Ability To Read Mammograms Varies Widely

April 20, 1998

The mammogram-reading skills of general radiologists vary enormously according to a study to be presented Monday, April 20, at the 28th National Conference on Breast Cancer in Washington, DC. Although the researchers who performed the research were impressed with the overall ability of most general radiologists, they were troubled by the magnitude of the variance.

Seventy-five general radiologists detected, on average, 70 percent of 50 breast cancers visible on 100 mammograms, about what previous studies would predict. Three expert mammographers detected 81 percent. All the experts all had similar scores, ranging from 76 percent to 86 percent. For the generalists, however, scores ranged from a high of 98 percent -- with a lot of false positives (normal exams rated as cancerous) -- to a low of eight percent.

"The generalists' scores were all over the map," said Robert Schmidt, M.D., associate professor of radiology at the University of Chicago and director of the study, "rather than clustered around 70 percent. The average score was no surprise. Most previous studies suggest that 15 to 30 percent of cancers are not detected at the first opportunity. But the extreme range was an eye opener."

Moreover, there was only a weak correlation between the test results for each generalist and his or her self-assessed level of expertise. For example, some of those who classified themselves as having advanced skills, scored lower than those who rated themselves as novices.

"Imaging technology has steadily improved and continues to get better," said Schmidt. "Now, the human observer may often be the weakest link in the breast-imaging chain."

Most quality-of-care research is performed at academic centers and focuses of the talents of highly specialized experts who devote their careers to a few specific interests, such as mammography.

The majority of screening mammograms, however, are read by general radiologists, who may read as few as two mammograms a day.

The researchers -- from the University of Chicago, New York University, University of New Mexico at Albuquerque, and University of Illinois at Peoria -- presented high-quality films from 100 mammography cases to 100 radiologists who were attending continuing medical education meetings, and to four mammography experts.

Each radiologist was given two-and-one-half hours to complete the exercise, conditions roughly comparable to a routine clinical situation, except for the higher percentage of cancers. Ordinarily, there is only about one cancer per 1,000 screening mammograms.

The 100 films contained 55 normal cases and 45 cases with at least one cancer. (Five cases had two cancers). The observers were asked to rate the cases as normal or abnormal and to indicate the location of a lesion. The cancers were typical lesions found by routine screening mammograms, not unusually difficult or "tricky" cases.

Only 75 percent of each group of radiologists finished the task. Those who completed fewer than 90 of the 100 cases were not included in the final assessment, "but they clearly would not have improved the scores," noted Schmidt. Those who did not complete the test found only 42 percent of the cancers in the cases they completed.

The experts detected 16 percent more cancers than generalists. Experts, however, were slightly more likely to rate normal cases as abnormal.

"Dedicated mammographers seemed to have a lower threshold for what they find suspicious than generalists," said Schmidt. "They found significantly more cancers but wanted to take a closer look at more women who did not have cancers."

Although the 70-percent detection rate may seem low, "reading mammograms is extremely difficult, even for the experts," cautioned Schmidt. It requires a lot of training and experience. "Very few people who don't do it full-time develop the skills to do it at the highest levels."

That's because reading screening mammograms is very different from other tasks performed by radiologists. Instead of looking for the cause of symptoms in a sick person, screening studies look for signs of minute, pre-symptomatic disease in healthy patients. It requires a different mind-set, says Schmidt, and different sets of behaviors.

"The good news," added Schmidt, "is that this is a problem we know how to solve. We can teach generalists to read these images consistently and with a level of accuracy level closer to that of the experts. But we need to develop methods to make this training more accessible to all radiologists."

On one case, 85 percent of the generalists missed a cancer found by 100 percent of the experts. "As you might expect, we now use that as a teaching case," emphasized Schmidt.

Ongoing technology improvements will also help. Digital mammography units, which enable physicians to manipulate the images in new ways, are entering the market. And researchers at the University of Chicago have developed a computer that read mammograms, providing a second opinion for the radiologist and cutting the error rate.

Until these technical advances become more common, Schmidt recommends that women seek breast programs at academic institutions or specialized breast diagnostic centers with dedicated mammographers, who are more likely to have the advanced training and experience.

The American Cancer Society estimates that 178,700 women will be diagnosed with invasive breast cancer in the United States in 1998 and 43,900 women will die from the disease. About one in eight American women will develop the disease by age 85. Mammography is the only known method that can find small, curable cancers before they can be felt, and has been shown to significantly decrease deaths from breast cancer.

University of Chicago Medical Center

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