March 20 (HealthDay News) -- The Cephalon drug Treanda (bendamustine hydrochloride) has been approved by the U.S. Food and Drug Administration to treat chronic lymphocytic leukemia, a rare cancer that affects the blood and bone marrow.

CLL is expected to strike some 15,000 people in the United States this year, according to American Cancer Society estimates provided by the drugmaker.

In a trial of 301 patients that compared Treanda to an already approved chemotherapy drug, Treanda recipients had better response rates and longer progression-free survival, Cephalon said in a statement.

Treanda, expected to hit the U.S. market in April, works by damaging the DNA in cancer cells, causing these cells to die. Cephalon said the treatment was granted orphan drug status by the FDA, which offers companies exclusive marketing rights in return for drugs developed for rare diseases.