Molecular characterisation and clinical outcomes in RET rearranged non-small cell lung cancer (NSCLC).

INTRODUCTION RET rearrangements are an emerging targetable oncogenic fusion driver in NSCLC. However, the natural history of disease and activity of different classes of systemic therapy remain to be defined. Furthermore, molecular testing for RET is not yet routine, and the optimal method of testing is unclear. We present a comparative analysis of molecular profiling with fluorescence in situ hybridization (FISH) or next-generation sequencing (NGS) and treatment outcomes. METHODS This study was a retrospective analysis of patients treated at the National Cancer Centre Singapore. Baseline demographics and treatment outcomes were collected. RESULTS A total of 64 patients were included, with a median age of 62 years (range: 25-85), 56% were women, 77% were of Chinese ethnicity, 95% had adenocarcinoma, and 69% were never smokers. RET rearrangement was detected by FISH in 30 of 34 patients (88%), NGS in 40 of 43 patients (93%), and with discordant results in seven of 13 patients (54%) tested with both methods. Of 61 patients with stage IIIB/IV or recurrent disease, prevalence of central nervous system metastases was 31% and 92% received palliative systemic therapy. Overall survival was prolonged in patients treated with a selective RET tyrosine kinase inhibitor versus untreated patients (median 49.3 versus 15.3 mo; hazard ratio [HR]: 0.16, 95% confidence interval [CI]: 0.06-0.40, p < 0.001). However, it was not different in patients treated with immunotherapy versus untreated patients (median 37.7 versus 49.3 mo; HR: 1.30, 95% CI: 0.53-3.19, p = 0.53). Overall survival was also prolonged in patients with CCDC6-RET fusion versus those with KIF5B-RET fusion (median 113.5 versus 37.7 mo; HR: 0.12, 95% CI: 0.04-0.38, p = 0.009). CONCLUSIONS In RET-rearranged NSCLC, selective RET tyrosine kinase inhibitor therapy is associated with improved survival outcomes, especially in patients with CCDC6-RET fusion. However, immunotherapy has poor efficacy. NGS and FISH testing methods may also result in substantial discordance.