Mammografieën en de kans op borstkanker?*
Uit een Nederlandse analyse van zes verschillende studies blijkt dat bij vrouwen, die een verhoogde kans op borstkanker hebben als gevolg van erfelijke aanleg, door een lage dosis straling van een jaarlijkse mammografie het risico op borstkanker duidelijk verhoogd wordt.
Vier studies keken naar het effect van de blootstelling aan lage doses straling tussen borstkanker-gen mutatiedragers en twee studies onderzochten het effect van straling op vrouwen met een familiegeschiedenis van borstkanker. Gemiddeld was als gevolg van de lage straling van mammografieën de kans op borstkanker bij deze vrouwen 150% hoger. Bij vrouwen jonger dan 20 jaar of zij die al 5 keer een mammografie gehad hadden was de hogere kans zelfs 250%, vergeleken met zij die geen mammografieën lieten nemen.
Voor vrouwen met een hoog risico op borstkanker is screening belangrijk doch het is oppassen met mammografieën zeker bij vrouwen jonger dan 30 jaar. Herhaalde blootstelling aan lage doses straling moet worden vermeden", zegt Dr Marijke C. Jansen-van der Weide, epidemioloog bij de afdeling Epidemiologie en Radiologie van Universitair Medisch Centrum Groningen in Nederland. Zij adviseert deze groep vrouwen goed te overleggen met hun behandelende arts over te volgen aanpak.
Study Questions Safety of Mammograms for Young Women at High Risk of Cancer
For young women who have a high risk of breast cancer because of genetic mutations or family history, the radiation from yearly mammograms may make the risk even higher, researchers reported at a radiology conference on Monday.
The report is particularly troubling because it suggests that the very women who are told they need mammograms most may also be the most vulnerable to harm from them. Doctors routinely urge high-risk women to have mammograms earlier in life and more often than women judged to be at average risk.
Researchers caution that the new report is not conclusive, and that the issue needs more study.
High doses of radiation can increase the risk of breast cancer, especially in young women, but mammography uses a low dose. The American Cancer Society and many breast cancer experts say the benefits of screening far outweigh any theoretical risk from the radiation.
But the new findings will probably fuel the debate that was ignited by a recent article in The Journal of the American Medical Association questioning the value of breast cancer screening and a report by a government task force suggesting that most women could start having mammograms later in life and repeat them less often than had generally been recommended.
The latest findings come not from new research, but from an analysis that pooled the data from six earlier studies involving about 5,000 high-risk women in the United States and Europe, some who had breast cancer and some who did not. Their median age was 45.
Looking back at their medical histories, researchers found that those women who had had mammograms or chest X-rays (which use a lower radiation dose than mammography) were more likely to have breast cancer.
Specifically, women exposed to radiation before age 20 or women with five or more exposures were 2.5 times more likely to develop breast cancer than were women who had not been exposed. The difference was statistically significant after all the data was pooled, but only some of the individual studies had significant findings; in those that did not reach statistical significance, the results could have been due to chance.
The analysis applies only to women who, like those in the study, have a high risk of breast cancer — about 0.5 percent to 1 percent of the population.
Marijke C. Jansen-van der Weide, the first author of the study and an epidemiologist at University Medical Center Groningen in the Netherlands, presented the analysis in Chicago at a meeting of the Radiological Society of North America.
In a telephone interview, Dr. Jansen-van der Weide said it was of concern to find a doubling of risk in women whose baseline risk was already high, and she suggested that young women at high risk should avoid repeated exposure to even low-dose radiation. She said the same mutation that increased the risk of breast cancer might make the breast more susceptible to cancer caused by radiation.
“For high-risk women, it’s important to weigh the benefits and risks of mammography with their doctor and come together on a screening strategy, and to keep in mind that at a young age you can use an alternative screening technique like M.R.I.,” Dr. Jansen-van der Weide said.
Robert Smith, director of cancer screening for the American Cancer Society, questioned the analysis’ methodology and disagreed with the idea that M.R.I. could replace mammography in high-risk women. Dr. Smith said M.R.I. missed some tumors that mammography could find, and vice versa, so the best approach for high-risk women was to use the two tests together.
“It’s not as if clinicians are unaware and unconcerned about radiation risks in young women,” he said. “If mammography offered no advantage, they wouldn’t do
it.” (December 2009)
