Strict adherence to pathology guidelines for interpreting immumohistochemical (IHC) staining in endometrial cancer samples may miss the opportunity to identify patients with Lynch syndrome, investigators cautioned.
Current College of American Pathologists recommendations say that any partial, indeterminate, or “heterogeneous” IHC staining for DNA mismatch repair proteins (MMRP) should be considered as intact expression staining.
However, a retrospective review of patients with endometrial cancer showed that 3 of 13 patients with Lynch syndrome had a small proportion of staining and would have been considered at low risk for Lynch syndrome if the reporting rules were followed to the letter, according to Courtney J. Riedinger, MD, and colleagues from the University of Tennessee Medical Center in Knoxville.
“IHC staining for mismatch repair proteins is a way to screen for who should get genetic testing [for Lynch syndrome],” Dr. Riedinger said in an interview. “The pathology guidelines say that any expression is intact staining, but we found some tumor specimens that have about only 20% staining, and we found that 3 of 27 patients with a range of 20%-60% expression had Lynch syndrome.”
The findings suggest that genetic testing for Lynch syndrome should be considered in patients with heterogeneous staining for MMRP, Dr. Riedinger and colleagues wrote in an abstract that had been slated for presentation at the Society of Gynecologic Oncology’s Annual Meeting on Women’s Cancer. The meeting was canceled due to the COVID-19 pandemic.A recent systematic review estimated the prevalence of Lynch syndrome in women with endometrial cancer to be 3%. The authors of the review recommended universal screening for Lynch syndrome in women with endometrial cancer (Genet Med. 2019 Oct;21[10]:2167-2180).
As Dr. Riedinger and colleagues noted, screening for Lynch syndrome can be performed clinically with microsatellite instability testing or IHC staining for MMRP.
To determine the frequency of Lynch syndrome in women with endometrial cancer whose samples exhibited heterogeneous staining for MMRP, the investigators conducted a retrospective review.
They identified 455 women who underwent hysterectomy for endometrial cancer during 2012-2017. Of this group, samples from 315 patients had no MMRP loss, 92 had complete loss, and 48 had heterogeneous MMRP staining. Of the latter group, 21 samples were reported as intact, and 27 were reported as heterogeneous.
A total of 13 patients were identified as having Lynch syndrome, including 3 of the 27 patients with reported heterogeneous staining and 10 with reported complete loss of MMRP.
The investigators found the frequency of Lynch syndrome among patients with reported heterogeneous staining was not significantly different than that for patients with complete MMRP loss. In addition, there were no significant differences between samples with heterogeneous or complete loss of staining by type of MMRP.
“Our data suggest genetic testing for Lynch syndrome in patients with heterogeneous IHC staining for MMRP should be considered. Current reporting guidelines regarding MMRP expression in endometrial cancer patients need to be reevaluated,” Dr. Riedinger and colleagues concluded.
Dr. Riedinger reported no conflicts of interest. The study was internally funded.
SOURCE: Riedinger CJ et al. SGO 2020, Abstract 104.