Mammography screenings may be a less valuable breast cancer-detecting tool than thought. A recent study showed that breast cancer screenings are as likely — if not more so — to detect small tumors that will not grow as they are to identify at an early stage potentially dangerous ones.
The study, “Breast-Cancer Tumor Size, Overdiagnosis, and Mammography Screening Effectiveness,” which appeared in the New England Journal of Medicine, also concluded that the improved survival of breast cancer patients is a result of better treatments, rather than earlier detection of deadly cancers.
There is no doubt that mammography does detect potentially deadly cancers. The problem is that screening procedures also detect small tumors that are not destined to grow or spread. And, complicating matters, there is currently no effective way to tell if a tumor will go haywire, or if it will remain small and harmless.
This uncertainty leads to a situation where women get treatment “just in case.” The lead researcher of the study, Dr. H. Gilbert Welch at Geisel School of Medicine at Dartmouth College, refers to mammography as “a value judgment.”
“This is a choice and it’s really important that women understand both sides of the story, the benefits and harms,” he said in a press release. The harm, in this case, most often comes in the form of unnecessary cancer treatment, and the risk of a host of severe side effects.
Welch has long questioned the benefits of mammography screening, and has published other studies supporting his claims.
This time, the research team used data from both mammography surveys and cancer registries to evaluate the number of small (under 2 cm) and large tumors found at mammography screenings. Large tumors are believed to be more dangerous.
They also analyzed death rates in 1975–79, before mammography was introduced, comparing them to rates during the years 2000–02.
Detection of small cancers increased from about one-third during the 70s to two-thirds more recently. This increase was part of an overall jump in tumor detection with mammography, of which the majority were small. Among 100,000 screened women, 162 more cases of small tumors were found via mammographies, and 30 additional large tumors. This finding, the investigators said, implied that mammography contributed to 132 cases per 100,000 women of overdiagnosis.
Researchers then looked into how many deaths were prevented by early detection, comparing that number to prevention tied to better cancer treatments. Confirming earlier studies on the topic, the team found that at least two-thirds of the reduced death rates were linked to better treatments.
Not all scientists agree mammography has lost its value, however. Dr. Kathryn Evers, director of mammography at Fox Chase Cancer Center in Philadelphia, underscores that size alone is not a predictor of a cancer’s aggressiveness, early treatment can prevent death, and mammography is still the method of choice for early detection.
To aid women in their decisions, guidelines propose that women older than age 60 benefit most from screening. Recommendations also advise women to start screening every other year when they turn 50, and that women in their 40s should weigh potential benefits and harms of the procedure. At younger ages, more dense breast tissue makes mammography less valuable. But anyone who feels a lump in the breast is strongly advised to go for a mammogram immediately, and those at higher risk of breast cancer are urged to consider mammograms before age 50.
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