 Patients will be assessed in the clinic every two months after starting treatment. Hydroxyurea will be started at 10 mgkgday, and increased by 5 mgkgday at eight week intervals if needed to reach a maximum tolerated dose MTD. The most common side effect of the drug is a drop in infection fighting cells, or white blood cells, so the medication will be started at a low dose and the dose will be increased only if it is safe to do so. 