CHICAGO (TheStreet) -- The CTI Biopharma (CTIC) drug pacritinib is mostly effective for a small percentage of myelofibrosis patients with dangerously low platelet counts, according to new data from a phase III study presented Saturday afternoon at the American Society of Clinical Oncology (ASCO) annual meeting.
Myelofibrosis patients with higher platelet counts appear to benefit more from treatment with Incyte's (INCY) Jakafi, based on a cross-trial comparison. To date, the two drugs have not been compared directly against each other in a clinical trial.
CTI Biopharma announced top-line results from the phase III study known as PERSIST-1 last March. The pacritinib spleen response rate was 19.1%, compared with 4.7% for best alternative therapy, achieving the primary endpoint of the study with statistical significance.
Myelofibrosis is a disorder in which abnormal bone marrow stem cells produce scar tissue that replaces healthy marrow. Patients with myelofibrosis suffer from anemia and enlarged spleens. Patients with 35% or greater reduction in the size of their spleen after 24 weeks of treatment were considered responders in the pacritinib study.
Incyte secured approval for Jakafi, in part, on studies of myelofibrosis patients which demonstrated a spleen response rate of 32% after 24 weeks. But Jakafi causes platelet counts to fall, so some myelofibrosis patients can't take the drug or must reduce the dose.
Of the 327 myelofibrosis patients enrolled in CTI Biopharma's phase III study, 15% had baseline platelet counts of 50,000 units or less -- too low to be treated with Jakafi.