On September 16, 2021 MacroGenics, Inc. (NASDAQ: MGNX), a biopharmaceutical company focused on developing and commercializing innovative monoclonal antibody-based therapeutics for the treatment of cancer, reported results from Cohort A Part 1 of the Phase 2/3 MAHOGANY clinical trial of margetuximab (Press release, MacroGenics, SEP 16, 2021, View Source [SID1234587802]). MARGENZA (margetuximab-cmkb) is approved in HER2+ metastatic breast cancer and is being investigated as a potential first-line treatment for patients with HER2+ gastric cancer (GC) or gastroesophageal junction (GEJ) cancer in combination with a checkpoint inhibitor, with or without chemotherapy. The dataset is available in a poster titled "Margetuximab With Retifanlimab in HER2+, PD-L1+ First-Line Unresectable/Metastatic Gastroesophageal Adenocarcinoma (GEA): MAHOGANY Cohort A" (Poster #1379P) at the 2021 European Society for Medical Oncology (ESMO) (Free ESMO Whitepaper) Virtual Conference taking place September 16-21, 2021.
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The efficacy data and safety cutoff dates were July 19, 2021 and August 3, 2021, respectively. In Cohort A Parts 1 and 2, the efficacy and safety of combining margetuximab and retifanlimab (investigational anti-PD-1 monoclonal antibody licensed to Incyte by MacroGenics) is planned to be evaluated in approximately 100 patients whose tumors are HER2+ at the 3+ level by immunohistochemical (IHC) staining, PD-L1+ (combined positive score ≥1%) and non-microsatellite instability-high (non-MSI-H). A pre-specified interim analysis assessing efficacy and safety was conducted on the first 40 non-MSI-H patients enrolled in Part 1. These data support advancement to Part 2 with plans to enroll approximately 60 additional response-evaluable non-MSI-H patients.
A total of 43 HER2 3+ and PD-L1+ patients were enrolled in Cohort A Part 1 and received margetuximab 15 mg/kg plus retifanlimab 375 mg/kg administered intravenously every three weeks. Twenty-five patients (58%) had gastric cancer and 18 patients (42%) had gastroesophageal junction cancer; 36 patients (84%) had metastatic disease at study entry.
MAHOGANY Cohort A Interim Analysis
Anti-tumor activity was observed in patients treated with margetuximab plus retifanlimab in MAHOGANY Cohort A after the first scan. Tumor shrinkage was observed in 32 of 41 patients (78%) with at least one post-baseline target lesion measurement. Twenty-one of 40 response-evaluable patients achieved an objective response (53%, 95% confidence interval (CI): 36%-69%), including four confirmed complete responses and 17 confirmed partial responses. The number of confirmed responders by independent assessment exceeded the prespecified futility boundary for the trial, and enrollment is proceeding to Cohort A Part 2.
Disease control was achieved in 29 of 40 patients (73%, CI: 56%-85%) and the median duration of response was 10.3 months (range: 2.1 – 14.5 months, CI: 4.6 months – not evaluable (NE)). Median progression-free survival (PFS) was 6.4 months by independent assessment (CI: 6.0 months – NE); median overall survival (OS) was not yet reached. At both 12 and 18 months, OS was 85% (CI: 63%-95%).
Antitumor activity was comparable to historical data from the experimental arm of the Trastuzumab for Gastric Cancer (ToGA) study (trastuzumab + chemotherapy; n=294; objective response rate (ORR) of 47%; median duration of response (DOR) of 6.9 months)1 and initial data from the control arm (placebo + trastuzumab + chemotherapy) of the KEYNOTE‐811 study (ORR of 52%; median DOR of 9.5 months).2
The safety analysis of all 43 patients treated with margetuximab plus retifanlimab suggests the combination was well tolerated in the study population. The most common TRAEs were fatigue (21% Grade 1-2, 0% Grade ≥3), infusion-related reaction (19% Grade 1-2, 0% Grade ≥3), rash (19% Grade 1-2, 0% Grade ≥3), diarrhea (16% Grade 1-2, 2% Grade 3), and pruritus (16% Grade 1-2, 0% Grade ≥3). A total of nine Grade 3 TRAEs were reported in eight patients (19%); no Grade 4 TRAEs were observed. Eight serious TRAEs were reported in seven patients. Infusion-related reactions considered as adverse events (AEs) of special interest occurred in six patients.
Treatment-emergent AEs of Grade 3 occurred in 18 of 43 patients (42%) of patients. Three of 43 patients (7%) discontinued therapy due to immune-related AEs: renal dysfunction (Grade 3), hepatitis (Grade 3), and diabetic ketoacidosis (Grade 1); no AEs led to death.
Safety data from MAHOGANY compare favorably to the experimental arm of ToGA in which overall Grade 3-4 AEs were 68% and the treatment-related mortality was 3%.1 Initial results from KEYNOTE-811 data presented at the 2021 ASCO (Free ASCO Whitepaper) Annual Meeting indicated that AEs of Grade 3-5 occurred in 57.1% of patients in the experimental arm (pembrolizumab + trastuzumab + chemotherapy) and in 57.4% of patients in the control arm, AEs leading to death occurred in 3.2% vs 4.6%, and AEs leading to discontinuation of any study drug occurred in 24.4% vs 25.9% of patients, respectively. Despite limitations of cross-study comparisons, regimens containing chemotherapy may have clinically relevant safety differences compared to the chemotherapy-free regimen in MAHOGANY Cohort A.
"We are excited to share our results from the interim analysis of Part 1 of the MAHOGANY Cohort A study at ESMO (Free ESMO Whitepaper)," said Scott Koenig, M.D., Ph.D., President and CEO of MacroGenics. "This study is designed to support potential registration of margetuximab in combination with other agents for patients with gastric or gastroesophageal junction cancer as part of our strategy to advance margetuximab in HER2+ cancer. The findings suggest the combination of margetuximab and retifanlimab may potentially provide a chemotherapy-free option as a first-line treatment for patients whose tumors are positive for both HER2 and PD-L1. We are pleased these data support the protocol’s prespecified advancement into Part 2 of MAHOGANY Cohort A. We plan to discuss these results and future development of the combination in an upcoming scheduled meeting with the FDA."
ESMO Presentation
MacroGenics’ Cohort A Part 1 MAHOGANY Study poster presentation is available for on-demand viewing on the ESMO (Free ESMO Whitepaper) website and on the "Events & Presentations" page on MacroGenics’ website at View Source
The MAHOGANY Study Design
MAHOGANY (NCT04082364) is a Phase 2/3 clinical trial in two cohorts designed to evaluate margetuximab in combination with a checkpoint inhibitor, with or without chemotherapy, as a potential first-line treatment for patients with advanced or metastatic HER2+ GEJ/GC.
Cohort A is designed as a single arm study to test margetuximab plus retifanlimab (previously known as MGA012 and INCMGA00012), an investigational anti-PD-1 monoclonal antibody, in patients with HER2+ and PD-L1+ tumors. The primary outcome measure for efficacy is ORR per Response Evaluation Criteria in Solid Tumors (RECIST 1.1).
Cohort B is designed as a randomized trial to test margetuximab plus a checkpoint inhibitor in combination with chemotherapy compared to standard of care therapy of trastuzumab with chemotherapy in patients with HER2+ tumors irrespective of PD-L1 expression. Patients randomized to one of two experimental arms containing a checkpoint inhibitor will receive either retifanlimab or tebotelimab (previously known as MGD013), an investigational DART molecule targeting PD-1 and LAG-3. The primary outcome measure for efficacy is OS.
The Phase 2/3 clinical trial is being conducted at clinical sites globally, in collaboration with Zai Lab, the company’s regional partner in Greater China. For additional information about the MAHOGANY study, please visit View Source
About Gastric and Gastroesophageal Junction Cancer
Cancer of the stomach (gastric cancer, GC), or the gastroesophageal junction (GEJ) where the esophagus joins the stomach, is collectively known as gastroesophageal adenocarcinoma and is the fifth most common tumor type worldwide. Both GC and GEJ cancer are often diagnosed at an advanced stage and therefore have very poor prognosis, with a 5-year survival of 5-20%. Chemotherapy is the standard of care for first-line therapy and may be combined with trastuzumab for the approximately 20% of patients whose tumors are HER2+.
About Margetuximab
MARGENZA (margetuximab-cmkb) is approved in HER2+ metastatic breast cancer and is being investigated as a potential first-line treatment for patients with HER2+ GC or GEJ cancer in combination with a checkpoint inhibitor, with or without chemotherapy. Margetuximab is an Fc-engineered monoclonal antibody that targets the HER2 oncoprotein. HER2 is expressed by tumor cells in breast, gastroesophageal and other solid tumors. Through MacroGenics’ Fc Optimization technology, margetuximab has been engineered to enhance the engagement of the immune system.
Margetuximab is also being evaluated in combination with tebotelimab (PD-1 × LAG-3 bispecific DART molecule) in various HER2+ tumors (NCT03219268). MacroGenics is partnered with Zai Lab for the development and commercialization of margetuximab in Greater China. For more information, please visit www.clinicaltrials.gov.
About Retifanlimab
Retifanlimab is an investigational, humanized, proprietary anti-PD-1 monoclonal antibody being developed for use as monotherapy as well as in combination with other potential cancer therapeutics. Retifanlimab was licensed to Incyte Corporation in 2017 under an exclusive global collaboration and license agreement. MacroGenics retains the right to develop its pipeline molecules with retifanlimab. Incyte is pursuing development of retifanlimab monotherapy in four potentially registration-directed trials for patients with MSI-high endometrial cancer, Merkel cell carcinoma, anal cancer and non-small cell lung cancer. Incyte and MacroGenics are each conducting multiple studies of retifanlimab in combination with other agents.
About Tebotelimab
Tebotelimab is an investigational, first-in-class bispecific DART molecule designed to provide co-blockade of PD-1 and LAG-3 for the potential treatment of a range of solid tumors and hematological malignancies.