J Mol Diagn. 2020 Oct 1:S1525-1578(20)30482-7. doi: 10.1016/j.jmoldx.2020.09.006. Online ahead of print.
Detecting ALK and ROS1 protein expression by immunohistochemistry (IHC) is required to select patients for targeted treatment in non-small cell lung cancer. This study evaluated staining performance for different IHC protocols and laboratory characteristics, and their influence on ALK and ROS1 interpretation during external quality assessment (EQA) schemes between 2015-2018. Participants received five formalin-fixed paraffin-embedded cases for staining by their routine protocol, where after at
least two pathologists scored them simultaneously under a multi-head microscope and awarded a graded expert staining score (ESS) from 1-5 points based on the staining quality. CE-IVD kits (such as D5F3) revealed a better ALK ESS compared to laboratory developed tests. The ESS was not affected by the applied antibody dilution or a recent protocol change. Lower ESS were observed for higher antibody incubation times and temperatures. There were no major differences in ESS for the various ROS1 protocols. Overall, for both markers ESS improved over time and upon repeated EQA participation, but did not depend on laboratory setting or experience. Except for ROS1, ESS positively correlated with laboratory accreditation. IHC stains with lower ESS correlated with increased error rates in ALK and ROS1 interpretation and analysis failures. Staining performances increased, but need improvement in case of less common protocols. Laboratory characteristics differently affected staining quality and interpretation, and laboratories are recommended to assess both aspects.