PD-1 inhibitors in esophageal cancer: a systematic review of the oncological outcomes associated with PD-1 blockade and the evolving therapeutic paradigm

Patients with esophageal or gastroesophageal junction (GEJ) cancer who fail to respond to chemoradiotherapy have a poor clinical prognosis. Recent clinical trials have investigated the use of immune checkpoint inhibitors in these patients. The use of programmed cell death protein 1 (PD-1) inhibitors has emerged as exciting therapeutic options in the curative and palliative setting of other solid tumors. We assessed the efficacy and safety of PD-1 inhibitors in esophageal and GEJ cancers. This systematic review was performed in accordance with the PRISMA guidelines. A comprehensive electronic literature search from the EMBASE, Pubmed, Scopus, MEDLINE, and Google Scholar databases was conducted up to 25 July 2021. This review identified 11 eligible studies reporting outcomes of 3451 patients treated with PD-1 blockade compared with 2286 patients treated with either a placebo or the standard regimen of chemotherapy. Clinically significant improvements in median overall survival have been demonstrated in advanced and metastatic esophageal and GEJ cancer while maintaining acceptable safety profiles. Promising survival data have also recently emerged from PD-1 blockade in the adjuvant setting. PD-1 blockade in esophageal and GEJ cancer has delivered impressive survival benefit while remaining well tolerated. Its use in the adjuvant setting will further advance treatment options, and more advancements in this area of therapy are highly anticipated. However, further characterization of the PD-1/programmed death ligand-1 pathway and elucidation of biomarkers to predict response are required to optimize patient selection.