Vitamin D

Vitamin D is a potent inhibitor of proliferation and induces cellular differentiation and maturation in vitro. Low levels of vitamin D have been found in some cases of AML and MDS. Bone marrow biopsies of several MDS patients with low normal levels of vitamin D showed depressed bone turnover without osteoporosis or osteomalacia. These findings are suggestive of osteoclast dysfunction, with a decrease in osteoblast recruitment and function.

There have been reported cases of improvement in blood counts after treatment with vitamin D, with some benefit reported in AML patients, accompanied, however, with toxic levels of vitamin D and hyper-calemia.56 Vitamin D may also induce cell differentiation through oncogene regulation, as leukemia cell lines showed a decrease in c-myc RNA levels after exposure to the drug calcitriol (a vitamin D derivative) in vitro. Blockage of cell differentiation is not characteristic of low-risk MDS, and vitamin D response in these patients is thought to be mediated by antiapoptotic effects, as observed in neoplastic cell lines.57

Nineteen patients with low- to intermediate-risk MDS were treated with vitamin D analogs: 5 patients received 266 ^g of calcifediol three times a week, and the other 14 received calcitriol (1,25(OH)2D3), the most active analog of this hormone, with escalating doses from 0.25 to 0.75 ^g/day.58 With a mean follow-up of 26 months, there was 1 response in the calcife-diol group and 10 responses (2 major responses) on calcitriol. Hypercalcemia was not observed, but no correlation was found between baseline levels of vitamin D levels and the presence of response.

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