Keeping your doctor up-to-date on cancers in your family could put you on the fast track to screening tests, according to a study that takes a new stab at personalizing preventive medicine.

Researchers found that from age 30 to age 50, the number of people who would be candidates for early colon cancer screening based on family history jumped from two to seven percent.
For breast cancer, the number of women qualifying for earlier and more sensitive screening went up from seven to 11 percent over the same period.

"Doctors should take a family history every five to 10 years," said Dr. Sharon Plon from Baylor College of Medicine in Houston, who worked on the study. "Only taking a good family history the first time you see someone means you will miss important changes."

Having a close relative with cancer often puts people at increased risk of developing the disease themselves. That's why groups such as the American Cancer Society (ACS) have tailored their screening advice according to people's family histories.

For instance, the ACS recommends annual magnetic resonance imaging (MRI) in addition to the less-sensitive mammograms for women between 35 and 60 if they have a first-degree relative diagnosed with breast cancer before age 30.

But those recommendations are not universally accepted, and some researchers say there is little conclusive knowledge about the relative harms and benefits from more-intensive screening.

Widely acknowledged downsides of screening include false alarms that lead to painful, expensive diagnostic procedures, as well as detection of relatively harmless pre-cancerous cells.

"The more we go after these tiny cancers, the more we increase the risk of overdiagnosis," said Dr. Michael LeFevre of the U.S. Preventive Services Task Force (USPSTF), who was not involved in the new work.

Overdiagnosis refers to those tumors that would never have bothered people in the first place — meaning that treatment will do more harm than good.

Still, LeFevre said a person's family history of cancer is an important thing to consider when making screening decisions.

"I certainly think it's appropriate to update the family history periodically," he told Reuters Health. "This article suggests that family history is a moving target."

The study, published in the Journal of the American Medical Association, is the first to test how new cancers in the family influence a person's candidacy for earlier or more-intensive screening.

The researchers used national data from the Cancer Genetics Network, including the family histories for colon, breast and prostate cancer of some 11,000 people.

Looking back at the family histories, the team found the number of candidates for extra screening went up as more cases of cancer surfaced among their relatives.

The jump from two to seven percent for colon cancer, for instance, means that over two decades an additional five out of 100 people would have become early screening candidates if they'd kept their doctors up-to-speed on new cancers in their family.

For breast cancer, an additional four in 100 women would have become early-screening candidates, and for prostate cancer, an additional one in 100 men.

"What we found is that if you take a good family history at age 30, you will only pick up part of the important data and that people's family history of cancer continues to change until they are 50," said Plon, adding that doctors usually do a poor job of taking patients' family histories.

Importantly, however, the study did not test whether screening those new candidates would actually save lives.

An editorial published alongside the new results highlighted questions about the risks and cost of screening.

"It is plausible but still unknown whether family history increases the likelihood that breast cancers, prostate cancers, or colon adenomas found by screening are clinically significant," wrote Dr. Louise Acheson, of Case Western Reserve University School of Medicine in Cleveland.

For instance, she said, adding annual MRI exams to mammograms would increase the cost about 10 times. On the other hand, it's possible that low-risk women in their 40s might choose to forgo screening, Acheson added.

"The benefits, harms, and empirical results of such an approach are ripe for investigation," she noted.