[The beneficial effect of 1,25-dihydroxycholecalciferol on the excess of blasts and the myelofibrosis in 2 cases of chronic myeloproliferative syndrome].

The active metabolite of vitamin D3 1.25 dehydroxycholecalciferol (1.25DHCC) is a potent inducer of monocytic differentiation of the myeloid blasts "in vitro". Likewise the inhibiting role of vitamin D3 on bone marrow fibrosis by, among others, a stimulating effect of macrophagic activity is known. However, these actions have seldom been clinically demonstrated. Two cases of chronic myeloproliferative syndromes in which treatment with 1.25DHCC was effective are presented. In the first case, one patient with polycythemia vera with myelofibrosis and focal blastosis in the bone marrow achieved disappearance of the excess of blasts and a reduction in the fibrosis (grade III to grade I) upon treatment. In the second case, idiopathic myelofibrosis, also with focal blastosis in the bone marrow biopsy, there was no regression of the fibrosis but the blastosis did disappear. It was concluded that 1.25DHCC may constitute an interesting treatment in this group of diseases through the following two mechanisms: limitation of the fibrosis and delay of blast transformation.