Shares of Spectrum Pharmaceuticals Inc. fell 17 percent Monday after the Irvine, Calif.-based biotech said it had received a complete response letter from the FDA for its supplemental biologics license application (sBLA) for Zevalin (ibritumomab tiuxetan) as a first-line consolidation therapy in patients with non-Hodgkin's lymphoma (NHL).
The company's stock (NASDAQ:SPPI) closed at $5.40 Monday, a loss of $1.10.
Paul Arndt, senior manager of investor relations at Spectrum, said regulators requested data files from the Phase III FIT study the firm used for its subset analyses during labeling negotiations with the FDA but did not ask for additional clinical studies or new analyses of submitted data.
"So it is not like we have to do a whole new trial," he told BioWorld Today. "This is something very minor, in our opinion."
Arndt said his firm plans to respond to the FDA no later than Wednesday. "We are still very comfortable and very confident that Zevalin will be approved in the first-line consolidation setting," he said.
Nonetheless, Arndt said, Spectrum was caught off guard last Thursday night by the complete response letter.
"This was a complete surprise," he said. "This was clearly not the response we were expecting. We were expecting either a positive or, if anything, maybe a couple of days extension," given that the FDA recently has been missing its Prescription Drug User Fee Act action dates.
But, he said, "We were not expecting a complete response." Arndt said it was unclear when a potential approval may come on the sBLA.
"The FDA will respond whenever they respond," he said. "But we feel very confident."
Zevalin, an anti-CD20 monoclonal antibody linked to the radioisotope Yttrium-90, currently is approved in the U.S. as a treatment for patients with relapsed or refractory, low-grade or follicular B-cell NHL, including patients who have rituximab-refractory follicular NHL.
When it was first approved in 2002, the drug was administered in the hospital setting only, primarily in large academic centers. However, more oncologist group practices have invested in PET scan technology and have nuclear medicine specialists or radiation oncologists on site, which make those practices more ideally suited to administer Zevalin.
As a consolidation therapy, Arndt explained, Zevalin "aims to rapidly improve the quality of the response achieved with initial remission induction treatment."
Spectrum's sBLA was based on its multinational, randomized Phase III First-line Indolent Trial, or FIT, which evaluated the benefit and safety of a single infusion of Zevalin in 414 patients with CD20-positive follicular NHL who had achieved a partial response or a complete response after receiving one of the standard first-line chemotherapy regimens.
The FIT trial demonstrated that Zevalin significantly improved the median progression-free survival time from 13 months to 37 months.
The results showed that there was a total complete response rate of 87 percent and prolongation of median progression-free survival by about two years, with a toxicity profile comparable to that seen with the drug's use in the approved indications.
In March, Spectrum bought out the 50-50 joint venture established to commercialize Zevalin, known as RIT Oncology LLC, from Seattle-based Cell Therapeutics Inc. for $16.5 million. (See BioWorld Today, Feb. 24, 2009.)
CTI acquired Zevalin from Cambridge, Mass.-based Biogen Idec Inc. in 2007 for $10 million up front. Biogen also stood to gain $20 million in milestone payments and royalties on sales. (See BioWorld Today, Aug. 17, 2007.)
But when Spectrum acquired all of RIT Oncology, the firm assumed all of the joint venture's obligations to Biogen and other licensors, Arndt said.
Upon achievement of certain Zevalin-related FDA milestones, Spectrum will be required to pay Biogen $5.5 million, he added.