Mammograms are not always an effective way of diagnosing breast cancer, and the accuracy of a mammogram is highly dependent on the physician who reads it. A new three-state study led by Seattle’s Group Health Cooperative revealed that even the most skilled radiologists fail to detect 20 percent of breast-cancer cases in diagnostic mammograms, which are conducted when cancer is suspected and when tumors would presumably be larger and easier to spot. This revelation strengthens concerns about relying on a mammogram, which experts have long said was an imprecise tool for detecting breast cancer, and confirms that women shouldn’t automatically accept a mammogram result—whether negative or positive—as the final word.
Researchers examined nearly 36,000 mammograms read by 123 radiologists and found a woman’s odds of receiving accurate results were dependent on who conducted the reading. In the worst cases, radiologists missed nearly 40 percent of the tumors and misidentified 8.3 percent of their patients as having nonexistent cancers. Top performers tended to be doctors at academic medical centers and breast imaging specialist. Even so, cancer went undetected in one of five women did have cancer and 2.6 percent received false-positive results. Those who spent at least 20 percent of their time on breast imaging caught 80 percent of cancers, compared with 70 percent for those with lesser focus—a difference researchers said is probably not due to chance. Affiliation with academic medical centers was the single greatest factor in successful cancer-detection rates; however, only seven of the 123 radiologists fit that criterion. Conversely, the sheer number of mammograms read did not meaningfully raise a radiologist’s performance. The researchers suggested creating imaging centers staffed by radiologists who specialize in breast imaging.
Women are warned to not interpret the study as an indictment against mammograms in general since routine mammograms do reduce death rates from breast cancer—a disease that kills nearly 40,000 Americans yearly—among women over 50.
What remains unclear is the benefit to symptom-free younger women from screening. Regardless, women of any age receiving mammograms should request radiologists who only handle breast imaging.
The findings come as some health experts’ opinions are diverging on the value of mammograms, particularly for younger women. In April, an influential physicians group came out against the wide practice of giving annual mammograms for women 40 to 49, saying women within that age group aren’t at a uniform risk of cancer and the mammograms themselves could expose the women to harm through needless treatments because of a false cancer scare.
While mammography is not perfect, it is considered the best diagnostic tool in the detection of breast cancer. Traditional mammograms, taken with low-dose X-rays, are notoriously difficult to read. Benign and malignant lesions can look alike, a speck of tumor can be hard to discern from the surrounding breast tissue, and accurate readings rest largely on a radiologist skill.
The study’s findings on diagnostic mammograms echo previous research on screening mammograms, which many women receive annually starting at age 40. Diagnostic mammograms, by contrast, are performed when a lump or something unusual is discovered in the breast. Of every 1,000 woman undergoing diagnostic mammograms, 44 will have cancer, compared with five women receiving screening mammograms.
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