The purpose of this study is to evaluate the safety and effectiveness of the drug vemurafenib in patients with hairy cell leukemia that persists or has returned despite prior therapy. Vemurafenib is approved for treating advanced melanoma, but its use in leukemia patients is considered investigational.
Vemurafenib works by targeting a mutated form of a protein called BRAF. Studies have shown that BRAF is altered in virtually all cases of hairy cell leukemia, so researchers want to see if vemurafenib is active against this cancer. Vemurafenib is a tablet that is taken orally (by mouth).