancers - particularly among first degree relatives - in order to assess patient risk for developing cancer."

She also thinks that families who have clusters of different tumours will be helpful to study in order to find out how this happens and pick apart new genetic mutations.

Dr Caitlin Barrand, Senior Policy Manager at Breakthrough Breast Cancer, backs this notion up and recommends women should approach their GP straight away to discuss any fears of family illnesses affecting them.

"If further research confirms the findings of this study, this may further improve our ability to estimate an individual's risk of developing breast cancer, and offer personalised plans to help prevent the disease, or diagnose it early, when it can be more successfully treated," she added.

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