# Neoadjuvant Immunotherapy Effectiveness in Patients With Microsatellite Instability-High (MSI-H) Gastric Cancer

## TL;DR

This study shows that using immunotherapy before surgery is effective and safe for patients with a specific type of advanced stomach cancer.

## Contribution

The study demonstrates the effectiveness of checkpoint inhibitor monotherapy as a neoadjuvant treatment for MSI-H gastric cancer.

## Key findings

- 77.8% of patients showed objective response to neoadjuvant CPI treatment.
- 100% of patients who underwent surgery had complete margin-free resection.
- No disease progression was observed with a median follow-up of 33.7 months.

## Abstract

Purpose

This research work evaluates monotherapy with checkpoint inhibitors (CPI). as a neoadjuvant treatment for patients with Microsatellite Instability-High (MSI-H) locally advanced gastric cancer.

Methods

Here we present the results of the retrospective study from Napalkov Cancer Center over 4.5 years on patients with MSI-H locally advanced gastric cancer. A total of 566 patients were analyzed, 18 of whom were included in the research, focusing on clinical response rate, surgical pathology, ‘watch and wait’ strategy, and safety outcomes on an exploratory basis. Patients were assigned to four to eight neoadjuvant cycles of CPI, followed by surgery.

Results

The objective response to neoadjuvant CPI in patients with MSI-H gastric cancer was 77.8%. Complete response was achieved in five (27.8%) and partial response in nine (50%) patients, accordingly. Surgery was performed on 14 patients. Complete margin-free (R0) resection rates were 100%. Downstaging was observed in 12 out of 14 patients. Histopathologic complete response rates (pathologic complete response or Tumor Regression Grade-major response (TRG1)) were achieved in eight (57.1%) patients. No disease progression was detected with a median follow-up of 33.7 months (4.4-55.7 months). Clinically significant adverse events were not observed.

Conclusion

CPI in a neoadjuvant setting for patients with MSI-H locally advanced gastric cancer is highly effective and safe.