One of the first cases came a decade ago, just as the new age of genetics was beginning. A young woman with a strong family history of breast and ovarian cancer enrolled in a study trying to find cancer genes that, when mutated, greatly increase the risk of breast cancer. But the woman, terrified by her family history, also intended to have her breasts removed prophylactically.

Her consent form said she would not be contacted by the researchers. Consent forms are typically written this way because the purpose of such studies is not to provide medical care but to gain new insights. The researchers are not the patients’ doctors.

But in this case, the researchers happened to know about the woman’s plan, and they also knew that their study indicated that she did not have her family’s breast cancer gene. They were horrified.

“We couldn’t sit back and let this woman have her healthy breasts cut off,” said Barbara B. Biesecker, the director of the genetic counseling program at the National Human Genome Research Institute, part of the National Institutes of Health. After consulting the university’s lawyer and ethics committee, the researchers decided they had to breach the consent stipulations and offer the results to the young woman and anyone else in her family who wanted to know if they were likely to have the gene mutation discovered in the study. The entire family — about a dozen people — wanted to know. One by one, they went into a room to be told their result.

“It was a heavy and intense experience,” Dr. Biesecker recalled.

Around the same time, Dr. Gail Jarvik, now a professor of medicine and genome science at the University of Washington, had a similar experience. But her story had a very different ending.

She was an investigator in a study of genes unrelated to breast cancer when the study researchers noticed that members of one family had a breast cancer gene. But because the consent form, which was not from the University of Washington, said no results would be returned, the investigators never told them, arguing that their hands were tied. The researchers said an ethics board — not they — made the rules.