Amplification of wild-type RET and clinical response to selpercatinib for non-small-cell lung cancer (NSCLC)

9123 Background: RET rearrangements and RET kinase domain mutations represent targetable genomic alterations in various cancer types. However, the frequency and characteristics of RET amplification in cancer and its potential role as a targetable oncogenic driver are not well-characterized. Methods: In a pan-cancer cohort of patients at the Dana-Farber Cancer Institute (DFCI) whose tumors underwent next-generation sequencing (NGS), we evaluated the frequency of wild-type (wt) RET amplification (defined as ≥6 copies) in the absence of RET rearrangements or activating mutations. We validated our findings using merged data from the TCGA, GENIE, and China Pan-Cancer datasets. Results: The frequency of wt RET amplification across all cancers was 0.08% (28/34,463) in the DFCI cohort and 0.16% (145/91,466) in the validation cohort. In NSCLC, the frequency of RET amplification was 0.10% (5/4773) in the DFCI cohort and 0.13% (15/11,622) in the validation cohort. Other cancer types with RET amplification included hepatobiliary cancer, prostate cancer, and breast cancer, among others. For 22 RET-amplified cases with available copy number data , the median RET gene copy number was 7 (range 6-36). Among 20 RET-amplified NSCLCs, 10 had no other known driver mutations, and 10 had concurrent driver mutations (including MET exon 14 skipping, MET amplification, KRAS G12C/S/D, EGFR L858R, EGFR exon 20 insertion, and EGFR exon 19 deletion). In cases with available smoking status, 5 out of 6 patients with RET-amplified NSCLC had a history of tobacco use. A 69-year-old man with unresectable stage III NSCLC had disease recurrence after chemoradiation and durvalumab. Both the initial and recurrent biopsy samples showed focal high-level RET amplification (22 and 28 copies, respectively); genomic and RNA sequencing showed no other driver mutations or RET rearrangements. He experienced partial response to the selective RET inhibitor selpercatinib with decrease of both intracranial and systemic tumor burden. Conclusions: Amplification of wt RET represents a novel, targetable, rare molecular subset of NSCLC and other cancers.