More evidence is in this week that casts doubt on the value of mammograms. To recap: Canadian researchers followed nearly 90-thousand women since the 1980s. The women were randomly assigned to mammography or physical breast exam. Now 25 years later, the researchers say that roughly equal numbers of women in each group died of breast cancer — mammography, according to this study, is not affecting the death rate at all.
In addition, mammography comes with harms. More than 1 in 5 cancers found in the mammography group were not ones that pose a threat to women’s health, the researchers say. Doctors call this “overdiagnosis.” This is a problem because the treatments for cancer are aggressive — surgery, radiation therapy, chemotherapy — and can cause harms in and of themselves. “There is no question that there is an excess in the diagnosis of tumors that are not going to kill you,” Dr. Laura Esserman, head of the UC San Francisco breast care center, told me, “We all know this phenomenon exists, but this quantifies it.”
Those are the headlines. Thursday morning, KQED’s Forum got into more detail. I was particularly interested in two points the guests made. The first was about new approaches to screening and the second was about screening as distinguished from prevention.
Need for tailored screening
Right now, various national organizations have published guidelines about screening. For example, the American Cancer Society recommends that women be screened annually starting at age 40 and continuing as long as she “is in good health.” The U.S. Preventive Services Task Force says that women ages 50-74 should be screened every other year. For women younger than 50, the USPSTF says, the decision to have a mammogram every other year is an “individual one.” The USPSTF also said there was not enough evidence to make a recommendation for women 75 and older.
Most of the debate about mammograms is revolves around whether they should be done every year — or every other year. But the guests on Forum argued for something different. “We need to move in a new direction,” said Karla Kerlikowske, a UCSF professor of medicine and a leading researcher about mammograms. “We need to focus on who’s at high risk and really tailor screening” — not just looking at age cutoffs.
She cited several factors that increase a woman’s risk: diagnosed breast density, family history, hormone use. While breast cancer risk generally increases with age, when you factor in these other variables, individual women may get a different picture. Some women in their 40s may have a higher risk than a woman in her 60s. By comparison, a woman in her 60s may actually be at low risk. “Risk assessment helps us to target those high-risk people,” Kerlikowske said.
Dr. Susan Kutner, who chairs Kaiser Permanente’s northern California breast care task force, said that in Kaiser “we recommend that every woman have a discussion with her physician” about risk factors, health factors and the benefits and harms of screening.
(If you want to do a quick assessment of your risk, you can start with this tool from the National Cancer Institute. It should take you less than 5 minutes.)
Screening vs. Prevention
Both Kerlikowske and Kutner talked about the need for a better screening test. “One of the things all of these studies are telling us is that we don’t have a perfect test,” Kutner said. “Adding additional imaging may just find those small cancers that will never affect a woman’s quality or quantity of life.”
Kerlikowske contrasted the mammogram with colonoscopy. “In colon cancer you remove the polyp and decreases the risk of colon cancer. We don’t have that paradigm in breast cancer.” It’s the same with cervical cancer screening. The Pap test helps find pre-cancerous lesions, which when removed, reduce a woman’s risk of developing cervical cancer.
In breast cancer staging, the “Stage 0” breast cancer is called ductal carcinoma in situ — or DCIS. “Everyone had hoped DCIS was that (precancerous) lesion, but it’s not, for most breast cancers,” Kerlikowske said. “It’s a risk factor for breast cancer, but it’s not a precursor.” The problem? Kerlikowske notes that DCIS has been treated for “25 years, but there’s no change in breast cancer incidence and it doesn’t decrease breast cancer mortality” according to this most recent study. Some women are choosing “active surveillance” as opposed to treatment when diagnosed with DCIS.
Right at the end of the show, Kerlikowske ticked off a short list of things women could do to reduce their breast cancer risk. In particular, she cited maintaining an “ideal body weight,” exercise and avoiding long term hormone use. Other things in a woman’s control are limiting alcohol intake.
Exercise and maintaining a healthy weight will help women reduce their risk of heart disease too — their number one killer. About 400,000 women die each year from cardiovascular disease; about 40,000 from breast cancer.
This is one more study to raise questions about how mammography should be used. For now, current screening guidelines remain in place. NPR reports that both the American Cancer Society and the U.S. task force are reviewing evidence with possible changes to their guidelines coming — perhaps as early as later this year.
Listen to Professor Kerlikowske and Dr. Kutner on Forum: