The Food and Drug Administration on Wednesday approved a cancer drug from Pharmacyclics and Janssen Biotech Inc. for a new use against a rare blood and bone marrow disease.

The agency said it approved Imbruvica for patients with chronic lymphocytic leukemia who have already tried at least one other therapy. The disease causes a dangerous buildup of certain white blood cells that gradually spread from the bone marrow to lymph nodes and other organs. The National Cancer Institute estimates 15,680 Americans were diagnosed with the cancer in 2013 and 4,580 people died from the disease.

Wednesday’s action is the second approval for Imbruvica, which the FDA approved for mantle cell lymphoma in November.

The once-a-day capsule works by blocking a protein that allows the cancer to multiply and spread. Regulators approved the drug for its new use based on a study of 48 patients who had already received four other treatments, on average. Results showed 58% of patients saw their cancer shrink after using Imbruvica. Studies of the drug are ongoing and an improvement in lifespan has not yet been established.

Imbruvica is manufactured by Sunnyvale, Calif.-based Pharmacyclics and co-marketed with Janssen Biotech Inc., a unit of New Brunswick, N.J.-based Johnson & Johnson.