GSTM1 and anemia (phenotype): Age (age ≤ 45 years, >45 years), gender, T stage, N stage, clinical stage, Epstein-Barr Virus (EBV) DNA (<4000 copies/ml, ≥4000 copies/ml), Hb continuous decrease (continuous decrease, no-continuous decrease), ΔHb (<2.2 g/dl, ≥2.2 g/dl), pre-treatment Hb level (anemia, no-anemia), mid-treatment Hb level (anemia, no-anemia), and post-treatment Hb level were regarded as factors in the multivariable analysis.