PDCD1 and cancer: There were seven studies involving 3395 cases and 2912 controls for PD-1 rs2227981, four studies including 1961 cases and 2390 controls for PD-1 rs2227982, four studies with 1975 cases and 2403 controls for PD-1 rs7421861, and four studies for PD-1 rs11568821 variant and cancer risk.