Making sense of overdiagnosis

Overdiagnosis has long been a central focus of the debate surrounding breast cancer screening schedules. According to a recent article for Academic Radiology, the root cause of overdiagnosis is an “information problem.”

“We do not have perfect information in medicine,” wrote Saurabh Jha, MD, of the department of radiology at the University of Pennsylvania. “If we did, we could use the right test in the right patient to reach the right diagnosis so that we could administer the right treatment in the right amount leading to neither underdiagnosis and undertreatment nor overdiagnosis and overtreatment.”

Jha explained that overdiagnosis comes down to considering three things:

  1. “Many patients will not be harmed”
  2. “Some patients will be harmed”
  3. “At the time of decision making, we do not know, with an acceptable level of confidence, who will and will not be harmed.”

The information problem is caused by the inability to know which patients will be harmed and which will not. Some patients with papillary carcinoma of the thyroid, for instance, will be harmed by that tumor; others with the same tumor will never be harmed. But surgery for the tumor will put the patient at risk, and patients who would have not been harmed by the tumor could then be harmed by the surgery.

Jha wrote that this is where underdiagnosis and undertreatment come into play. When worrying about overdiagnosis, it’s also possible to go too far and instead be responsible for underdiagnosis. It’s a balance physicians in modern societies deal with on a daily basis.

“This duality, which cannot be overemphasized, is seldom explicitly stated,” Jha wrote. “The reason why the debate in screening for breast cancer is intractable is that both sides are correct. Screening extends longevity, but screening overdiagnoses. We could reframe the dialectic: screening overdiagnoses, but screening extends longevity.”

Setting thresholds for suspicion of disease—a point presently at the center of discussions focused on breast density reporting laws—is extremely important when looking at overdiagnosis, according to Jha.

“This threshold is a gateway to overdiagnosis,” Jha wrote. “Theoretically, where we set the threshold for suspicion of disease should not affect the amount of overdiagnosis, but in reality, it does. The lower we set the bar for suspicion of disease, the more we overdiagnose.”

New research, same debate

A study published in JAMA Internal Medicine earlier this month brought some extra attention to overdiagnosis. Looking at the effects of regular mammograms on a group of 16 million women, data scientist Charles Harding and colleagues found that an increase of mammograms performed in any area would increase the number of small tumors and precancerous tumors found in that area, but it would not increase the number of larger tumors or breast cancer-related deaths.

“When directed toward the general U.S. population, the most prominent effect of screening mammography is overdiagnosis,” the authors wrote.

With so much scientific research and public discourse focusing on the topic of breast cancer screenings, the debate over overdiagnosis is unlikely to end any time soon.