A randomized study that compared IV iron to oral iron in 502 anemic patients with cancer revealed that the Hb response was notably better in the IV iron group, particularly for those who received ≥ 80% of the planned dose and had a TSAT < 20%, whereas the response was reduced and the time to response was longer in patients with a TSAT of 20–50% [40]. The gene discussed is GSTM1; the disease is cancer.