Mehren, Margaret von

TPS11579 Background: Gastrointestinal stromal tumors (GIST) are commonly driven by mutations in the receptor tyrosine kinase KIT . Resistance to approved tyrosine kinase inhibitors (TKIs) arises from additional KIT mutations in the ATP-binding pocket (AP) and activation loop (AL). No single approved TKI broadly suppresses all resistant clones, and overlapping VEGFR inhibition and toxicity limits TKI combinations. The type I TKI bezuclastinib (“BEZ,” CGT9486) inhibits KIT AL resistance mutations, does not inhibit VEGFR, and has complimentary activity with sunitinib (“SUN,” inhibitor of KIT AP resistance mutations). The first-in-human study (PLX121-01) and ongoing Peak trial (NCT05208047) evaluated BEZ+SUN showing promising safety and efficacy in GIST. SARC044 investigates BEZ+SUN in patients (pts) with SUN-resistant, KIT-mutant GIST, and correlatives aim to determine mechanisms of response and resistance (NCT06208748). Methods: SARC044 is a multi-center, open label, single-arm phase II trial enrolling up to 40 adult pts with KIT exon 9 or 11-mutant GIST resistant to imatinib and SUN. After TKI washout (baseline, “b/l”), pts initiate BEZ 600 mg daily for 2 weeks, then add SUN 37.5 mg daily, taking both drugs continuously (28-day cycles) until mRECISTv1.1 progression or unmanageable toxicity. Response evaluations (RE) are performed every 8 weeks (wk) through 15 months (mo) on study, then every 12 wk. Circulating tumor DNA (ctDNA) is collected at b/l, cycle 1 day 15 (C1D15), C2D1, C3D1, and progression. Targeted exome sequencing (TES) of ctDNA will track primary/resistant KIT mutation dynamics across therapy. 18 FDG PET/CTs are performed in 20 pts at b/l, C1D15, and C2D1, which guide a biopsy of a resistant tumor. TES, allele-specific and long-read PCR (to detect AP+AL mutation phasing), and immunoblotting (evaluating KIT pathway activation) will be performed on tissue. EORTC QLQ-C30 surveys collect pt-reported outcomes (PRO) at b/l, on treatment, and at progression. The primary endpoint is median progression-free survival (mPFS) and secondary endpoints include overall survival at 1 and 2 years, clinical benefit rate at 16 wk, adverse event rate, PRO, and KIT mutation profile in ctDNA and tissue. 35 evaluable pts achieves 83% power (p<0.05, one-sided) in a one-sample log-rank test to detect a mPFS of 6.5 mo vs 4 mo (historic control). Expected accrual is 12 mo across 4 sites in the United States with ~36 mo to study completion. Clinical trial information: NCT06208748 .

In the INTRIGUE phase III trial (ClinicalTrials.gov identifier: NCT03673501 ), adult patients with advanced gastrointestinal stromal tumor previously treated with imatinib were randomly assigned 1:1 to ripretinib 150 mg once daily or sunitinib 50 mg once daily (4 weeks on/2 weeks off). In the primary analysis, overall survival (OS) was immature. In this study, we report the final planned analysis of OS (key secondary end point), progression-free survival (PFS) on third-line therapy (second PFS; prespecified exploratory end point), and long-term safety. Final OS analysis was prespecified to occur with approximately 200 and ≥145 events in the overall and KIT exon 11 intention-to-treat (ITT) populations, respectively. As of March 15, 2023, there were 211 and 151 OS events in the overall ITT and KIT exon 11 ITT populations, respectively. Median OS was similar between second-line ripretinib and sunitinib in both populations (overall, 35.5 v 31.5 months; KIT exon 11, 35.5 v 32.8 months). Median second PFS (on third-line therapy) for the overall ITT population was similar between the ripretinib and sunitinib arms (7.7 v 7.4 months). Safety was consistent with the primary analysis. OS from this analysis was similar between arms, and second PFS suggests that receiving ripretinib did not adversely affect the PFS of third-line therapy.

826 Background: After initial response to first line therapy with imatinib, GISTs commonly progress due to secondary resistance mutations in KIT. As the KIT mutation targeting profiles of bezuclastinib (type I TKI) and sunitinib are distinct, when combined they inhibit a broad spectrum of secondary KIT mutations. Herein we report extended experience of patients treated with 2 nd line combination bezuclastinib and sunitinib, including response assessment and safety. Methods: Peak (NCT05208047), a global randomized Phase 3, open-label study, aims to evaluate efficacy and safety of bezuclastinib + sunitinib vs sunitinib in GIST pts with imatinib intolerance or resistance. In Part 1a of the 3-part study, the dose of an optimized formulation of bezuclastinib was escalated in serial cohorts to achieve a target exposure comparable to that achieved at the RP2D established in the prior Phase 1b/2a study. Part 1b evaluated the interaction between bezuclastinib + sunitinib. Key inclusion: adult with locally advanced, metastatic and/or unresectable GIST, ≥1 measurable lesion according to modified RECIST v1.1, and ECOG PS 0 to 2. Part 1 completed enrollment in Apr 2023. Based upon PK and safety, a dose of bezuclastinib 600 mg QD + sunitinib 37.5 mg QD was selected for Part 2. All Part 1 data reported herein are as of Aug 2023; updated safety and efficacy will be presented. Results: Part 1 has completed enrollment with 19 pts in Part 1a and 23 in 1b. In Part 1a, Cohort 1 included 5 pts starting at bezuclastinib 300 mg QD + sunitinib 37.5 mg QD; Cohort 2 included 14 pts at bezuclastinib 600 mg QD + sunitinib 37.5 mg QD. Pt characteristics in Part 1a+1b: median age - 60 yrs (range: 33-77); 81% men; 98% ECOG PS 0-1; 98% metastatic and 2% locally advanced. The majority of TEAEs were low grade and reversible with low rate (38%) of Grade 3+ events. There were limited (24%) dose reductions and infrequent (n=2) discontinuations due to TEAEs. Three pts experienced serious AEs possibly associated with study medications. In pts evaluable for response (received ≥1 cycle of study treatment and had assessments at baseline and post-baseline [n=40]), the objective response rate (ORR) was 20% (6 confirmed PRs, 2 unconfirmed PRs). Data remain immature to estimate median PFS for Part 1 pts. In a subset of pts with prior imatinib only (n=6), the closest approximation for pts enrolling in Part 2, the ORR was 33% (2 confirmed PRs). The majority of 2nd-line pts remain on treatment past 12 months. Conclusions: Data from Peak Part 1 show an encouraging safety and tolerability profile generally consistent with published sunitinib monotherapy experience. ORR in evaluable pts from Part 1 was 20%; ORR in 2 nd line pts was 33%. Part 2 of the Peak study is actively enrolling pts globally at the selected dose of bezuclastinib 600 mg QD + sunitinib 37.5 mg QD versus sunitinib 37.5 mg QD. Clinical trial information: NCT05208047 .

11533 Background: After initial response to first line therapy with imatinib, GISTs commonly progress due to secondary resistance mutations in KIT. As the KIT mutation targeting profiles of bezuclastinib (type I TKI) and sunitinib are distinct, when combined they inhibit a broad spectrum of secondary KIT mutations. Herein we report extended experience of patients treated with 2nd line combination bezuclastinib and sunitinib, including response assessment and safety. Methods: Peak (NCT05208047), a global randomized Phase 3, open-label study, aims to evaluate efficacy and safety of bezuclastinib + sunitinib vs sunitinib in GIST pts with imatinib intolerance or resistance. In Part 1a of the 3-part study, the dose of an optimized formulation of bezuclastinib was escalated in serial cohorts to achieve a target exposure comparable to that achieved at the RP2D established in the prior Phase 1b/2a study. Part 1b evaluated the interaction between bezuclastinib + sunitinib. Key inclusion: adult with locally advanced, metastatic and/or unresectable GIST, ≥1 measurable lesion according to modified RECIST v1.1, and ECOG PS 0 to 2. Part 1 completed enrollment in Apr 2023. Based upon PK and safety, a dose of bezuclastinib 600 mg QD + sunitinib 37.5 mg QD was selected for Part 2. All Part 1 data reported herein are as of Aug 2023; updated safety and efficacy will be presented. Results: Part 1 has completed enrollment with 19 pts in Part 1a and 23 in 1b. In Part 1a, Cohort 1 included 5 pts starting at bezuclastinib 300 mg QD + sunitinib 37.5 mg QD; Cohort 2 included 14 pts at bezuclastinib 600 mg QD + sunitinib 37.5 mg QD. Pt characteristics in Part 1a+1b: median age - 60 yrs (range: 33-77); 81% men; 98% ECOG PS 0-1; 98% metastatic and 2% locally advanced. The majority of TEAEs were low grade and reversible with low rate (38%) of Grade 3+ events. There were limited (24%) dose reductions and infrequent (n=2) discontinuations due to TEAEs. Three pts experienced serious AEs possibly associated with study medications. In pts evaluable for response (received ≥1 cycle of study treatment and had assessments at baseline and post-baseline [n=40]), the objective response rate (ORR) was 20% (6 confirmed PRs, 2 unconfirmed PRs). Data remain immature to estimate median PFS for Part 1 pts. In a subset of pts with prior imatinib only (n=6), the closest approximation for pts enrolling in Part 2, the ORR was 33% (2 confirmed PRs). The majority of 2nd-line pts remain on treatment past 12 months. Conclusions: Data from Peak Part 1 show an encouraging safety and tolerability profile generally consistent with published sunitinib monotherapy experience. ORR in evaluable pts from Part 1 was 20%; ORR in 2nd line pts was 33%. Part 2 of the Peak study is actively enrolling pts globally at the selected dose of bezuclastinib 600 mg QD + sunitinib 37.5 mg QD versus sunitinib 37.5 mg QD. Clinical trial information: NCT05208047 .

Abstract Purpose: Epithelioid hemangioendothelioma (EHE) is a rare vascular cancer with pathogenic TAZ–CAMTA1 (calmodulinbinding transcription activator 1) operating as an oncogenic driver through activation of the MAPK pathway. Trametinib is an inhibitor of MEK, a critical kinase in the MAPK pathway. We sought to evaluate the effect of trametinib in patients with EHE. Patients and Methods: A phase 2 trial of trametinib was conducted in patients with locally advanced or metastatic EHE. Eligibility requirements included evidence of tumor progression or presence of EHE-related pain requiring opiates for management before enrollment. The primary endpoint was objective response rate (ORR) as per RECIST1.1 in cases with TAZ– CAMTA1 confirmed by fusion-FISH. Secondary objectives were to estimate ORR for all patients, median progression-free survival (PFS), 2-year overall survival (OS) rate, patient safety, and change in patient-reported global health and pain scores per PROMIS questionnaires. Results: 44 patients enrolled and 42 started trametinib. TAZ– CAMTA1 was detected in 27 tumor samples. TheORRwas 3.7%[95% confidence interval (CI), 0.094–19.0], median PFS was 10.4 months (95%CI, 7.1–NA), and 2-year OS rate was 33.3%(95%CI, 19.1–58.2) in the target population. Median pain intensity and interference scores improved significantly after 4 weeks of trametinib in patients using opiates. Common adverse events related to trametinib were rash, fatigue, nausea/vomiting, diarrhea/constipation, alopecia, and edema; one grade 5 ARDS/pneumonitis was related to trametinib. Conclusions: Trametinib was associated with reduction in EHE-related pain and median PFS of more than 6 months, providing palliative benefit in patients with advanced EHE, but the trial did not meet the ORR goal. See related commentary by Van Tine and Haarberg, p. 4552

748 Background: Ripretinib is a switch-control tyrosine kinase inhibitor approved for patients (pts) with gastrointestinal stromal tumor (GIST) who received prior treatment with 3 or more kinase inhibitors, including imatinib. Sunitinib is approved for advanced GIST after imatinib failure. In the second interim analysis of overall survival (OS) from the phase 3 INTRIGUE study, the OS event rate was 41% in the all-patient (AP) intent-to-treat (ITT) population, and OS was similar between treatment arms in both the KIT exon 11 ITT and AP ITT populations. Here, we present the final OS and updated safety from INTRIGUE. Methods: INTRIGUE (NCT03673501) is an open-label, phase 3 study of adults with advanced GIST who had disease progression on or intolerance to imatinib. Randomization was 1:1 to ripretinib 150 mg once daily (QD) or sunitinib 50 mg QD (4 weeks on/2 weeks off) and was stratified by KIT mutational status and imatinib intolerance. OS was a key secondary endpoint (the primary endpoint of progression-free survival was reported previously); final OS analysis was prespecified to occur with ≥200 and ≥145 events in the AP ITT and KIT exon 11 ITT populations, respectively. Data cutoff was March 15, 2023. Results: Of 453 pts, 444 received treatment; 40 remain on treatment (ripretinib, 28/223 [13%]; sunitinib, 12/221 [5%]). Treatment discontinuation was due to progressive disease (PD) by independent radiologic review (56%), PD by investigator (11%), clinical PD (6%), withdrawal of consent (6%), and adverse events (AEs; 5%). Fewer pts discontinued treatment due to AEs with ripretinib vs sunitinib (3% vs 6%). There were 211 OS events (47%) in the AP ITT population and 151 OS events (46%) in the KIT exon 11 ITT population. OS was similar with ripretinib vs sunitinib in the 2 ITT populations (Table). Fewer pts had grade 3/4 treatment-emergent AEs with ripretinib vs sunitinib (43% vs 67%). Dose interruptions and reductions were lower with ripretinib vs sunitinib. Median treatment duration for ripretinib vs sunitinib was 7.9 vs 6.5 months. Conclusions: In the finalOS analysis from the INTRIGUE study, OS was similar between treatment arms. The safety profile remained consistent and more favorable for ripretinib vs sunitinib in pts with advanced GIST previously treated with imatinib. Clinical trial information: NCT03673501 . [Table: see text]

This selection from the NCCN Guidelines for Adolescent and Young Adult (AYA) Oncology focuses on considerations for the comprehensive care of AYA patients with cancer. Compared with older adults with cancer, AYA patients have unique needs regarding treatment, fertility counseling, psychosocial and behavioral issues, and supportive care services. The complete version of the NCCN Guidelines for Adolescent and Young Adult (AYA) Oncology addresses additional aspects of caring for AYA patients, including risk factors, screening, diagnosis, and survivorship.

e23508 Background: Activating mutations in KIT are found in most pts with GIST. First-line imatinib provides initial clinical benefit in advanced disease, but prognosis is poor for pts whose tumors progress, despite 3 other approved tyrosine kinase inhibitors (TKIs). Resistance is typically driven by secondary KIT mutations in the ATP-binding pocket (exons 13/14) or activation loop (exons 17/18). No approved drug has potent activity against both classes of resistance mutations, and many pts have polyclonal resistance after multiple lines of therapy. THE-630 is an investigational pan-variant KIT inhibitor. Based on preclinical models, an average plasma concentration (Cav) of 100 nM is predicted to have potent activity against all major classes of KIT-activating and resistance mutations. Here, we report initial data from a first-in-human study in pts with advanced GIST (NCT05160168). Methods: This ph 1/2 study is assessing the safety (including dose-limiting toxicities [DLTs] and recommended ph 2 dose [RP2D]), pharmacokinetics (PK), and antitumor activity of THE-630. Pts enrolled in the ph 1 portion were ≥18 y, had unresectable or metastatic GIST previously treated with imatinib and ≥1 additional TKI, and had ECOG performance status ≤2. Pts received THE-630 (QD; 28-day cycles) in a 3+3 dose-escalation design. PK was assessed on days 1 and 15 in cycle 1, antitumor activity was assessed by modified RECIST 1.1, and circulating tumor DNA (ctDNA) was assessed using Guardant360. Results: As of 13 Jan 2023, 19 pts had been treated in the ph 1 portion at THE-630 daily doses of 3 mg (n = 3), 4 mg (n = 7), 6 mg (n = 3), 9 mg (n = 3), and 12 mg (n = 3). Median age was 57 y (range 39–72); 13 pts had ≥4 prior TKIs. Median treatment duration was 55 days (range 1–252). PK analysis shows approximately dose-proportional increase in systemic exposure across doses tested. Mean steady-state Cav at 12 mg was 47 nM. There was 1 DLT at 4 mg (grade 5 myocardial infarction in a pt with 8 prior TKIs and hyperlipidemia where relationship to THE-630 could not be incontrovertibly ruled out). No other DLTs or related serious adverse events have occurred; 13 pts had treatment-related AEs (TRAEs), 91% of which were grade 1–2. The most common TRAEs were fatigue (n = 4), dry mouth (n = 3), anemia, ALT increase, AST increase, diarrhea, dyspepsia, dyspnea, and hypertension (n = 2 each). Reductions in select KIT-mutant allele fractions in ctDNA were observed, consistent with THE-630 levels achieved thus far. Stable disease (SD) was the best response in 1/7 pts at 4 mg, 1/3 pts at 6 mg, and 3/3 pts at 9 mg. Post data cut, SD was seen in 3/3 pts at 12 mg. Dose escalation continues to determine the RP2D. Conclusions: THE-630 had an acceptable initial safety profile, and escalation continues, as target exposure for pan-variant KIT activity is not yet reached. Reduction in KIT-mutant allele fractions in ctDNA and initial evidence of disease control were observed. Clinical trial information: NCT05160168 .

11536 Background: Ripretinib is a switch-control tyrosine kinase inhibitor approved for patients (pts) with gastrointestinal stromal tumor (GIST) who received prior treatment with ≥3 kinase inhibitors, including imatinib. Exploratory baseline circulating tumor DNA (ctDNA) next-generation sequencing (NGS) analysis from INTRIGUE showed pts with second-line advanced GIST with primary KIT exon 11 mutations and secondary resistance mutations exclusively in KIT exons 17/18 derived clinical benefit from ripretinib but not sunitinib (Bauer S et al. J Clin Oncol. 2023; Abs 397784). Outcomes in pts with advanced GIST with ctDNA not detected (ctDNA-ND) had not been evaluated. Here, we present exploratory data from INTRIGUE in pts who had baseline ctDNA-ND vs ctDNA detected (ctDNA-D). Methods: INTRIGUE is an open-label, phase 3 study that enrolled pts with advanced GIST who had disease progression on or intolerance to imatinib (NCT03673501). Pts were randomized 1:1 to ripretinib 150 mg once daily (QD) or sunitinib 50 mg QD (4 wks on/2 wks off) and stratified by mutation according to local pathology report. Baseline peripheral whole blood was analyzed by Guardant360, a 74-gene ctDNA NGS-based assay. Pts with ctDNA-D had ≥1 somatic alteration in the 74 genes analyzed. Results: Pts with ctDNA-ND (82/362, 22.7%) were younger (median: 55.5 vs 62.0 years) and had smaller sums of longest diameters of target lesions (median [range]: 57.6 [11–459] vs 108.8 [15–418] mm) vs ctDNA-D (280/362, 77.3%). Progression-free survival (PFS) was longer in pts with ctDNA-ND vs ctDNA-D and numerically higher with ripretinib vs sunitinib in pts with ctDNA-ND (Table). Pts with ctDNA-ND categorized as not having a KIT exon 9 mutation at randomization ( KIT exon 11, other KIT/PDGFRA, or KIT/PDGFRA wild-type; n = 71) had longer PFS with ripretinib vs sunitinib (median not estimable [NE] vs 11 months; HR = 0.56; 95% CI 0.28 to 1.12). Objective response rate (ORR) and overall survival (OS) were higher with ctDNA-ND vs ctDNA-D. Safety was similar between groups and consistent with the primary analysis. Conclusions: Pts with ctDNA-ND had better efficacy outcomes vs pts with ctDNA-D in both treatment arms; PFS was numerically higher with ripretinib vs sunitinib in pts with ctDNA-ND. Although little is known about the biology driving ctDNA in GIST, these data suggest pts may have improved outcomes and different treatment sensitivity based on ctDNA detectability. Clinical trial information: NCT03673501 . [Table: see text]

11524 Background: Ripretinib is a switch-control tyrosine kinase inhibitor approved for patients (pts) with gastrointestinal stromal tumor (GIST) who received prior treatment with ≥3 kinase inhibitors, including imatinib. Sunitinib is approved for advanced GIST after imatinib failure. In the first interim analysis (IA) for overall survival (OS) in the INTRIGUE trial, data were immature (OS event rate, 22.3%), and median OS was not reached in either arm for the KIT exon 11 intent-to-treat (ITT) and all-patient (AP) ITT populations (S Bauer, et al. J Clin Oncol. 2022). Additionally, ripretinib had a more favorable safety profile with fewer grade 3/4 treatment-emergent adverse events (TEAEs) than sunitinib. Here, we present the second IA of OS and updated safety from INTRIGUE. Methods: INTRIGUE is a global, open-label, phase 3 study that enrolled adult pts with advanced GIST who had disease progression on or intolerance to imatinib (NCT03673501). Randomization was 1:1 to ripretinib 150 mg once daily (QD) or sunitinib 50 mg QD (4 wks on/2 wks off) and was stratified by KIT mutational status and imatinib intolerance. OS was a key secondary endpoint; data cutoff for the second IA was Sept 1, 2022. Results: Of 453 pts in the AP ITT population, 444 received treatment; 51 remain on treatment (33/223 [14.8%] with ripretinib and 18/221 [8.1%] with sunitinib). Common reasons for treatment discontinuation were progressive disease (PD) assessed by independent radiologic review (55.4%), PD assessed by investigator (10.6%), clinical PD (5.9%), withdrawal of consent (5.4%), and adverse event (AE; 4.5%); fewer pts discontinued due to an AE for ripretinib vs sunitinib (2.7% vs 6.3%). Following study treatment discontinuation, 58 pts (25.6%) from the sunitinib arm received ripretinib; 139 pts (61.5%) from the ripretinib arm later received sunitinib. There were 185 OS events (40.8%) in the AP ITT population; median duration of follow-up was 28.7 and 28.5 months for ripretinib and sunitinib, respectively. OS was similar with ripretinib vs sunitinib in the AP ITT (median 35.5 vs 30.9 months; HR 0.88, 95% CI 0.66 to 1.18; nominal P = 0.39) and KIT exon 11 ITT populations (median 34.0 vs 31.5 months; HR 1.05, 95% CI 0.75 to 1.48; nominal P = 0.77). The updated safety profile was consistent with the primary analysis; fewer pts had grade 3/4 TEAEs with ripretinib vs sunitinib (95 [42.6%] vs 149 [67.4%]). Dose interruptions and reductions were lower with ripretinib vs sunitinib. The median (range) treatment duration was 7.9 (0.2–38.2) months for ripretinib and 6.5 (0.2–38.3) months for sunitinib. Conclusions: In the second IA from INTRIGUE, OS was similar between treatment arms. The safety profile remained consistent with additional data, and results demonstrate favorable safety with ripretinib in pts with advanced GIST previously treated with imatinib. Clinical trial information: NCT03673501 .