In head and neck cancer, the prevalence of anemia defined as hemoglobin (Hb) < 12.0 g/dL has been reported as 16% prior to treatment and 32% within 3–5 weeks after the first RT dose, resulting in a mean Hb decrease of 1.8 g/dL [3, 4]. Here, GSTM1 is linked to anemia (phenotype).