Therapeutic Effects of Low-Dose Cytosine Arabinoside, α-Interferon, 1,25-Dihydroxyvitamin D3 and Retinoic Acid in Myelodysplastic Syndromes and Acute Leukemia

Fifty-six patients with myelodysplastic syndrome or with acute leukemia were treated with low-dose Ara-C, a combination (IDR) of α-interferon, 1,25-dihydroxyvitamin D3 and retinoic acid or a combination of all drugs. Complete remissions were obtained only when treatment included Ara-C, but long-lasting and clinically stable partial remissions and significant responses were achieved in 7 of 16 patients treated with IDR. Bone marrow hypoplasia was not necessary for remission in any of the treatment groups. Our data indicate that these substances exert their action via mechanisms different from those seen in conventional chemotherapy. Possible mechanisms involve tumor-cell differentiation, a slow-acting cytotoxicity or a combination of these two mechanisms.