SUMMARY: The FDA on May 5, 2021 granted accelerated approval to KEYTRUDA® (Pembrolizumab) in combination with Trastuzumab, Fluoropyrimidine and Platinum-containing chemotherapy for the first-line treatment of patients with locally advanced unresectable or metastatic HER2 positive Gastric or GastroEsophageal Junction (GEJ) adenocarcinoma. The American Cancer Society estimates that in the US, about 26,560 new cases of Gastric cancer will be diagnosed in 2021 and about 11,180 people will die of the disease. It is one of the leading causes of cancer-related deaths in the world. Several hereditary syndromes such as Hereditary Diffuse Gastric Cancer (HDGC), Lynch syndrome (Hereditary Nonpolyposis Colorectal Cancer) and Familial Adenomatous Polyposis (FAP) have been associated with a predisposition for Gastric cancer. Additionally, one of the strongest risk factor for Gastric adenocarcinoma is infection with Helicobacter pylori (H.pylori), which is a gram-negative, spiral-shaped microaerophilic bacterium.
Majority of the patients with Gastric and GastroEsophageal (GE) Adenocarcinoma have advanced disease at the time of initial presentation and have limited therapeutic options with little or no chance for cure. The Human Epidermal growth factor Receptor (HER) or erbB family of receptors, consist of HER1, HER2, HER3 and HER4. Approximately 15-20% of advanced Gastric and GastroEsophageal (GE) junction cancers, overexpress or have amplification of the HER2 oncogene. These patients often receive first line treatment with a combination of chemotherapy plus anti-HER2 antibody, Trastuzumab, as there is Overall Survival (OS) benefit with this combination regimen.
KEYTRUDA® is a fully humanized, Immunoglobulin G4, anti-PD-1, monoclonal antibody, that binds to the PD-1 receptor expressed on activated T cells, and blocks its interaction with ligands PD-L1 and PD-L2. It thereby reverses the PD-1 pathway-mediated inhibition of the immune response and unleashes the tumor-specific effector T cells. In two Phase II studies, KEYTRUDA® in combination with Trastuzumab and chemotherapy showed promising efficacy with manageable toxicities.
The present FDA approval was based on KEYNOTE-811 trial, an ongoing global, multicenter, randomized, double blind, placebo controlled, Phase III study, which assessed whether adding KEYTRUDA® to Standard of Care chemotherapy improved efficacy, compared to Standard of Care alone, among patients with HER2+ metastatic Gastric/GEJ cancer. A total of 692 patients were enrolled and patients were randomized (1:1) to receive KEYTRUDA® 200 mg IV or placebo IV every 3 weeks, in combination with Trastuzumab and investigator’s choice of Fluorouracil plus Cisplatin (FP), or Capecitabine plus Oxaliplatin (CAPOX). Treatment is being given for up to 2 years or until intolerable toxicity or progressive disease. Patients were enrolled irrespective of PD-L1 status, and HER2-positive status was defined as ImmunoHistoChemistry (IHC) 3+ or IHC 2+ and FISH positivity. The dual Primary end points are Progression Free Survival (PFS) by Blinded, Independent Central Review (BICR) and Overall Survival (OS). Secondary end points are Overall Response Rate (ORR) and Duration of Response (DOR) assessed by BICR, and Safety.
The first interim analysis included 264 patients with a median follow up of 12 months. At the time of this interim analysis, 133 patients were randomized to KEYTRUDA® plus Standard of Care and 131 patients to Placebo plus Standard of care. Approximately 88% and 85% of the patients in the KEYTRUDA® and Placebo groups respectively, had a PD-L1 Combined Positive Score of 1 or more.
The confirmed ORR was 74.4% for KEYTRUDA® plus Standard of Care versus 51.9% for Placebo plus Standard of care (P=0.00006). The Complete Response rate was 11.3% versus 3.1% and Disease Control Rate was 96.2% versus 89.3% respectively. The median Duration of Response was 10.6 months for patients treated with KEYTRUDA® and 9.5 months for those in the placebo group. Adverse Events were similar between the two treatment groups and immune-mediated pneumonitis and colitis were more common as expected, in the KEYTRUDA® group.
It was concluded that the addition of KEYTRUDA® to Trastuzumab and chemotherapy, as first line therapy for HER2+ metastatic Gastric/GE Junction cancer, resulted in a substantial, statistically significant increase in Overall Response Rate, compared to Trastuzumab and chemotherapy alone. The authors added that these initial data are practice-changing and support KEYTRUDA® plus Trastuzumab and chemotherapy as a potential new treatment option for this patient group.
Pembrolizumab plus trastuzumab and chemotherapy for HER2+ metastatic gastric or gastroesophageal junction (G/GEJ) cancer: Initial findings of the global phase 3 KEYNOTE-811 study. Janjigian YY, Kawazoe A, Yanez PE, et al. DOI: 10.1200/JCO.2021.39.15_suppl.4013 Journal of Clinical Oncology 39, no. 15_suppl (May 20, 2021) 4013-4013.