While preventive breast cancer screening has led to the detection of more tumors, it has also caused widespread unnecessary treatment for patients, according to a new study conducted by the top cancer researchers.
Since mammography was invented in the late 1970s, the detection of small tumors less than 2 centimeters has increased from 36% to 68%, according to the report published Wednesday in the New England Journal of Medicine. At the same time, the detection of tumors larger than 2 centimeters decreased from 64% to 32%.
Yet, only 30 of the 162 additional small tumors per 100,000 women that were diagnosed were expected to become large. Yet, they are still often treated. The remaining 132 cases of cancer per 100,000 women are overdiagnosed, the researchers found. An estimated 230,000 women in the U.S. are diagnosed with breast cancer each year.
“Mammography isn't able find all the cancers destined to become large, and it also finds cancers that aren't going to become large,” said Dr. H. Gilbert Welch, lead author of the study and a professor of medicine at the Dartmouth Institute for Health Policy & Clinical Practice. Welch is an expert on the issue of overdiagnosis among breast cancer patients and has written extensively on the topic.
For this study, Welch and a team that included researchers from the National Cancer Institute's Division of Cancer Prevention, analyzed federal data on cancer incidence and survival from 1975 to 2012 to determine tumor size and rates of breast cancer among women ages 40 and older.
Overdiagnosis among breast cancer patients is likely prevalent because some providers opt to remove a tumor instead of monitoring its progress. That's a safe way to prevent the disease from progressing, Welch said. “We've overstated the value of screening mammography. We tend to exaggerate its benefits and we haven't been clear about its downside.”
The downside is women can be left with the emotional, physical and often financial toll of treatment that they may not have needed.According to the American Cancer Society, women whose cancer is detected at Stage 1 have a 100% rate of survival over the first five years after initial diagnosis compared with 22% among those whose cancer is not detected until Stage 4.
As a result, overdiagnosis has received more attention from physicians and some have begun the method of “active surveillance,” Welch said. With this tactic, a small tumor is monitored by a physician to see whether or not it progresses to a large, harmful cancer. Small tumors rarely progress. He added that active surveillance is a tactic commonly used for prostate cancer treatment.
The study also found that improved treatment options have contributed far more to fewer deaths among breast cancer patients than mammography. The rate of breast cancer patients dying has decreased by 34% since 1990, according to a 2013 report from the American Cancer Society.
The researchers determined treatment has been responsible for two-thirds of the decrease in breast cancer mortality because the mortality rate has dropped for patients with both large and small tumors, and for women younger than 40 who are rarely screened.
Welch said the findings suggest that for women who don't like to get mammograms shouldn't feel like they have to in order to be safe.
"There is no wrong or right answer to this problem,” he said. “It is a choice and the treatment has gotten a lot better."
Whether to get mammograms has been an ongoing debate over the past few years that's been fueled by conflicting recommendations by the various specialty groups.
