Parallel screening for ALK, MET and ROS1 alterations in non-small cell lung cancer with implications for daily routine testing.

Abstract

ALK, MET and ROS1 are prognostic and predictive markers in NSCLC, which need to be implemented in daily routine. To evaluate different detection approaches and scoring systems for optimal stratification of patients eligible for mutation testing in the future, we screened a large and unselected cohort of NSCLCs for all three alterations. Using tissue microarrays, 473 surgically resected NSCLCs were tested for ALK and MET expression by IHC and genomic alterations in the ALK, MET and ROS1 gene by FISH. For MET IHC, two different criteria (MetMAb and H-score), for MET FISH, three different scoring systems (UCCC, Cappuzzo, PathVysion) were investigated. ALK and ROS1 positivity was seen in 2.6% and 1.3% of all ADCs, respectively, but not in pure SCCs. One ROS1 translocated tumor showed additional ROS1 amplification. MET IHC+/FISH+ cases were found in both histological subtypes (8.6% in all NSCLCs; 10.6% in ADCs; 5.0% in SCCs) and were associated with pleural invasion, lymphatic vessel invasion and lymph node metastasis. MET altered ADCs more frequently showed a papillary growth pattern. Whereas ALK testing revealed homogenous results in IHC and FISH, we saw discordant results for MET in about 10% of cases. Both METIHC scoring systems revealed almost identical results. We did not encounter any combined FISH positivity for ALK, MET or ROS1. However, three ALK positive cases harbored MET overexpression. In daily routine, IHC could support FISH in the identification of ALK altered NSCLCs. Further research is needed to assess the role of discordant MET results by means of IHC and FISH as well as the relevance of tumors with an increased ROS1 gene copy number.