Association Between the Number of Neoadjuvant Immunochemotherapy Cycles and Pathological Response in Locally Advanced Gastric Cancer: A Retrospective Cohort Study

The optimal duration of neoadjuvant immunochemotherapy for resectable locally advanced gastric cancer remains unclear. This study aimed to investigate the association between treatment cycle number and pathological response. Patients receiving neoadjuvant immunochemotherapy followed by gastrectomy were retrospectively included and categorized into 2–4-cycle and 5–8-cycle groups. The primary outcome was tumor regression grade (TRG) 0–1. Logistic regression was used to assess the association between treatment cycle group and TRG 0–1, and quadratic logistic regression was used to explore nonlinear associations. Among 409 patients, TRG 0–1 was achieved in 110 (37.3%) in the 2–4-cycle group and 58 (50.9%) in the 5–8-cycle group (p = 0.012). After multivariable adjustment, receiving 5–8 cycles was associated with a higher likelihood of achieving TRG 0–1 (adjusted OR, 1.701; 95% CI, 1.076–2.687; p = 0.023). Exploratory analysis suggested a nonlinear relationship between treatment cycle number and pathological response, with the highest estimated probability of TRG 0–1 observed at approximately 6 cycles; however, sensitivity analyses indicated that this pattern was sensitive to the inclusion of patients receiving more extended treatment. These findings require prospective validation before an optimal treatment duration can be established.