Chung, Hyun Cheol

TPS371 Background: Tucatinib (TUC), a highly selective HER2-directed tyrosine kinase inhibitor (TKI) approved in multiple regions for HER2+ metastatic breast cancer, is being developed as a novel therapy for patients (pts) with GI tumors including gastric or gastroesophageal junction adenocarcinoma (GEC). While trastuzumab (Tras) with chemotherapy is standard in the 1st-line setting for metastatic HER2+ GEC, no anti-HER2 therapy has demonstrated an OS benefit over chemotherapy as 2nd-line therapy, possibly due to loss of HER2 expression following Tras-based therapy. In GEC xenograft models, dual targeting of HER2 with TUC and Tras showed superior activity to either agent alone.(Kulukian 2020) Interim results from the MOUNTAINEER study have shown promising activity for TUC and Tras for HER2+ mCRC.(Strickler 2019) The MOUNTAINEER-02 study is evaluating the efficacy and safety of TUC with Tras, ramucirumab (Ram), and paclitaxel (Pac) in pts with HER2+ GEC in the 2nd-line setting. Methods: MOUNTAINEER-02 (NCT04499924) is a phase 2/3 study evaluating TUC + Tras with Ram and Pac. Pts receive TUC 300 mg or placebo PO BID, Tras (6 then 4 mg/kg) or placebo (IV on Days 1 and 15 of each 28-day cycle), Pac (IV on Days 1, 8, 15), and Ram (IV on Days 1 and 15). Eligible pts have locally-advanced unresectable or metastatic HER2+ GEC and have received a HER2-directed antibody and 1 prior line of therapy for advanced disease. Pts must be ≥18 years of age, with an ECOG ≤1, and have had no prior exposure to Ram, anti-HER2 or anti-EGFR TKI, HER2-directed antibody-drug conjugates, or taxanes ≤12 months before enrollment. Due to the potential impact of TUC on Pac metabolism, the study will include an initial Pac dose optimization stage. The open-label phase 2 part will determine the recommended dose of Pac (60 or 80 mg/m²) combined with TUC, Tras, and Ram in 6-18 pts, and evaluate safety and activity of the regimen in Cohorts 2A and 2B (30 pts each). The randomized, double-blind, phase 3 part will compare the efficacy and safety of TUC and Tras (Arm 3A; ̃235 pts) vs. placebo (Arm 3B; ̃235 pts), both in combination with Ram and Pac, and also evaluate activity of TUC with Ram and Pac (Arm 3C; ̃30 pts). The dual primary phase 3 endpoints are OS and PFS per investigator, with confirmed ORR as a key secondary endpoint. HER2 status is determined at baseline using a blood-based NGS assay, and IHC/ISH of fresh or archival tumor biopsies, if available. Pts must be HER2+ by blood-based NGS in Cohort 2A and phase 3; in Cohort 2B, pts must be HER2+ in a biopsy taken post-progression during/after 1st-line therapy, but HER2-negative by blood-based NGS. Disease assessments per RECISTv1.1 will occur q6 weeks for 36 weeks, then q9 weeks. The pharmacokinetics of TUC, Pac, and their metabolites will be evaluated in a subset of pts, including a cohort with gastrectomies. Enrollment in phase 2 is ongoing. Clinical trial information: NCT04499924.

TPS264 Background: Trastuzumab (T), a monoclonal antibody (mAb) targeting HER2, is standard of care 1st-line therapy for advanced HER2+ GEJ/GC patients. M, an investigational Fc-engineered anti-HER2 mAb, targets the same HER2 epitope but with higher affinity for both 158V (high binding) and 158F (low binding) alleles of activating Fc receptor CD16A. Data suggest margetuximab coordinately enhances both innate and adaptive immunity, including antigen-specific T-cell responses to HER2. PD-1 and LAG-3 are T-cell checkpoint molecules that suppress T-cell function. Retifanlimab (also known as MGA012 or INCMGA00012) is a humanized, hinge-stabilized, IgG4 Κ anti-PD-1 mAb blocking binding of PD-L1 or PD-L2 to PD-1. Tebotelimab (also known as MGD013) is a humanized Fc-bearing bispecific tetravalent DART® protein that binds to both PD-1 and LAG-3, inhibiting their respective ligand binding. We previously reported that a CTX-free regimen of M+PD-1 blockade was well tolerated in GEJ/GC patients, and induced a 44% objective response rate (ORR) in a double-positive biomarker population. This was 2- to 3-fold greater than in historical controls with checkpoint inhibitors alone. This registration-directed trial assesses efficacy, safety, and tolerability of M+checkpoint inhibition ± CTX in metastatic/locally advanced, treatment-naïve, HER2+ GEJ/GC patients. Methods: This is a 2-cohort, adaptive open-label phase 2/3 study (NCT04082364). The first single arm, CTX-free cohort A, evaluates M+retifanlimab in HER2+ (immunohistochemistry [IHC] 3+) and PD-L1+ (excluding microsatellite instability high) patients. After 40 patients are evaluated for response/safety, additional patients will be enrolled if the threshold for continuation is met. In randomized cohort B, HER2+ (IHC 3+ or 2+/fluorescent in situ hybridization+) patients are enrolled irrespective of PD-L1 status. Part 1 of cohort B randomizes patients to 1 of 4 arms (50 patients each): control arm (T+CTX) or 1 of 3 experimental arms (M+CTX; M+CTX+retifanlimab; M+CTX+tebotelimab). CTX is investigator’s choice XELOX or mFOLFOX-6. Part 2 of cohort B consists of control (T+CTX) vs 1 experimental arm (M+CTX) + either retifanlimab or tebotelimab, depending on results from part 1; with 250 patients each. The primary efficacy endpoint for cohort A (both parts) is ORR per RECIST 1.1; for cohort B part 2 it is overall survival. Clinical trial information: NCT04082364.

TPS252 Background: Tucatinib (TUC), a highly selective HER2-directed TKI recently approved for HER2+ metastatic breast cancer (MBC), is being developed as a novel therapy for patients (pts) with metastatic colorectal cancer (mCRC) and other GI tumors. While trastuzumab (Tras) with chemotherapy is standard in the 1st-line setting for metastatic HER2+ gastric or gastroesophageal junction adenocarcinoma (GEC), no anti-HER2 therapy has demonstrated an OS benefit over chemotherapy in 2nd-line, possibly due to loss of HER2 expression following Tras-based therapy. In GEC xenograft models, dual targeting of HER2 with TUC and Tras showed superior activity to either agent alone. Interim results from the MOUNTAINEER study have shown promising activity for TUC and Tras in HER2+ mCRC. The MOUNTAINEER-02 study is evaluating the efficacy and safety of TUC in combination with Tras, ramucirumab (Ram), and paclitaxel (Pac) in pts with HER2+ GEC. Methods: MOUNTAINEER-02 (NCT04499924) is a phase 2/3 study evaluating TUC and Tras with the 2nd-line standard of care, Ram and Pac. Pts receive TUC 300 mg or placebo PO BID, Tras (6 then 4 mg/kg) or placebo (IV on Days 1 and 15 of each 28-day cycle), Pac (IV on Days 1, 8, 15), and Ram (IV on Days 1 and 15). Eligible pts have locally-advanced unresectable or metastatic HER2+ GEC, have received a HER2-directed antibody, and 1 prior line of therapy for advanced disease. Pts must be ≥18 years of age, with an ECOG ≤1, and have had no prior exposure to Ram, anti-HER2 or anti-EGFR TKI, HER2-directed antibody-drug conjugates, or taxanes ≤12 months before enrollment. Due to the potential impact of TUC on Pac metabolism, the study will include an initial Pac dose finding stage. The open-label phase 2 part will determine the recommended dose of Pac (60 or 80 mg/m²) combined with TUC, Tras, and Ram in 6-12 patients, and evaluate the safety and activity of the regimen in Cohorts 2A and 2B (30 patients each). The randomized, double-blind, phase 3 part will compare the efficacy and safety of TUC and Tras (Arm 3A; ~235 patients) vs. placebo (Arm 3B; ~235 patients), both in combination with Ram and Pac, and also evaluate activity of TUC with Ram and Pac (Arm 3C; ~30 patients). The dual primary phase 3 endpoints are OS and PFS per investigator, with confirmed ORR as a key secondary endpoint. HER2 status is determined at baseline using a blood-based NGS assay, and IHC/ISH of fresh or archival tumor biopsies, if available. Pts must be HER2+ by blood-based NGS in Cohort 2A and phase 3; in Cohort 2B, pts must be HER2+ in a biopsy taken post-progression during/after 1st-line therapy, but HER2-negative by blood-based NGS. Disease assessments per RECISTv1.1 will occur q6 weeks for 36 weeks, then q9 weeks. The pharmacokinetics of TUC, Pac, and their metabolites will be evaluated in a subset of pts, including a cohort with gastrectomies. Enrollment is ongoing in the U.S. Clinical trial information: NCT04499924.

TPS468 Background: Trastuzumab (T), a monoclonal antibody (mAb) targeting HER2, is standard of care palliative 1st-line therapy for advanced HER2+ GEJ/GC patients (pts). M, an Fc-engineered anti-HER2 mAb, targets the same HER2 epitope but with higher affinity for both 158V (high binding) and 158F (low binding) alleles of activating Fc receptor CD16A. M coordinately enhanced both innate and adaptive immunity, including antigen-specific T-cell responses to HER2. PD-1 and LAG-3 are T-cell checkpoint molecules that suppress T-cell function. MGA012 (INCMGA00012) is a humanized, hinge-stabilized, IgG4 κ anti-PD-1 mAb blocking binding of PD-L1 or PD-L2 to PD-1. MGD013 is a humanized Fc-bearing bispecific tetravalent protein that binds to both PD-1 and LAG-3, inhibiting their respective ligand binding. We previously reported that a CTX-free regimen of M+PD-1 blockade was well tolerated in GEJ/GC pts, and induced a 30% objective response rate (ORR). This was 2- to 3-fold greater than in historical controls with checkpoint inhibitors alone. This registration-directed trial assesses efficacy, safety, and tolerability of M+checkpoint inhibition ± CTX in metastatic/locally advanced, treatment-naïve, HER2+ GEJ/GC pts. Methods: This is a 2-cohort, adaptive open-label phase 2/3 study. The first single arm, CTX-free cohort A evaluates M+MGA012 in HER2+ (immunohistochemistry [IHC] 3+) and PD-L1+ (excluding microsatellite instability high) pts. After 40 pts are evaluated for response/safety, 60 more pts will be enrolled if the threshold for continuation is met. In randomized cohort B, HER2+ (IHC 3+ or 2+/fluorescent in situ hybridization+) pts are enrolled irrespective of PD-L1 status. Part 1 randomizes pts to 1 of 4 arms (50 pts each): control arm (T+CTX) or 1 experimental arm (M+CTX; M+CTX+MGA012; M+CTX+MGD013). CTX is investigator’s choice XELOX or mFOLFOX-6. Part 2 consists of control (T+CTX) vs 1 experimental arm (M+CTX) + either MGA012 or MGD013, depending on results from part 1; with 250 pts each. The primary efficacy endpoint for cohort A (both parts) is ORR per RECIST 1.1; for cohort B part 2 it is overall survival.

4009 Background: Interim analysis of a global, phase 2 KEYNOTE-059 study (NCT02335411) reported manageable safety and promising antitumor activity for pembro alone or pembro + chemo in pts with G/GEJ cancer. Here we report long-term efficacy and safety data of all cohorts. Methods: Pts with recurrent or metastatic G/GEJ adenocarcinoma were enrolled in 3 cohorts. Cohort 1 pts (PD-L1–positive or –negative) received pembro alone after ≥2 prior lines of therapy. Cohort 2 pts (PD-L1–positive or –negative) received pembro + cisplatin (80 mg/m2 day 1) + 5-fluorouracil (800 mg/m2 days 1-5 Q3W) or capecitabine (in Japan only, 1000 mg/m2 twice daily) as first-line. Cohort 3 pts (PD-L1–positive, combined positive score ≥1% using the PD-L1 IHC 22C3 pharmDx assay) received pembro alone as first-line. All pts received pembro 200 mg Q3W for up to 2 years. End points included safety, ORR, DOR, and OS. Results: At data cutoff (Aug 8, 2018), median (range) follow-up was 6 (1-38), 14 (2-40), and 21 (2-36) months for cohorts 1 (n = 259), 2 (n = 25), and 3 (n = 31), respectively. In cohort 1, confirmed ORR (95% CI) was 11.6% (8-16) overall, 15.5% (10-22) in PD-L1–positive, and 6.4% (3-13) in PD-L1–negative tumors. In cohort 2, confirmed ORR was 60.0% (39-79) overall, 73.3% (45-92) in PD-L1–positive, and 37.5% (9-76) in PD-L1–negative tumors. In cohort 3, confirmed ORR was 25.8% (12-45). Median (range) DOR in months was 16.1 (2-35+), 4.6 (3-37+), and not reached (2.1-32.5+) in cohorts 1, 2, and 3, respectively. OS at 1 year/2 years was 24.6%/12.5%, 52%/32%, and 63.6%/40.1% in cohorts 1, 2, and 3, respectively. In cohorts 1, 2, and 3, grade 3-5 treatment-related adverse event (TRAE) incidence was 46 (18%), 20 (80%), and 8 (26%) respectively. TRAEs led to discontinuation in 6 (2%) and 3 (12%) pts in cohorts 1 and 2, respectively, and to death in 2 (1%) pts in cohort 1. No TRAEs led to discontinuation or death in cohort 3. Conclusions: These updated results demonstrate manageable safety, durable clinically meaningful activity of pembro in heavily pretreated pts, and promising efficacy of first-line pembro (alone or + chemo) in pts with advanced G/GEJ cancer. Clinical trial information: NCT02335411.

259 Background: Belinostat is a novel histone deactylase inhibitor which demonstrates preclinical activity in HCC. We report the results of a phase I/II study on belinostat in patients (pts) with unresectable HCC. Methods: Major eligibility criteria included histologically confirmed HCC not amenable to curative treatment; PS ≤ 2; adequate organ function; prior systemic therapy was allowed. In the phase I portion, belinostat was given i.v. on D1-5 every 3 weeks with dose levels of 600, 900, 1200 and 1400 mg/m2/day. In the phase II portion, belinostat was tested at the MTD. Primary endpoint was PFS and secondary endpoints were RR according to RECIST and OS. CT assessment was done every 8 weeks. Results: Phase I portion: a total of 18 pts were accrued; no DLTs were observed at 1400mg/m2/day for 5 days, and this dose was selected for phase II development. Phase II portion: 42 pts were accrued; Median age = 57.5 years; 41 had Child’s A function, and 24 pt had ECOG 0. Sixteen (38%) had previous systemic therapy, and 21 (50%) had previous transarterial therapy. Median follow-up was 20.0 months. The PR and SD rate was 2.4% (1/42) and 45.2% (19/42). Median PFS was 2.64 months (95%C.I. 1.55-3.17) and OS was 6.60 months (95%C.I. 4.53-11.60). Grade 3 or higher toxicities (>5% rate) were abdominal pain (9.5%), (9.5%) hyperbilirubinemia (9.5%), raised ALT (9.5%); anemia (7.1%) and vomiting (7.1%). Conclusions: Belinostat demonstrates disease stabilization in a predominantly pretreated population of pts with unresectable HCC with an acceptable safety profile. Further randomized studies are warranted.Supported in part by N01-CM-62205.