A new study conducted by researchers at the Yale School of Medicine reveals that small tumors found in the breast during screenings are not small because they are discovered early, but biologically prone to slow growth.
“For over 100 years, we’ve known that small breast cancers have a much better prognosis than large breast cancers,” said lead author of the study Donald Lannin, a professor of surgery at the Yale School of Medicine. “We always assumed that it was because we were catching the small cancers early and then that’s why the cure rate was much better.”
During the study, the research team examined thousands of breast cancer cases collected by the National Cancer Institute’s Surveillance, Epidemiology and End Results database between 2001 and 2013.
The researchers discovered that nearly 22 percent tumors detected by mammography are prone to slow growth. Factors, such as whether a tumor’s growth is altered when exposed to hormones.
“We thought almost all breast cancers were alike. You know, a breast cancer was breast cancer – it was bad,” said Lannin.
Breast cancer differs “tremendously,” while some types of cancers are extremely slow growing, others are extremely aggressive and fast growing, Lannin says.
“It takes 15 to 20 years of [these small tumors] to cause any problems. And you can king of imagine that a lot of patients will die of something else over that 15 or 20 years,” Lannin explains.
A large number of women who undergo mammograms will go through biopsies, chemotherapy, radiation and/or surgery for harmless tumors that will probably never pose a health threat.
H. Gilbert Welch, MD, MPH, a professor of medicine, community and family medicine at Dartmouth College, said it seems that “screening disproportionately finds good cancers – cancers that may be better off not found.” Welcome did not participate in the new study.
“I think that we all need to realize that we’ve probably oversold the idea that looking for cancer early is the way to avoid it,” Welch says. “Mammography’s a really close call. It’s a choice. We’ve exaggerated its benefit and we’ve sort of understand its harms.”
Just recently, the American Cancer Society scaled back their mammogram guidelines and are now saying that women can hold off screenings until they are 45, at which time they can start getting screened annually.
Otis Brawley, chief medical officer at the American Cancer Association, recommends for women to continue following the current guidelines.
The study was published in The New England Journal of Medicine on June 8, 2017.