Another Level of Complexity
At the immunotherapy session in San Antonio, Rimm discussed the results of a study of 68 TNBC archived cases in which specimens were stained with the SP142 assay at Yale and were distributed via electronic images to 19 pathologists at 14 institutions across the United States for PD-L1 scoring.
The study, coauthored by academics from Iowa, Texas A&M, UC San Diego, Mayo Clinic, Memorial Sloan Kettering, and others, used a novel method to determine the minimum number of evaluators needed to estimate “concordance” or agreement about a test result among large numbers of readers. The consensus/agreement was as high as 80% when eight or fewer pathologists’ scores were compared, but was as low as 40% when results from more than eight pathologists were included, said Rimm.
These are some of the data that led him to declare that using the assay is no better than flipping a coin.
Yes, PD-L1 testing is a challenge, and it has “introduced another level of complexity” for pathologists in reading assays, write experts Emina Torlakovic, MD, University of Saskatchewan, Canada, and Allen Gown, MD, PhenoPath Laboratories, Seattle, in response to Rimm last year.
But there is “poor” consensus among pathologists, they point out, “for many scoring systems that are still clinically applied (such as Gleason grading).” Consensus “improves with education and training,” the pair add. To that end, Roche has initiated a global training program for pathologists using the SP142 assay for TNBC. At San Antonio, Roche’s Dennis reported that among 432 pathologists from 58 countries, there was overall agreement of 98.2% in scoring assays.
Rimm commented that such high agreement would not be a surprise if testing took place soon after any such training program.
In an email to Medscape Medical News, Torlakovic encouraged pathologists who wish to practice their skill in interpreting assays, including SP142, to visit CBQAReadout.ca, a testing site. The site, which was founded by Torlakovic and may be one of a kind, offers CME credits and is sponsored by independent pathology organizations, such as CAP-ACP and the Saskatchewan Health Authority, as well as pharmaceutical companies, including Roche.
No Clue
Patient advocate Cowden believes the controversy about PD-L1 testing for atezolizumab is largely unknown among breast cancer patients. She learned about SP142 assay ambiguities in San Antonio, when the Florida Breast Cancer Foundation funded her trip to the meeting and the Alamo Breast Cancer Foundation asked her to write a report on Rimm’s presentation.
Cowden is a member of a Facebook group for stage IV TNBC, which has about 1500 members. She estimates that 75%-80% would be willing to try atezolizumab “no matter what,” meaning they don’t care about PD-L1 positivity being associated with efficacy.
The Facebook group members “know there is a test and if you are positive, there is an immunotherapy for their breast cancer,” said Cowden.
None know that women may be excluded from treatment because of shortcomings with the SP142 test. “They have no clue,” she said.
Rimm and DeMichele have financial ties to Roche and other companies. Dennis is an employee of Roche. Torlakovic has ties to multiple companies, including Roche, for whom she has acted as a paid consultant, grant recipient, and paid lecturer. Gown did not respond to a request for financial disclosures. Cowden reports no relevant financial relationships.
This article first appeared on Medscape.com.
