The Food and Drug Administration (FDA) has given its approval to a new drug developed by Gilead Sciences, which could just become another blockbuster drug from the California-based biotechnology company known for producing the HIV drug Truvada and the hepatitis C medicine Sovaldi.

Gilead's drug Zydelig (idelalisib) has been green-lighted for use as treatment for three types of blood cancer, which affect about 200,000 individuals in the U.S. In a statement released on Wednesday, July 23, the FDA said that it has given the go signal for the use of Zydelig in combination with Rituxan (rituximab) as treatment for individuals who have relapsed chronic lymphocytic leukemia (CLL).

The drug, which works by blocking the signal from the inside of cancer cells thus hampering the growth and survival of cancerous cells, is also given the go signal as treatment for patients whose follicular B-cell non-Hodgkin lymphoma (FL) or small lymphocytic lymphoma (SLL) has returned and who had two or more prior systemic therapies.

"Zydelig's approval to treat CLL reflects the promise of the breakthrough therapy designation program and represents the FDA's commitment to working cooperatively with companies to expedite a drug's development, review and approval," said Richard Pazdur, from the Center for Drug Evaluation and Research of the FDA.

The approval was granted to Zydelig as monotherapy for patients with FL and SLL under FDA's accelerated program, which allows the approval and earlier access of patients to promising new drugs for treating serious and life-threatening illnesses while the confirmatory clinical trials are still going on. The accelerated approval as treatment for FL and SLL was based on overall response rate in clinical trials. The drug attained overall response rate of 54 percent in FL patients and 58 percent in SLL patients.

"In clinical studies among patients with relapsed CLL, FL and SLL, Zydelig produced strong responses, including a significant improvement in progression-free survival in CLL. I believe it helps fill a significant unmet need for these patients," said Bruce Cheson from Georgetown University's Lombardi Comprehensive Cancer Center, who was the lead investigator of the drug's Phase 3 trial involving patients with CLL.

The newly approved drug's label will have a boxed warning highlighting the adverse reactions associated with the use of Zydelig such as diarrhea, elevated liver enzymes, hyperglycemia, liver toxicity, high blood triglycerides and colitis. Clinical trials also showed that the drug could cause abdominal pain, cough, chills, fatigue, nausea, pneumonia, fever and rash.