Fluorescent In Situ Hybridization Testing Allows the Diagnosis of NRG1 Gene Fusions in Lung and Pancreas Cancers with No Other Identified Oncogenic Driver

Abstract

Some pancreatic ductal-type (PDADK) and lung adenocarcinomas (LADK) lacking other molecular drivers are reported to harbor NRG1 fusions as potential novel therapeutic targets. We investigated the feasibility of a fluorescent in situ hybridization (FISH)-based diagnosis of NRG1 fusions in a case series of PDADK and LADK lacking other identified oncogenic drivers. First, among a case series of PDADK, KRAS analyses (PCR followed in PCR-negative cases by RNA sequencing-RNAseq) found 27/162 (16.7%) KRAS wild-type cases, among which 1/162 (0.6%) NRG1 fusion was diagnosed using FISH. Secondly, among a case series of LDAK, 191/446 (42.8%) cases had no molecular alterations in EGFR, KRAS, BRAF, HER2, MET, ALK, ROS1 and RET according to NGS and FISH analyses and, among them, 4/446 (0.9%) cases had NRG1 fusions using FISH. Finally, four additional cases out of the two previously mentioned cases series (1 PDADK and 3 LADK) with NRG1 fusions diagnosed by first-line RNAseq were also concluded as NRG1 FISH-positive. The NRG1 FISH tests for the nine NRG1 FISH-positive cases resulted in 50% to 80% of positive tumor nuclei, all with single 3'-NRG1 FISH signals. In our series, of the 22 cases analyzed with both NRG1 FISH (positivity criterion of at least 15% of tumor nuclei with a split between the 5'- and the 3'- parts of the probes and/or isolated single 3'-NRG1 signal) and RNAseq, 17 cases were FISH- RNAseq- and 5 cases were FISH+ RNAseq+ (no FISH+ RNAseq- or FISH- RNAseq+ cases in our study) resulting in 100% sensibility and specificity for the NRG1 FISH test. In the case of no access to RNAseq, NRG1 FISH consists of a valuable tool searching for NRG1 fusions in patients with advanced cancers.

Keywords: NRG1 fusion; RNA-sequencing; fluorescent in situ hybridization; lung cancer; pancreatic cancer.

Figure 1

Histopathological and NRG1 fluorescent in situ hybridization (FISH) images of tumors with NRG1 fusions (Lung #1: (A,B); Lung #2: (C,D); Lung #3: (E,F); Lung #4: (G,H); Pancreas #1: (I,J); example of NRG1 FISH-negative result in a RNAseq negative pancreatic tumor: (K); (A,C,E,G,I): hematoxylin eosin saffron, ×20 magnification; (B,D,F,H,J,K): ZytoLight SPEC NRG1 Dual Color Break Apart probe, DAPI counterstaining, ×100 magnification).