Delaying starting age for mammography won’t reduce overdiagnoses

A survey of almost six million breast exams found not one case of untreated cancer had regressed by the next mammogram—refuting the notion that overdiagnosis could be reduced by delaying the starting age for mammography screening or increasing the interval between exams. The study sampled outcomes data from 40 Society of Breast Imaging fellows and was published in the Journal of the American College of Radiology.

Critics of screening mammography often cite the danger of overdiagnosis as a chief harm and a reason to potentially reduce screening, according to the article. However, it’s difficult to measure; an untreated cancer found on mammography will still look suspicious enough to be flagged during the next exam, calling into question if reducing mammography would really trim overdiagnosis.

While breast imagers are generally familiar with cancer’s staying power, according to the article, Arleo and her fellow researchers wanted to go beyond anecdotal evidence and collect large-scale data. After surveying the fellows and collecting data on 6,865,324 breast exams over the past 10 years, the researchers found 240 cases of untreated screen-detected invasive breast cancers—not one was reported to have disappeared or regressed.

“If a woman starts screening at age 40, an overdiagnosed lesion could be detected and overtreated when she is 40; however, if this woman instead starts screening at age 50, that same overdiagnosed lesion will still be visible and will still be detected and overtreated when she is 50,” wrote lead author Elizabeth K. Arleo, MD, assistant professor of radiology at Weil Cornell Medical College, et al. “Second, if a woman undergoes annual screening mammography, an overdiagnosed lesion may be detected and overtreated in an odd-numbered year; however, if her screening is instead biennial, only in even-numbered years, this same lesion will be detected and overtreated a year later. In either case, reducing the frequency of screening does not reduce the frequency of overdiagnosis because the overdiagnosed lesions will still be detected and interpreted as suspicious for malignancy, as our study results demonstrate.”

Delaying the detection of cancer is problematic. If women don’t undergo screening until 45 or 50 years old, the cancer will be more difficult and expensive to treat by the time it’s finally found. In addition, it’s impossible to know which cancers will remain the same size versus which will grow to a more advanced stage. This causes most physicians to err on the side of caution and treat all cases of biopsy-proven breast cancer.

While this will inevitably result in overtreatment, that’s a favorable alternative to reducing mammography as a whole, according to Arleo et al.

“Although some organizations have suggested that the risk for overdiagnosis and overtreatment may be increased by earlier or more frequent screening, our study results demonstrate the fallacy of this suggestion,” the authors wrote. “The take-home message for organizations making screening mammography guidelines is that overdiagnosis is not mitigated by later-onset or less frequent screening.”