PRF1 and hemophagocytic syndrome: The targeted gene screening panel included potential causative genes from commonly mutated genes in NK-cell origin NK/T-cell lymphoma (TP53, DDX3X, STAT3, JAK3, MGA, BCOR, ECSIT, MCL1, and KMT2D) and 18 genes associated with hemophagocytic lymphohistiocytosis (PRF1, UNC13D, STX11, STXBP2, RAB27A, LYST, AP3B1, XIAP, SH2D1A, MAGT1, CD27, ITK, NBAS, NLRC4, CDC42, CD70, CTPS1, RASGRP1).