TUESDAY, Aug. 20, 2002 (HealthDayNews) -- The risk of breast cancer associated with two inherited gene mutations is probably much lower than previously believed, new research now says.
The reasons involve highly technical epidemiology, but the bottom line is this: Earlier studies probably overestimated the contribution to cancer risk of the two mutations, while downplaying the importance of other, yet undiscovered genetic factors.
Ever since the discovery in the mid-1990s of the BRCA1 and BRCA2 breast and ovarian cancer mutations, women have lived in fear of inheriting the errant genes.
Cancer geneticists had previously estimated the risk of breast cancer associated with these mutations at between 70 percent and 85 percent by age 70 for women who have close relatives with the disease.
As a result, those who test positive for the flaws, which are particularly common in Jewish women of Eastern European heritage, often opt for breast removal surgery or preventive drug treatment to reduce their risk.
According to the new research, the risk is still "considerably elevated, but it's not a life sentence," says Colin Begg, an epidemiologist at Memorial Sloan-Kettering Cancer Center in New York City and author of the study. "The evidence suggests that there's considerable variability in risk even among individuals who have the BRCA mutations."
Begg's study hinges on a phenomenon called penetrance. When expressed as a percentage, this term refers to the likelihood that a carrier of a disease mutation will develop the condition. Knowing the penetrance of a particular cancer gene, for example, can help genetic counselors advise carriers of that mutation how best to protect themselves against illness.
Although Begg didn't calculate a figure for the true penetrance of BRCA mutations for breast cancer, research shows it could be as low as 26 percent for some women, or perhaps even lower.
While that's about three times the average woman's lifetime risk of the disease, estimated at 8 percent, it may not warrant radical medical procedures, he says.
Begg, whose research appears in tomorrow's issue of the Journal of the National Cancer Institute, says the implications of the findings will become weightier as more women seek genetic testing. Now, most of those getting tested for BRCA errors have family members with breast or ovarian tumors, and thus are at high risk for the diseases.
"But we're moving into an era when testing is likely to be commonplace, and a lot of people are going to get it. Preventive options like prophylactic mastectomy make much less sense" for women whose risk of breast cancer isn't soaring, he says. Instead, he adds, they may do well with regular mammograms, self-exams and other prudent monitoring.
Karolynn Siegel, a Columbia University public health researcher who specializes in coping with chronic illnesses, says people "cling to anything that gives them more hope."
So revising the risk of inherited breast cancer downward might help some women breathe easier, she adds.
"There are other factors that come into play, so women don't have to feel that genetics is destiny," Siegel says. The difficulty, however, is that scientists aren't certain what these factors are, though they seem to include lifestyle habits such as diet, exercise and smoking.
Ruby Senie, a Columbia University cancer epidemiologist, says several recent studies have hinted that the risk of breast cancer from BRCA1 and BRCA2 errors might be lower than previously suspected. Also, studies of women with strong family histories of breast cancer but who test negative for these mutations are powerful evidence that other gene flaws almost certainly are involved in the disease, she adds.
Ultimately, Senie says, women simply want to know what it means when they're told they carry a cancer mutation -- and right now science can't say.
What To Do
For more on breast cancer, visit Breast Cancer Week. To find out more about inherited cancers, visit FORCE, a support group for people with cancer genes.
