More than 80 percent of those who are genetically predisposed to have cancer are unaware about their risk, a study of over 50,000 people has found.

In the absence of routine screening, most people only discover they carry cancer-associated variants in the BRCA1 or BRCA2 genes when that person or family members receive a cancer diagnosis.

"As a colleague said, it usually takes a tragedy for people to get tested," said Michael Murray, a professor at Yale University in the US.

"Our reliance on a documented personal or family history as a trigger to offer testing is not working. Hopefully, one day we can change that with effective DNA-based screening for everyone," said Murray.

The mean age of subjects in the study was 60. Two hundred and sixty-seven of those screened possessed a BRCA risk variant, yet only 18 percent of them were aware they possessed this risk factor for cancer prior to being informed by the study.

Among the group of living BRCA-positive patients, 16.8 percent of them had a BRCA-associated cancer. In the small group of BRCA-positive patients who had died before the study's conclusion, 47.8 percent of them had a BRCA-associated cancer.

"Once risk is identified, we can apply proven tools for early diagnosis and prevention, and we believe that the 31 percent difference in cancer incidence in these two groups is a window into an opportunity to decrease cancer and cancer deaths through genomic screening approaches," Murray said.