WASHINGTON (AP) -- The Food and Drug Administration on Wednesday approved a new cancer drug from Gilead Sciences to treat three types of blood cancer.

Regulators approved the drug for patients with forms of chronic lymphocytic leukemia, follicular lymphoma and small lymphocytic lymphoma. The cancers affect an estimated 200,000 patients in the U.S., according to Gilead.

The company's tablet, Zydelig, works by blocking signals inside some cancer cells that allow them to grow and survive.

"In less than a year, we have seen considerable progress in the availability of treatments for chronic lymphocytic leukemia," said FDA's director for cancer drugs, Dr. Richard Pazdur.

The FDA has approved three other drugs for the disease in the last year: Roche's Gazyva, Janssen Pharmaceutical's Imbruvica and GlaxoSmithKline's Arzerra.

Lymphocytic leukemia first invades bone marrow cells before spreading to the blood and other parts of the body, including the liver and lymph nodes.

The FDA approved Zydelig for leukemia based on a study showing that adding the drug to another cancer therapy, Rituxan, slowed cancer progression. Researchers halted the study early when it became clear the drug was working. FDA said patients taking the Zydelig combination had the potential to live 10.7 months without their disease progressing, compared with about 5.5 months for patients taking Rituxan alone.

The drug will carry a boxed warning, the strongest type, about potentially fatal side effects, including liver toxicity, diarrhea and colon inflammation.

More common side effects with the drug include diarrhea, fever, fatigue, nausea, cough, pneumonia, chills and rash. The drug also frequently lowers white blood cell levels and raises blood sugar.

The Foster City, Calif.-based Gilead Sciences makes an array of antiviral medications used to treat HIV including Atripla, Truvada, and Stribild. The company has also made headlines this year with its breakthrough Hepatitis C drug, Sovaldi, which posted sales of $2.3 billion for the first quarter.

Analysts have estimated Zydelig could eventually reach annual sales between $1 billion and $2 billion per year.