Background: Effectiveness of protein-bound polysaccharide K (PSK) during adjuvant chemotherapy in gastric cancer patients expressing programmed death-1 ligand 1 (PD-L1) has not been investigated. Investigating this might help in triaging candidates eligible to immunochemotherapy.
Materials and methods: In total, 918 patients with stages II and III gastric cancer, undergoing curative gastrectomy, and receiving adjuvant chemotherapy were enrolled in a prospective database, and the patients were retrospectively reviewed. We classified those patients into four cohorts stratified by PD-L1 expression and PSK administration, namely PD-L1, PSK (-,+); PD-L1, PSK (-,-); PD-L1, PSK (+,+); and PD-L1, PSK (+,-). In addition, another independent cohort of 20 patients undergoing radical gastrectomy was prospectively recruited to check their immunological cells of sera before and 2 mo after PSK administration.
Results: PSK treatment was an independent prognostic factor for patient's overall survival (P = 0.020), whereas PD-L1 expression per se was not. Administration of PSK prolonged patient survival in stages IIIA and IIIB (P = 0.031) but not in stage II or stage IIIC. Patients with negative expression of PD-L1, treated with PSK had longer survival than those not treated with PSK (P = 0.033). PSK did not affect the survival of patients with positive expression of PD-L1, (P = 0.421). The percentages of natural killer and natural killer T (NKT) cells, but not Th1, Th17, Treg, or IFN-γ+/CD8+ T cells, were significantly increased in PD-L1 (-) patients treated with PSK. However, these findings were not evident in PD-L1 (+) patients.
Conclusions: PSK treatment preferentially confers a survival gain for patients with stage IIIA/IIIB gastric cancer, especially in the PD-L1 (-) subpopulation.
Keywords: Gastric cancer; Natural killer cell; PD-L1; PSK; Prognosis.
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