Evangelist, Makenzi Colleen

e20731 Background: Selective RET (REarranged during Transfection) inhibitors (RETi) have become standard treatment for RET fusion-positive non-small cell lung cancer ( RET + NSCLC), which represent 1–2% of NSCLC cases. Clinical factors that drive front-line versus later-line RETi use and outcomes are not well understood. This retrospective chart review evaluates physician decision drivers alongside real-world effectiveness and safety for pralsetinib (PRAL) in RET + NSCLC. Methods: A retrospective chart review was conducted via a standardized web-based form among US oncologists treating advanced RET + NSCLC. Eligible patients initiated PRAL for RET + NSCLC between October 2020 and December 2024. Data gathered included physician treatment considerations, patient baseline characteristics, and efficacy outcomes. Results: Eighty-two charts from patients who received PRAL as their first (index) RETi were collected from 43 physicians across both academic (41.9%) and community (58.1%) sites. Of the 82 patients, 51.2% received PRAL front line (1L) and 31.7% in the second line (2L). From a predefined list, physicians most often cited comorbidities (36.6%) and ECOG performance status (31.7%) as clinical factors when considering index PRAL therapy and efficacy profile (56.1%), followed by intracranial activity (24.4%) and hypersensitivity to immuno-oncology agents (24.4%) as therapy-related considerations. Although not a primary therapy selection driver, in 13 patients with safety as a consideration, 6 (46.2%) had myelosuppression noted as a concern for index PRAL treatment. RET + NSCLC patients treated in the 1L setting with PRAL had an overall response rate (ORR) of 73.8% (14 CR; 17 PR). For 2L line PRAL, the ORR was 61.5% (1 CR; 15 PR). Anemia (17.1%), diarrhea (13.4%), and constipation (13.4%) were the most frequently reported adverse events (AE). Discontinuation was mainly due to loss of/no response (80.6%), insurance (16.1%), and AEs (3.2%). The single PRAL patient that discontinued due to an AE had edema. There were an additional 7 patients that switched to PRAL due to an AE on a different RETi. The post-switch ORR was 57.1% (4/7); of these patients, 3 maintained their previous response and 1 improved their response. Conclusions: In this retrospective chart review, pralsetinib was used across treatment lines with high real-world response rates, consistent with results from the ARROW trial. Treatment selection was influenced by specific clinical factors including patient comorbidities, ECOG performance status, and safety concerns, with AE-driven switching uncommon yet associated with continued responses.

RET fusions appear in 1%-2% of non–small cell lung cancers (NSCLCs). The results from the ARROW study (ClinicalTrials.gov identifier: NCT03037385 ) supported US Food and Drug Administration approval of pralsetinib, an oral selective RET inhibitor, for metastatic RET -altered NSCLC and RET fusion–positive thyroid cancers. ARROW was a phase I/II open-label study of pralsetinib 400 mg once daily in RET fusion–positive NSCLCs. Coprimary end points were overall response rate (ORR) and safety. Key secondary end points included duration of response, progression-free survival, and overall survival (OS). At data lock (May 20, 2024), 281 patients initiated pralsetinib (median treatment duration, 15.0 months). ORR (measurable disease patients; n = 259) was 78% (95% CI, 69 to 86) for treatment-naïve patients and 63% (95% CI, 54 to 71) for prior platinum-based chemotherapy patients. Median OS was 44.3 months (95% CI, 30.9 to 53.1), 50.1 months (95% CI, 28.3 to not reached) in treatment-naïve patients, and 39.7 months (95% CI, 27.8 to 53.2) in prior platinum patients. Common grade ≥3 treatment-related adverse events were anemia (21%), hypertension (15%), and decreased neutrophils (13%). Three treatment-related deaths occurred (pneumonia, n = 2; interstitial lung disease and rhabdomyolysis, n = 1 each). Safety was consistent with previous ARROW reports; no hypersensitivity was reported in patients receiving prior immunotherapies. Pralsetinib produced robust, durable responses with manageable safety in treatment-naïve and previously treated patients with RET fusion–positive NSCLCs, confirming previous findings with longer follow-up.

8644 Background: RET fusions are targetable oncogenic drivers in 1-2% of non-small cell lung cancers (NSCLC). ARROW (NCT03037385) study results (final data lock May 20, 2024) supported the US FDA approval of pralsetinib, a highly potent, oral, selective RET inhibitor for metastatic RET -altered NSCLC. Here, we present final study results. Methods: ARROW was a phase 1/2 open-label study conducted at 84 sites in 13 countries. Phase 2 included patients with RET -fusion-positive NSCLC who received 400 mg pralsetinib once daily (QD). Initially, treatment-naïve patients were not candidates for platinum-based therapy and presented with several unfavorable prognostic factors; this requirement was removed by protocol amendment in July 2019. Primary objectives were overall response rate (ORR, per RECIST v1.1) and safety. Progression-free survival (PFS) and overall survival (OS) are reported in the full efficacy population; the measurable disease population (MDP) was the primary analysis population for ORR and duration of response (DOR). Results: 281 patients with RET -fusion-positive NSCLC received pralsetinib 400 mg QD, with a median duration of treatment of 14.95 months (mos). Median age was 60 years; 46% were male. In the MDP (n=259), ORR was 70.3% (95% confidence intervals [CI]: 64.3, 75.8) and median DOR was 19.1 mos (95% CI: 14.5, 27.9; Table). In the efficacy population (N=281), median OS was 44.3 mos (95% CI: 30.9, 53.1) with median follow up of 47.6 mos (95% CI: 44.8, 49.2), and median PFS was 13.1 mos (95% CI: 11.4, 16.8). ORR (Table) and median PFS were markedly higher in the US (25.9 mos, n=64) vs. Asia (12.6 mos, n=122) or Europe (12.9 mos, n=95). In the safety population, 95% of patients experienced treatment-related adverse events (TRAEs); 66% experienced ≥grade 3. Common TRAEs included increased AST (n=128 [46%]), anemia (n=121 [43%]), increased ALT (n=98 [35%]), and hypertension (n=77 [27%]). 3 patients died due to TRAEs (pneumonia, n=2; interstitial lung disease and rhabdomyolysis, n=1 each). No new safety signals were identified with this update. Conclusions: Pralsetinib produced clinically meaningful and durable responses in patients with RET -fusion-positive NSCLC (regardless of prior therapies) with a manageable safety profile, confirming with this longer follow up previously published results. Clinical trial information: NCT03037385 . All MDP(n=259) Prior Platinum (n=130) Treatment-naive(n=106) ORR, % (95% CI) Overall 70.3(64.3, 75.8) 63.1(54.2, 71.4) 78.3(69.2, 85.7) US (n=58)77.6(64.7, 87.5) (n=31)64.5(45.4, 80.8) (n=19)100(82.4, 100) Europe (n=89)65.2(54.3, 75) (n=36)63.9(46.2, 79.2) (n=43)65.1(49.1, 79) Asia (n=112)70.5(61.2, 78.8) (n=63)61.9(48.8, 73.9) (n=44)81.8(67.3, 91.8) Median DOR, mos (95% CI) a (n=182)19.1(14.5, 27.9) (n=82)31.8(15.1, 40.4) (n=83)13.4(9.4, 21.7) Median DOR follow up, mos (95% CI) 46.8(42.3, 50.2) 50.3(46.9, 56.8) 42.3(37.4, 44.2) a Per FDA censoring rule.