# A case report of a patient with advanced gastric adenocarcinoma who demonstrated excellent long-term sustained efficacy even after discontinuation of treatment following chemotherapy combined with claudin18.2 and PD-1 therapy

## TL;DR

A patient with advanced gastric cancer showed long-term tumor shrinkage after treatment with chemotherapy, Claudin18.2-targeted therapy, and a PD-1 inhibitor, even after stopping treatment.

## Contribution

This case report demonstrates sustained tumor regression in gastric cancer after discontinuing combined therapy, suggesting a promising treatment strategy.

## Key findings

- The patient achieved partial response after seven cycles of combined chemotherapy, Claudin18.2-targeted therapy, and PD-1 inhibition.
- Despite treatment discontinuation due to aortic dissection, tumor shrinkage continued for 19 months, reaching near complete response.
- The combination therapy may offer long-term efficacy for advanced gastric cancer.

## Abstract

Gastric cancer is the fifth most common cancer and the third most common cause of cancer death globally. Patients with advanced gastric cancer have poor outcomes and short survival times. This case report presents a remarkable clinical response in a patient with advanced Epstein-Barr virus (EBV)-associated gastric adenocarcinoma treated with a combination of chemotherapy, Claudin18.2-targeted therapy (TST001), and PD-1 inhibition (nivolumab). The patient, initially diagnosed with stage IA disease (pT1bN0M0) after Billroth II gastric resection was performed due to early carcinoma, later developed metastases to the liver, cervicothoracic lymph nodes and abdominal lymph nodes. The patient received seven cycles of CAPOX (capecitabine + oxaliplatin), nivolumab, and TST001, achieving partial response (PR) after treatment. Treatment was discontinued due to aortic dissection requiring surgery. Surprisingly, despite no further antitumor therapy, follow-up imaging over 19 months revealed continued tumor shrinkage, culminating in a near complete response (CR). Therefore, the combination of chemotherapy, Claudin18.2-targeted therapy, and PD-1 inhibitor may be a good treatment strategy for gastric cancer.