CTI BioPharma Corp, a biopharmaceutical company, announced that it received written communication from the US Food and Drug Administration (FDA) on February 4, 2016, that the FDA has placed a partial clinical hold on the clinical studies being conducted under the company's Investigational New Drug (IND) application for pacritinib. This clinical hold impacts part of the clinical work currently being conducted under the IND and will also affect planned clinical trials.

Under the partial clinical hold, clinical investigators may not enroll new patients or start pacritinib as initial or crossover treatment, and patients not deriving benefit after 30 weeks of pacritinib treatment should stop using pacritinib. In addition, the FDA has recommended that the company make certain modifications of protocols, including modifying all protocols for randomized trials to disallow crossover to pacritinib, provide certain notifications, revise relevant statements in the related investigator's brochure and informed consent documents, and take certain other actions. The company intends to implement the FDA's recommendations. All clinical investigators worldwide have been delivered a notice of the partial clinical hold.

The company intends to work together with the FDA and expects to submit modifications and revisions that address the recommendations noted above. In its written notification, the FDA cited the reasons for the partial clinical hold were that there was excess mortality and other adverse events in pacritinib-treated patients compared to the control arm in the PERSIST-1 trial. The excess mortality was most evident during the non-randomized crossover period following the initial 24 weeks of randomized treatment, during which patients in the control arm could switch to pacritinib treatment. In prior correspondence, the FDA acknowledged the difficulty addressing non-significant results, and that crossover designs can confound the interpretation of safety as well as the evaluation of survival.

After submission of the required information, the FDA has indicated that it would notify the company whether it can continue the clinical studies under the IND.

Additionally, CTI BioPharma announced that as of February 3, 2016, it has completed patient enrollment in the PERSIST-2 phase 3 clinical trial of pacritinib for the treatment of patients with myelofibrosis. PERSIST-2 is evaluating pacritinib for patients with myelofibrosis whose platelet counts are less than or equal to 100,000 per microliter (=100,000/µL). Under the FDA partial clinical hold referenced above, patients currently receiving pacritinib may continue to do so unless they are not deriving benefit after 30 weeks of pacritinib treatment, and crossover of patients from the control arm to the pacritinib arm will not be allowed.