Perhaps farther in the future these clues might lead to new treatments.
"This adds another piece to the puzzle," said Harpal Kumar, chief executive of Cancer Research U.K., the charity that funded much of the research.
One analysis suggests that among men whose family history gives them roughly a 20 percent lifetime risk for prostate cancer, such genetic markers could identify those whose real risk is 60 percent.
The markers also could make a difference for women with BRCA gene mutations, which puts them at high risk for breast cancer. Researchers may be able to separate those whose lifetime risk exceeds 80 percent from women whose risk is about 20 to 50 percent. One doctor said that might mean some women would choose to monitor for cancer rather than taking the drastic step of having healthy breasts removed.
Scientists have found risk markers for the three diseases before, but the new trove doubles the known list, said one author, Douglas Easton of Cambridge University. The discoveries also reveal clues about the biological underpinnings of these cancers, which may pay off someday in better therapies, he said.
Experts not connected with the work said that it was encouraging but that more research was needed to see how useful it would be for guiding patient care. One suggested that using a gene test along with PSA testing and other factors might help determine which men have enough risk of a life-threatening prostate cancer that they should get a biopsy. Many prostate cancers found early are slow growing and won't be fatal, but there is no way to differentiate and many men have surgery they may not need.