Spectrum Pharmaceuticals Inc. said the U.S. Food and Drug Administration denied breakthrough therapy designation for poziotinib, a therapy for a hard-to-treat lung cancer.

Poziotinib is being investigated for use in heavily pretreated patients with non-small cell lung cancer, or NSCLC, whose disease has spread across the body and with a mutation in proteins known as EGFR or HER2. Mutations in epidermal growth factor receptor, or EGFR, and human epidermal growth factor receptor 2, or HER2, have been associated with a number of different cancers.

The U.S. regulator's breakthrough status allows for an expedited review process for drugs that show improvement compared to current therapies in treating serious or life-threatening diseases. The FDA denied poziotinib the designation despite the drug showing antitumor activity in a mid-stage study.

Spectrum President and CEO Joseph Turgeon, in a conference call Dec. 19, said the decision to deny poziotinib breakthrough status came down to a judgment call from the U.S. regulator on "what is substantial and what is not."

Turgeon said the U.S. FDA requested data from 30 patients who had failed platinum-based chemotherapy after a six-month follow-up, adding that the requested results showed an objective response rate — or the percentage of patients whose tumors shrunk following treatment — of 40% after 6.6 months.

However, because of the absence of data to compare the results to, poziotinib's effectiveness in patients with mutations had to be compared to non-mutation specific non-small cell lung cancer patients, Turgeon said.

Turgeon added that the company's development plan for poziotinib remains unchanged and that Spectrum will work with the FDA to get approval for the therapy as soon as possible.

"Our enthusiasm probably is as high as it's ever been because the timeline should not change here just because you don't get BTD," he said during the call. "Our trials are set up for registration and we're confident that, that's the data that the FDA would need in order to approve this drug." Turgeon added.

Spectrum previously said it plans to develop poziotinib in previously treated NSCLC, as a first-line treatment of NSCLC, in combination with other therapies and as a treatment for other solid tumors. The company received an exclusive license from Hanmi Pharm. Co. Ltd. to develop poziotinib globally, excluding Korea and China.