Correlating ROS1 Protein Expression With ROS1 Fusions, Amplifications, and Mutations

Abstract

Introduction: In this study, we sought to further characterize ROS1 protein expression in solid tumors with the complete spectrum of ROS1 genomic alterations. Methods: ROS1 immunohistochemistry (IHC) was performed using the ROS1 (SP384) class I assay per manufacturer's instructions on a variety of solid tumors (n ¼ 32) with known ROS1 genomic alterations. Genomic alterations included fusions (n ¼ 17), gene amplifications (n ¼ 10), and short-variant mutations (n ¼ 11). Results: Of the 32 cases with ROS1 IHC results, 100% (11 of 11) with canonical ROS1 fusions were positive for ROS1 IHC. Among noncanonical ROS1 fusions, only two (of five) cases with SQSTM1-ROS1 and RDX-ROS1 fusions were positive for ROS1 IHC whereas PTPRK-ROS1 (two) and TTC28-ROS1 fusions were negative for ROS1 IHC. One sample with a canonical ROS1 fusion and co-occurring ROS1 resistance mutation (6094G>A, p.G2032R) was positive for ROS1 IHC. A total of 10% (one of 10) of ROS1 amplified tumors were positive for ROS1 IHC. None of the cases (zero of five) with ROS1 short-variant mutations were positive for ROS1 protein expression. Conclusions: These findings suggest that if ROS1 IHC was used as a screening tool for ROS1 fusion, a subset of fusionnegative tumors will reveal positive IHC staining highlighting the value of reflexing to genomic profiling to confirm the presence of a targetable fusion-driver before the initiation of therapy. In addition, the ability of comprehensive genomic profiling to detect ROS1 resistance mutations will be important for clinical decision making.

Pan-cancer analysis of CD274 (PD-L1) mutations in 314,631 patient samples and subset correlation with PD-L1 protein expression

“…In terms of CD274 missense mutations, these could mediate resistance to ICPI due to potential steric or affinity-altering interferences in the binding of the PD-L1 ligand to the PD-1 receptor, similar to a resistance mechanism described for ROS1 , though further studies are needed to evaluate this hypothesis. 28 29 In our cohort of cases with CD274 missense mutations, we observed a slightly lower level of PD-L1 IHC staining in the cases with CD274 missense mutations when compared with cases without CD274 mutations, and we also saw significantly lower PD-L1 IHC staining in the clonal missense mutation when compared with the subclonal missense mutations. We hypothesize that this is likely due to the lower rates of PD-L1 antibody binding (from the IHC assay) to the PD-L1 ligand on the tumor cells instead of actual lower PD-L1 protein expression.…”

Pan-cancer landscape ofCD274(PD-L1) copy number changes in 244 584 patient samples and the correlation with PD-L1 protein expression

“…This stands in contrast to genes like ROS1 , where CN changes and ROS1 protein expression detected via IHC are not highly correlated. 27 Instead, CD274 CN gains are more similar to ERBB2 (HER2) CN gains and HER2 protein expression in that they are correlated with each other. 27 Interestingly, HNSCC CD274 CN gains had the highest correlation with PD-L1 IHC positivity.…”

“… 27 Instead, CD274 CN gains are more similar to ERBB2 (HER2) CN gains and HER2 protein expression in that they are correlated with each other. 27 Interestingly, HNSCC CD274 CN gains had the highest correlation with PD-L1 IHC positivity. Furthermore, the highest levels of CN gains were in tumor types with SCC morphology, suggesting that CD274 CN gains could be a particularly useful biomarker for tumors with this morphology.…”

Screening for ROS1 fusions in patients with advanced non-small cell lung carcinomas using the VENTANA ROS1 (SP384) Rabbit Monoclonal Primary Antibody

“…Specificity can reach 100% when stringent interpretation criteria are used (range: 76%-100%) [5, 29,33]. Interestingly, a recent study that compared ROS1 SP384 IHC with NGS also described positive IHC expression in NSCLCs with uncommon ROS1 fusions (SQSTM1), ROS1 mutations and ROS1 amplifications [34].…”

“…Third, significant ROS1 expression (i.e. strong but mostly focal) can be present in ROS1-amplified tumors [34] and in ROS1-non-rearranged tumors containing other oncogenic drivers (mainly EGFR mutations but also KRAS mutations, BRAF mutations, ALK fusions and HER2 abnormalities) [46,52,53,57,[59][60][61]. If the confirmatory method is negative, we should persevere in the search of a therapeutic target using NGS.…”