SCIENTISTS CONSIDERING USING DNA TO KEEP TRACK OF LAB WORK

sends the biopsy cells to Strand. The lab matches the DNA from the swab to that of the biopsy cells.

If these DNA fingerprints did not match, that signaled a lab mix-up. That was how pathologists discovered that samples from Erickson and Karman had been switched.

Despite the best efforts of pathologists to avoid these mixups, hints of trouble have been turning up for years.

In 2011, researchers conducting a large clinical trial reported that two men who were found to have prostate cancer — and who had their prostates removed — did not have the disease at all.

Instead, their biopsy samples had been mishandled. (A third mix-up was caught before any action was taken.)

The researchers then performed a rigorous DNA analysis of more than 10,000 biopsies taken during the period. Twenty-seven were mislabeled. Among 6,733 blood samples, 31, or 0.05 percent, had been switched.

The percentage of errors may not be high. But each one may lead a patient down a life-altering path, to a grueling treatment that was unnecessary, or to the neglect of a cancer that may or may not prove deadly.

To really get an idea of the frequency of these mix-ups nationwide, however, Pfeifer needed a large database.

Ted Schenberg, the chief executive at Strand, offered to supply the data: more than 13,000 biopsy results from men evaluated for prostate cancer at a number of laboratories.

Pfeifer agreed to review data, although he knew the company had a significant financial interest in the outcome. To minimize conflicts of interest, Schenberg would not pay him to do the work and would not be involved in the analysis.

Pfeifer documented two types of errors in this large sample: an “absolute switch,” in which one patient’s tissue was mixed up with another’s. And a “partial switch” in which some of one patient’s cells ended up mixed in with cells from someone else.

“Every lab had both of these errors,” Pfeifer said. In general, the rates were low — 0.26 percent of samples were absolute switches, and 0.67 percent were partial switches.

But the rates were slightly higher among independent labs, including large commercial companies that handle huge numbers of specimens: 0.37 percent were absolute switches, and 3.14 percent were contaminated.

Remedying these errors is a costly endeavor. Most private insurers are willing to cover the testing; it’s far less expensive than paying for unnecessary treatment, or treatment late in the course of a disease that should have been identified sooner.

Medicare, on the other hand, does not cover DNA fingerprinting of biopsies, and many of the patients receiving cancer biopsies are older. (Legislation introduced in Congress in May would require the program to cover the service, but only for prostate biopsies.)

Consumers may request DNA fingerprinting themselves, but there is no guarantee that the pathology lab to which their biopsies are sent will offer the service.