PURPOSE Selpercatinib, a first-in-class, highly selective, and potent CNS-active RET kinase inhibitor, is currently approved for the treatment of patients with RET fusion–positive non–small-cell lung cancer (NSCLC). We provide a registrational data set update in more than double (n = 316) of the original reported population (n = 144) and better characterization of long-term efficacy and safety. METHODS Patients were enrolled to LIBRETTO-001, a phase I/II, single-arm, open-label study of selpercatinib in patients with RET-altered cancers. An analysis of patients with RET fusion–positive NSCLC, including 69 treatment-naive and 247 with prior platinum-based chemotherapy, was performed. The primary end point was objective response rate (ORR; RECIST v1.1, independent review committee). Secondary end points included duration of response (DoR), progression-free survival (PFS), overall survival, and safety. RESULTS In treatment-naive patients, the ORR was 84% (95% CI, 73 to 92); 6% achieved complete responses (CRs). The median DoR was 20.2 months (95% CI, 13.0 to could not be evaluated); 40% of responses were ongoing at the data cutoff (median follow-up of 20.3 months). The median PFS was 22.0 months; 35% of patients were alive and progression-free at the data cutoff (median follow-up of 21.9 months). In platinum-based chemotherapy pretreated patients, the ORR was 61% (95% CI, 55 to 67); 7% achieved CRs. The median DoR was 28.6 months (95% CI, 20.4 to could not be evaluated); 49% of responses were ongoing (median follow-up of 21.2 months). The median PFS was 24.9 months; 38% of patients were alive and progression-free (median follow-up of 24.7 months). Of 26 patients with measurable baseline CNS metastasis by the independent review committee, the intracranial ORR was 85% (95% CI, 65 to 96); 27% were CRs. In the full safety population (n = 796), the median treatment duration was 36.1 months. The safety profile of selpercatinib was consistent with previous reports. CONCLUSION In a large cohort with extended follow-up, selpercatinib continued to demonstrate durable and robust responses, including intracranial activity, in previously treated and treatment-naive patients with RET fusion–positive NSCLC.

Checkpoint inhibitors (CPI) have revolutionized the treatment paradigm for advanced solid tumors; however, there remains an opportunity to improve response rates and outcomes. In preclinical models, 4-1BB costimulation synergizes with CPIs targeting the programmed cell death protein 1 (PD-1)/programmed cell death ligand 1 (PD-L1) axis by activating cytotoxic T-cell–mediated antitumor immunity. DuoBody-PD-L1×4-1BB (GEN1046) is an investigational, first-in-class bispecific immunotherapy agent designed to act on both pathways by combining simultaneous and complementary PD-L1 blockade and conditional 4-1BB stimulation in one molecule. GEN1046 induced T-cell proliferation, cytokine production, and antigen-specific T-cell–mediated cytotoxicity superior to clinically approved PD-(L)1 antibodies in human T-cell cultures and exerted potent antitumor activity in transplantable mouse tumor models. In dose escalation of the ongoing first-in-human study in heavily pretreated patients with advanced refractory solid tumors (NCT03917381), GEN1046 demonstrated pharmacodynamic immune effects in peripheral blood consistent with its mechanism of action, manageable safety, and early clinical activity [disease control rate: 65.6% (40/61)], including patients resistant to prior PD-(L)1 immunotherapy. Significance: DuoBody-PD-L1×4-1BB (GEN1046) is a first-in-class bispecific immunotherapy with a manageable safety profile and encouraging preclinical and early clinical activity. With its ability to confer clinical benefit in tumors typically less sensitive to CPIs, GEN1046 may fill a clinical gap in CPI-relapsed or refractory disease or as a combination therapy with CPIs.

109 Background: RET gene fusions are targetable oncogenic drivers in multiple tumor types, including up to 20% of papillary thyroid cancers (PTC). Pralsetinib is an investigational, highly potent, selective inhibitor of oncogenic RET alterations. In the registration-enabling Phase 1/2 ARROW study (NCT03037385), pralsetinib demonstrated an overall response rate (ORR; response-evaluable patients [REP], central review) of 73% (19/26) in treatment-naïve patients and 61% (49/80; 2 pending confirmation) in platinum-exposed patients with RET fusion+ non-small cell lung cancer (NSCLC) and was well tolerated (data cut-off November 18, 2019). We provide an update on the clinical activity of pralsetinib in other RET fusion+ solid tumor types. Methods: ARROW consists of a phase 1 dose escalation (30–600 mg once [QD] or twice daily) followed by a phase 2 expansion (400 mg QD) in patients with advanced RET-altered solid tumors. Primary objectives were ORR and safety. Results: As of November 18, 2019, 29 patients with metastatic solid tumor types other than NSCLC (16 PTC, 1 undifferentiated thyroid, 3 pancreatic, 3 colon, 6 other) bearing a RET fusion have received pralsetinib. Efficacy data are presented for REP enrolled by July 11, 2019. In patients with thyroid cancer that is RET fusion+, ORR (investigator assessment) was 75% (9/12; all confirmed). Median (range) duration of response (DOR) was 14.5 (3.7+, 16.8) months (mo), with 67% of responding patients continuing treatment. Two patients with stable disease were continuing treatment at 11.5+ and 19.3+ mo. In other RET fusion+ cancers, ORR was 60% (3/5; all confirmed) with partial responses in 2/2 patients with pancreatic cancer (DOR 5.5, 7.4+ mo) and 1 patient with intrahepatic bile duct carcinoma (DOR 7.5 mo). Two patients with colon cancer had stable disease for 7.3 and 9.3 mo. Responses were observed across multiple fusion genotypes. In the entire safety population (all patients treated with 400 mg QD pralsetinib, regardless of diagnosis; n = 354), most treatment-related adverse events (TRAEs) were grade 1-2, and included increased aspartate aminotransferase (31%), anemia (22%), increased alanine aminotransferase (21%), constipation (21%) and hypertension (20%). Only 4% of patients in the safety population discontinued due to TRAEs. Conclusions: Pralsetinib demonstrated broad and durable antitumor activity across multiple advanced solid tumor types, regardless of RET fusion genotype, and was well tolerated. The study is ongoing and still enrolling patients in this cohort. Clinical trial information: NCT03037385.

9065 Background: Selpercatinib, a first-in-class highly selective and potent, CNS-active RET kinase inhibitor, is approved in multiple countries for treatment of RET fusion+ lung or thyroid cancers. Here we report an update of efficacy and safety results which provide a longer follow up and increased number of patients (safety population: N = 345 vs N = 329). Methods: Pts with RET fusion+ NSCLC enrolled in the global, multicenter, ongoing LIBRETTO-001 trial (NCT03157128; 16 countries, 89 sites) were included in this analysis. Pts with the opportunity to be followed ≥6 months from their first dose were included in the efficacy-evaluable population for these analyses. Integrated analysis set (IAS) included 218 NSCLC pts with prior platinum-chemotherapy. Primary analysis set (PAS) was a subset of the IAS and included the first 105 consecutively enrolled pts. The treatment-naïve population included 48 efficacy-evaluable pts. Primary endpoint was objective response rate (ORR, RECIST v1.1) by independent review committee (IRC). Secondary endpoints included ORR by investigator, duration of response (DoR), progression-free survival (PFS), clinical benefit rate (CBR; CR+PR+SD ≥16 weeks), and safety. Safety population (N = 345) included all pts with NSCLC who received ≥1 selpercatinib dose by data cutoff (30 Mar 2020). Results: In pts with prior treatment (N = 218) and treatment-naïve (N = 48) pts, 56% and 60% were female, with a median pt age of 61 and 64 years, respectively. The ORR with selpercatinib was 57% in the IAS, 64% in the PAS, and 85% in the treatment-naïve population (Table). In both the IAS and PAS, the median DoR was 17.5 months, median PFS was 19.3 months at median follow-up of 12.0 and 15.7 months, respectively (Table). The most common treatment-emergent adverse events (TEAEs) reported in ≥25% of pts were dry mouth, diarrhea, hypertension, increased ALT/AST, edema peripheral, and fatigue. Twenty-five pts (7%) permanently discontinued due to TEAEs, with 10 pts (3%) discontinuing selpercatinib due to treatment-related AEs as per investigator. Conclusions: In this updated data set, selpercatinib continued to demonstrate durable antitumor activity in pts with RET-fusion+ NSCLC. Selpercatinib was well-tolerated with a safety profile consistent with previous reports. A global, randomized, phase 3 trial (LIBRETTO-431) evaluating selpercatinib compared with standard frontline therapy is ongoing. Clinical trial information: NCT03157128. [Table: see text]

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