How Targeted Therapies and Persistent Monitoring Led to Long-Term Remission

In December 2019, a 67-year-old man visited his local hospital complaining of persistent abdominal pain. An esophagogastroduodenoscopy (EGD) revealed ulcerative changes in the stomach’s antrum, and biopsy results confirmed a poorly differentiated adenocarcinoma. Further immunohistochemistry tests identified negative HER2neu and a PD-L1 combined positive score (CPS) of 1%, classifying the tumor as microsatellite stable (MSS). A computed tomography (CT) scan then uncovered local invasion into the pancreas and carcinomatosis, leading to a Stage IV (cT4aN2M1) diagnosis.

First-line treatment began in February 2020 with XELOX chemotherapy, showing a minor reduction in tumor size by May 2020. Pressurized intraperitoneal aerosol chemotherapy (PIPAC) followed in June, revealing a low peritoneal cancer index (PCI) of 1. Additional chemotherapy and a second PIPAC session in August maintained the PCI at 1. However, the patient soon developed pyloric stenosis, necessitating a gastroenterostomy.

By November 2020, imaging indicated disease progression, including new liver metastases. The therapy was changed to paclitaxel plus ramucirumab, but a subsequent CT scan revealed further spread. In January 2021, the patient switched to pembrolizumab, leveraging his PD-L1 status. Remarkable improvements surfaced by April 2021, with a significant decrease in the primary tumor and liver metastases.

Despite a two-month treatment break due to COVID-19 infection, scans in September 2021 revealed no active liver or lymph node involvement. Pembrolizumab continued until December 2021, when the tumor showed new signs of growth. Because there were no distant metastases, a laparoscopic distal gastrectomy with D2 lymphadenectomy was performed. Postoperative histology revealed a well-differentiated adenocarcinoma confined to the muscle layer and no lymph node involvement.

For over 22 months since surgery, the patient has remained treatment-free without any sign of recurrence, highlighting how a tailored therapeutic strategy combined with timely intervention can overcome even the most advanced gastric cancer cases.