In an analysis of Medicare billing data submitted by more than 2,300 United States physicians, researchers have calculated the average number of surgical slices, or cuts, made during Mohs micrographic surgery (MMS), a procedure that progressively removes thin layers of cancerous skin tissue in a way that minimizes damage to healthy skin and the risks of leaving cancerous tissue behind.

The study, the researchers say, serves as a first step towards identifying best practices for MMS, as well as identifying and informing physicians who may need re–training because their practice patterns deviate far from their peers.

A report of the study, published in the journal JAMA Dermatology April 28, suggests that identifying and informing high outlier physicians of their extreme practice patterns can enable targeted re–training, potentially sparing patients from substandard care.

Ideally, says Makary, those who perform MMS make as few cuts or slices as possible to preserve as much normal tissue as possible while ensuring complete removal of cancers. As each layer of skin is removed, it is examined under a microscope for the presence of cancer cells.

However, there can be wide variation in the average number of cuts made by a physician. Measuring a surgeon’s average number of cuts was recently endorsed by the American College of Mohs Surgery (ACMS) as a clinical quality metric used to assess its members.

Taking their cue from that support, Makary and his research team analyzed Medicare Part B claims data from January 2012 to December 2014 for all physicians who received Medicare payments for MMS procedures on the head, neck, genitalia, hands and feet. These regions of the body account for more than 85 percent of all MMS procedures reimbursed by Medicare during those years.

The researchers found that the average number of cuts among all physicians was 1.74. The median was 1.69 and the range was 1.09 to 4.11 average cuts per case. Of the 2,305 physicians who performed MMS during each of the three years studied, 137 were considered extremely high outliers during at least one of those years. An extremely high outlier was defined as having a personal average of greater than two standard deviations, or 2.41 cuts per case, above all physicians in the study. Forty–nine physicians were persistently high outliers during all three years.

Physicians in solo practice were 2.35 times more likely to be a persistent high outlier than those in a group practice; 4.5 percent of solo practitioners were persistent high outliers compared to 2.1 percent of high outlier physicians who performed MMS in a group practice. Volume of cases per year, practice experience and geographic location were not associated with being a high outlier.

Low extreme outliers, defined as having an average per case in the bottom 2.5 percent of the group distribution, also were identified. Of all physicians in the study, 92 were low outliers in at least one year and 20 were persistently low during all three years.

Potential explanations for high outliers include financial incentive, because the current payment model for MMS pays physicians who do more cuts more money, Makary says. These charges are ultimately passed on to Medicare Part B patients, who are expected to pay 20 percent of their health care bill. Low outliers may be explained by incorrect coding, overly aggressive initial cuts, or choice of tumors for which MMS is not necessary, he says.