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.