Adding protein-bound polysaccharide K (PSK) to adjuvant chemotherapy with mitomycin and fluorouracil after gastrectomy for gastric cancer was demonstrated to improve survival in a previous study in Japan. However, the efficacy of PSK outside Japan and in combination with other adjuvant chemotherapeutic agents remains unclear. The aims of this study were to evaluate the efficacy of PSK. We conducted a population-based historical cohort study using the National Health Insurance Research Database of Taiwan. We performed sensitivity analysis with propensity score matching to control for possible confounders. Patients who used PSK (PSK group) were matched at a 1:4 ratio to those who had never used PSK (control group) after adjusting for covariates including sex, age, urbanization, income and comorbidities. The primary outcome was overall survival. Multivariate hazard ratios from competing risk analysis were calculated by adjusting for demographic data and all confounding factors. From 1999 to 2008, we identified 10,617 patients with gastric cancer received gastrectomy and adjuvant chemotherapy. 1295 patients used PSK (PSK group) and 5180 patients never used PSK (control group) were analyzed after propensity score matching. The median overall survival was 6.49 years (95% confidence interval [CI] 5.22-7.63) in the PSK group and 3.59 years (95% CI 3.38-3.80) in the control group. After adjusting for age, sex, urbanization, income, and comorbidities, adding PSK to adjuvant chemotherapy was the most significant prognostic factor for improved survival (hazard ratio 0.76, P < .0001). Adjuvant chemotherapy combined with PSK significantly prolonged overall survival in gastric cancer patients after gastrectomy.
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