Treatment of myelodysplastic syndromes with low-dose oral 6-thioguanine.

Several cytotoxic agents when used in vitro in very low concentrations have been shown to induce differentiation of leukemic cells. We treated 18 patients with myelodysplastic syndromes with low-dose oral 6-thioguanine (6-TG; 20 to 60 mg daily). Four patients demonstrated significant improvement in peripheral blood counts. An additional three patients had significant reductions in the percentage of leukemic myeloblasts in the marrow without a corresponding improvement in peripheral counts. With the exception of a fall in the peripheral neutrophil count in four patients requiring dose reductions, no toxicity was observed. Low-dose oral 6-TG gives a response rate in myelodysplastic syndromes similar to that of parenteral agents such as cytosine arabinoside. Given the ease of administration and lack of toxicity, oral 6-TG may be a useful treatment modality for these syndromes either alone or in combination with other differentiation-enhancing agents.