Cell Therapeutics Formally Appeals FDA’s Nonapprovable Ruling for Pixantrone

Firm to conduct extra study but says statistical analyses applied to pivotal trial were too harsh.

Cell Therapeutics has submitted a formal appeal to FDA’s Center for Drug Evaluation and Research in response to the agency’s decision earlier this year not to approve the NDA for pixantrone as a treatment for relapsed/refractory aggressive non-Hodgkin lymphoma (NHL) in adult patients.

Cell Therapeutics had requested accelerated approval of the NDA for this patient group for which, the firm points out, there are currently no drugs approved. However, in April FDA’s Office of Oncology Drug Products issued a complete response letter to the NDA stating that another clinical study would be needed as the previous trial, PIX301, did not demonstrate pixantrone’s efficacy.

Cell Therapeutics is now preparing to start the extra FDA-requested trial, PIX306, which it says could alternatively serve as a post-approval confirmatory trial. A statistical consultant acting on the firm’s behalf claims that FDA applied statistical analyses that were more stringent than required for the original PIX301 study.

“We believe FDA diverged from accepted statistical principles and practices when FDA applied a more stringent statistical significant level in concluding that the PIX301 primary analysis required an adjustment for type 1 error as if an interim analysis had been conducted,” states Richard Kay, Ph.D., statistical consultant at RK Statistics and honorary visiting professor at Cardiff University’s School of Pharmacy.

“This was not the case where only a single final analysis was undertaken. We believe the results of the PIX301 clinical trial should be analyzed with the appropriate threshold that is standard for trials of this type in which only one efficacy analysis was conducted.”

Pixantrone has, meanwhile, been accepted for review by the European Medicines Agency. Just last month the agency also approved Cell Therapeutics’ Pediatric Investigation Plan for pixantrone, which will evaluate the drug as a treatment for lymphoid malignancies and solid tumors in children between the ages of 6 months and 18 years.