e20610 Background: RET rearrangements have been identified in 1-2% of lung adenocarcinomas. The most common fusion is the KIF5B-RET, the function and roles of the RET fusion oncogene, and its downstream signaling molecules remain unclear. Methods: We constructed a tissue microarray (TMA) comprising 581 resected tumor tissues from lung adenocarcinoma patients and investigated them using FISH with RET break-apart and KIF5B-RET SY translocation probes. NanoString’s nCounter technology was used to assay RETtranscripts. We evaluated the protein expressions of RET and RET-related signaling molecules, including p-AKT and p-ERK, using TMA-based IHC staining. Results: Using FISH, we identified 51 cases (8.8%) of RET variants and 10 cases (1.7%) of KIF5B-RET fusion genes among the 581 cases. RET protein expression was lower in the group harboring KIF5B-RET fusion gene than that in the group harboring a wild type RET gene. We found the activating EGFR mutations in 11 (21.6%) cases of 51 RET variants. For the group with KIF5B-RET fusion gene, the expression of p-ERK was significantly lower in EGFR mutation subgroup with presence of RET protein compared to EGFR mutation subgroup with absence of RET protein. For the group with RET rearrangement, there were significant differences in the expression level of p-AKT (P = 0.028) and, p-ERK protein expression was remarkably increased, especially in cases with no RET protein expression. Conclusions: Taken together, the expression of p-ERK protein was meaningfully increased in the RET variants group regardless of RET protein expression. This result suggests that RET inhibitors combined with ERK inhibitors may be an effective treatment strategy for lung adenocarcinoma patients harboring the RET variants.
Experience with Erlotinib in Lung Adenocarcinoma Harboring a Coexisting KIF5B-RET Fusion Gene and EGFR Mutation: Report of a Rare Case
