The effect of adjuvant therapy on survival in gastric cancer patients achieving pathologic complete response after neoadjuvant immunochemotherapy.

e16120 Background: Perioperative immunotherapy has significantly increased pathologic complete response (pCR) rates in locally advanced gastric cancer (LAGC). Whether adjuvant therapy provides additional survival benefit for patients (pts) with LAGC who achieve pCR after neoadjuvant immunochemotherapy remains unclear. We evaluated the association between adjuvant therapy and survival in this population. Methods: We prospectively collected clinicopathologic data on 65 consecutive pts who were diagnosed with cT3-4bN0-3M0 LAGC and were treated at Nanfang Hospital from October 2019 to May 2025. All received neoadjuvant immunochemotherapy, underwent gastrectomy, and achieved pCR (ypT0N0). Neoadjuvant regimens consisted of immunochemotherapy, with trastuzumab for HER2-positive tumors. Neoadjuvant therapy comprised 2-6 cycles. Adjuvant therapy was defined as ≥2 cycles after surgery. Pts were grouped into the adjuvant therapy group (TG, n = 44) and the no adjuvant therapy group (nTG, n = 21) according to receipt of adjuvant therapy. Survival was compared between the groups. The final follow-up was conducted on January 14, 2026, with one pt lost to follow-up. Results: Clinical stage was III in 49 pts (75.4%) and IVA in 16 (24.6%). 23.8% (15/63) of pts were dMMR, 66.7% (42/63) had PD-L1 CPS ≥5, 20.0% (12/60) were HER2-positive, and 5.5% (3/55) were EBV-positive. Overall, 85.7% (54/63) were biomarker-positive (dMMR and/or PD-L1 CPS ≥5 and/or HER2-positive and/or EBV-positive). The median number of neoadjuvant cycles was 4 (range, 2-6). In TG, immunochemotherapy was the predominant adjuvant regimen (65.9%), with a median of 4 adjuvant cycles (range, 2-6). In nTG, adjuvant therapy was not administered due to severe surgery- or treatment-related adverse events or comorbidities (8 pts, 38.1%) or refusal (13 pts, 61.9%). No significant differences were detected between the two groups in baseline clinicopathologic or neoadjuvant treatment-related characteristics. After a median follow-up of 32.0 months (IQR, 22.0-48.5), one pt in TG (CPS = 5, HER2- and EBV-negative, pMMR) relapsed at 38 months from initiation of neoadjuvant therapy and died at 40 months with extensive peritoneal metastases and massive ascites. Two additional pts in TG died of non-cancer causes (aspiration OS, 15 months; cardiac disease OS, 26 months). No recurrences were observed in nTG, and one pt died of pneumonia-related respiratory failure (OS, 30 months). No significant differences were observed between TG and nTG in 3-year EFS (93.3% vs 92.9%; log-rank p = 0.718), 3-year OS (93.8% vs 92.9%; log-rank p = 0.747), and 3-year cancer-specific survival (100% vs 100%; log-rank p = 0.552). Conclusions: In this small-sample cohort of LAGC pts achieving pCR after neoadjuvant immunochemotherapy, the recurrence rate was low, and the survival benefit observed with adjuvant therapy appeared limited.