The patient is an 89 year old female who presented for preoperative clearance for a knee replacement surgery in May 2020 and was found to have a pulmonary nodule on chest x-ray. She reported left sided abdominal pain after eating at that time. She underwent a CT scan of the chest which showed an irregularly shaped nonspecific density involving the left lower lobe of the lung measuring 11 mm as well as multiple bilateral pulmonary nodules measuring 2 to 4 mm. She then underwent a PET scan which showed a 6 cm hypermetabolic mass in the proximal stomach with associated hypermetabolic perigastric lymphadenopathy. The lung lesions were PET negative and thought to be non-malignant. She underwent an EGD in October 2020 which showed a fungating mass in the gastric cardiac. Pathology was consistent with a poorly differentiated invasive adenocarcinoma, intestinal type.

The patient was deemed not to be a surgical candidate due to advanced malignancy and age. She was started on chemoradiation with carboplatin and paclitaxel. She completed 45 Gray and 5 cycles of chemotherapy. A PET/CT following completion of these therapies showed multifocal PET avid metastatic disease in the liver as well as metastatic lymphadenopathy to the portacaval and left para-aortic lymph nodes. Next generation sequencing was obtained and showed a PD-L1 CPS score of 50.

In February 2021 the patient initiated pembrolizumab 200 mg IV every 3 weeks. After three cycles a surveillance CT in May 2021 showed resolution of the mass in the proximal stomach as well as resolution of the adjacent perigastric lymphadenopathy. Multiple subcentimeter low-density lesions were again visualized in the liver.

In June of 2021, after three cycles of immunotherapy, the patient developed a ruptured left knee popliteal cyst associated with significant pain. She became much more sedentary because of this and also began to experience lack of appetite and fatigue. Thyroid studies, ACTH, and morning cortisol were all within normal levels. There was therefore no evidence that this was related to treatment with immunotherapy at the time. Treatment was held to allow time for the patient to recover. She showed significant improvement and at follow-up in August 2021 was back to her baseline. CT imaging performed at that time showed a decrease in size in the hepatic lesions, with a decrease in the largest lesion from 2.6 cm to 0.8 cm. The portacaval and para-aortic lymph nodes were also noted to have decreased in size. The gastric mass was again not visualized. Given that the imaging showed continued improvement in the disease despite the patient not having received immunotherapy since May 2021, the decision was made to continue to monitor off of all therapy.

Imaging was again performed in February 2022 with only one of three liver metastases still visible (Figure 1). The previously identified portacaval lymph node had resolved. She was again continued off of therapy given the remarkable durable response she attained with only three doses of immunotherapy.