Introduction
Immunotherapy has emerged as an important treatment in many types of malignancy. In 2017, the FDA granted accelerated approval to pembrolizumab in the third line setting for patients with PD-L1 positive recurrent locally advanced or metastatic gastric or gastroesophageal junction adenocarcinoma based on the KEYNOTE-059 trial (1). In the KEYNOTE-062 trial, first line pembrolizumab for treatment of advanced gastric or EG junction adenocarcinoma was shown to be non-inferior to chemotherapy (2). Patients with a CPS score >10 in the trial had an improvement in overall survival compared to chemotherapy. Pembrolizumab now has approval for first-line treatment of these patients based on this trial. Many oncologists find immunotherapy to be particularly useful in patients who may not be ideal candidates to receive chemotherapy given its excellent side effect profile and ability to achieve a durable response. This has made checkpoint inhibitor therapy standard of care in the first line setting in advanced or metastatic gastric adenocarcinoma with a CPS score >10.
There are many reports of patients who discontinue immunotherapy but continue to have a durable response, especially in those patients who experienced an immune-related adverse event (irAE). This has specifically been documented in melanoma, where the use of immunotherapy has become commonplace (3).
We present a case of a patient with metastatic gastric adenocarcinoma who received only three doses of pembrolizumab and sustained a prolonged response with near resolution of her disease nine months after the discontinuation of treatment.