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WASHINGTON -- The FDA has approved the novel agent (Zydelig) for treatment of three types of lymphoma in the relapse setting.

The agency granted traditional approval for treatment of relapsed (CLL) in combination with rituximab (Rituxan). The FDA granted accelerated approval of idelalisib for relapsed and relapsed (SLL).

In announcing the approval, the FDA's Richard Pazdur, MD, noted that idelalisib is the third drug approved with breakthrough designation for treatment of CLL and the fifth drug overall to receive the designation. The agency approved obinutuzumab (Gazyva) for CLL in November 2013, followed by ibrutinib (Imbruvica) in February and a new CLL indication for ofatumumab (Arzerra) in April.

"In less than a year, we have seen considerable progress in the availability of treatments for chronic lymphocytic leukemia," Pazdur, director of the Office of Hematology and Oncology Products, said in a statement. "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."

Idelalisib inhibits the delta isoform of phosphoinositide 3-kinase (PI3K), which plays a role in activation, proliferation, and viability of B cells. Several types of B-cell leukemias and lymphomas are associated with aberrant PI3K signaling.

Idelalisib received the on the basis of a randomized trial that compared rituximab with idelalisib or placebo in 220 patients with relapsed CLL unsuitable for treatment with conventional chemotherapy. The trial ended early after an interim analysis showed an 82% reduction in the hazard for progression. The median progression-free survival had yet to be reached in the idelalisib arm (95% CI 10.7 months-NR) versus 5.5 months for the placebo group (P<0.0001).

Accelerated approval for relapsed follicular lymphoma and SLL was based on results of a 98-patient phase II trial, which showed that idelalisib monotherapy led to an overall response rate of 54% in patients with follicular lymphoma and 58% in those with SLL.

The FDA is requiring a boxed warning on idelalisib's label, cautioning about the risks of fatal and serious toxicities including hepatotoxicity, severe diarrhea, colitis, pneumonitis, and intestinal perforation. FDA also approved a risk evaluation and mitigation strategy to alert healthcare providers about the risks.

Idelalisib is marketed by Gilead Sciences.

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