[Beneficial effect of 1,25-dihydroxyvitamin D3 in the treatment of myelofibrosis].

Two cases of myelofibrosis are reported, one corresponding to a chronic idiopathic myelofibrosis and another to an acute myelofibrosis or megakaryoblastic leukemia (AMGL). According to current knowledge, the origin of fibrosis in these disorders is a megakaryoblastic/megakaryocytic proliferation in the bone marrow. These megakaryocytic clonal populations result in an ineffective megakaryocytopoiesis and in an inability to store beta-thromboglobulin (BTG), platelet factor 4 (PlF4) and platelet derived growth factor (PDGF) in the alpha granules, whereby their release is increased. Both PDGF, a powerful stimulator of fibroblastic activity, and PlF4, a collagenase inhibitor, cooperate in the development of myelofibrosis. Owing to its action inducing cellular differentiation towards the monocytic-macrophagic line, which secretes collagenases and inhibits megakaryocyte proliferation, treatment with 1,25-dihydroxyvitamin D3 was attempted in both cases, 2.5 micrograms daily for 6 months. Satisfactory results were achieved.