Traditional Oriental Herbal Medicine and Natural Killer Cells for Cancer Patients: A Systematic Review and Meta-analysis.

Traditional oriental herbal medicine (HM) is used by cancer patients to improve immunity. Natural killer (NK) cells are associated with development and progression of tumor and survival of cancer patients. This literature review examined randomized controlled trials (RCTs) in four electronic databases until October 2015 to evaluate the effects of oral HM on NK cells in cancer patients. Data were pooled and computed in a meta-analysis. The methodological quality was assessed according to the Cochrane risk of bias tool. Sixteen RCTs involving 1326 cancer patients were identified. Combination of HM and conventional treatment was associated with significantly higher level of NK cells compared with conventional cancer treatments (standardized mean difference, 1.218; 95% confidence interval 0.719-1.717; p < 0.001). Eight RCTs reported statistically significant improvements in the proportions or activity of NK cells in patient groups who received both HM and conventional treatment compared with patients who received conventional treatment alone, while eight RCTs reported no statistically significant differences between the two groups. Studies (n = 16) included in this review had insufficient quality of evidence with unclear (n = 1) and high (n = 15) values of the risk of bias. Although traditional oriental HM may have the positive effects on preserving the level of NK cells in cancer patients receiving conventional treatments, current evidence is inconclusive because of lack of high-quality evidence.