A synthetic noncalcemic, nonphosphatemic vitamin D analogue. Paricalcitol interacts with the vitamin D receptor and has been shown to reduce parathyroid hormone (PTH) levels. This agent also increases the expression of PTEN (phosphatase and Tensin homolog deleted on chromosome Ten), a tumor-suppressor gene, in leukemic cells and cyclin-dependent kinase inhibitors, resulting in tumor cell apoptosis and tumor cell differentiation into normal phenotypes. (NCI04)