A phase III trial reported that olaparib-induced anemia was observed in 59.1% of patients (grade ≥ 3 anemia; 36.4%).[5] Anemia is a dose-limiting toxicity.[1] Grade ≥ 3 anemia potentially leads to treatment interruption until the recovery of hemoglobin (Hb) level ≥ 9.0 g/dL up to 4 weeks. Here, GSTM1 is linked to anemia (phenotype).