Prognostic factors and efficacy of postoperative chemotherapy in patients with gastric cancer with positive peritoneal cytology after gastrectomy.

Background: Peritoneal lavage cytology-positive (CY1) gastric cancer (stage IV) has a poor prognosis, though some cases fare better. Therefore, identifying prognostic factors and an optimal treatment strategy is crucial.

Aim: To investigate prognostic factors in patients with gastric cancer who underwent gastrectomy with CY1, and to evaluate the optimal postoperative chemotherapy regimen.

Methods: This multicenter retrospective cohort study analyzed prognostic factors and postoperative chemotherapy in patients with CY1 gastric cancer who underwent gastrectomy, excluding those with macroscopic peritoneal dissemination. Data from 13 institutions (2015-2019) were reviewed.

Results: Overall, 82 patients met the inclusion criteria. The median overall survival was 22.8 months, and diffuse-type histology and the absence of postoperative chemotherapy were identified as independent poor prognostic factors. The 5-year survival rate was 82.4% for those receiving fluoropyrimidine plus docetaxel/oxaliplatin vs 21.8% for those with S-1 monotherapy or a cisplatin-based regimen. Median overall survival was not reached in the fluoropyrimidine + docetaxel/oxaliplatin group but was 22.9 months in the S-1/cisplatin group. Chemotherapy regimen was an independent prognostic factor (hazard ratio = 5.47, P = 0.004). The fluoropyrimidine plus docetaxel/oxaliplatin group had an average relative dose intensity of 82.1%, with significantly more patients achieving a relative dose intensity ≥ 80% than in the S-1 monotherapy or cisplatin-based group (P = 0.001).

Conclusion: Diffuse-type histology and the absence of postoperative chemotherapy influence the prognosis of patients with CY1 gastric cancer. Combination therapy with oxaliplatin or docetaxel may enhance the treatment intensity and improve survival outcomes after gastrectomy.