On September 22, 2017, the U.S. Food and Drug Administration (FDA) granted accelerated approval to pembrolizumab (Keytruda) for patients with recurrent locally advanced or metastatic, gastric or gastroesophageal junction adenocarcinoma whose tumors express programmed cell death ligand 1 (PD-L1) as determined by an FDA-approved test. Patients must have had disease progression on or after two or more prior systemic therapies, including fluoropyrimidine- and platinum-containing chemotherapy and, if appropriate, HER2/neu-targeted therapy.
The FDA also approved the PD-L1 IHC 22C3 pharmDx (Dako), to select patients with gastric cancer for treatment with pembrolizumab. If PD-L1 expression is not detected in an archival gastric cancer specimen, the FDA recommends assessing the feasibility of a fresh tumor biopsy.
Approval is based on the results of KEYNOTE-059, (ClinicalTrials.gov Identifier NCT02335411) an open-label, multicenter, noncomparative, multicohort trial that enrolled 259 patients with gastric or gastroesophageal junction adenocarcinoma. Among the 259 patients, 55% (n = 143) had tumors expressing PD-L1 and either microsatellite stable (MSS), undetermined microsatellite instability (MSI), or mismatch repair (MMR) status.
PD-L1 expression was evaluated by the PD-L1 IHC 22C3 pharmDx Kit and PD-L1 positivity was based on a combined positive score ≥ 1. Combined positive score is determined by the number of PD-L1–staining cells (tumor cells, lymphocytes, macrophages) divided by the total number of tumor cells evaluated, multiplied by 100.
For the 143 patients with tumors expressing PD-L1 and who were either MSS or had unknown MSI or deficient-MMR status, the objective response rate was 13.3% (95% confidence interval: 8.2%–20.0%); 1.4% had complete responses and 11.9% had partial responses. Among the 19 responding patients, the response duration ranged from 2.8+ to 19.4+ months, with 11 patients (58%) having response durations of 6 months or longer and 5 patients (26%) having response durations of 12 months or longer.
Among the 259 patients enrolled in KEYNOTE-059, 7 (3%) had tumors that were determined to be MSI-high. Responses were observed in 4 of these 7 patients (overall response rate 57%), with 1 complete response. The response duration ranged from 5.3+ to 14.1+ months.
Adverse reactions occurring in patients with gastric cancer were similar to those presently described in product labeling. The most common adverse reactions are fatigue, musculoskeletal pain, decreased appetite, pruritus, diarrhea, nausea, rash, pyrexia, cough, dyspnea, and constipation. Pembrolizumab is associated with immune-mediated side effects, including pneumonitis, colitis, hepatitis, endocrinopathies, and nephritis.
The recommended pembrolizumab dose for gastric cancer is 200 mg administered as an intravenous infusion over 30 minutes every 3 weeks until disease progression, unacceptable toxicity, or up to 24 months in patients without disease progression.
Information on FDA-approved tests for PD-L1 expression in NSCLC or in gastric cancer is available at http://www.fda.gov/CompanionDiagnostics. ■