A Phase II Study of Oral Interferon-Alpha (IFN-a) for Patients with Essential Thrombocythemia or Polycythemia Vera.

Recombinant human IFN-α has been the mainstay of therapy for patients with Philadelphia chromosome-negative myeloproliferative disorders for many years. However, the response rates of IFN-α therapy have been frequently challenged by high dropout rates due to side effects and inconvenient subcutaneous dosing schedules. Accordingly, we design a phase II study to evaluate the efficacy and safety of natural human IFN-α administered by the oral mucosal route in patients (pts) with essential thrombocythemia (ET) or polycythemia vera (PV). Pts were eligible if they had failed (inability to normalize platelet count in ET, or to reduce the frequency of phlebotomy or splenomegaly by 50% in PV, after 6 months of therapy with hydroxyurea (HU) and anagrelide (AG)), were intolerant to HU and AG, or refused to receive standard cytoreductive therapy. HU or AG therapy had to be stopped at least 3 weeks prior to start of oral IFN-α. Prior exposure to IFN-α was not allowed. Oral IFN-α was administered at 150 IU three times daily as a lozenge. A total of 14 pts (8 PV, 6 ET) have been treated. Median age was 57 (range, 32 to 79), time from diagnosis to oral IFN-α therapy 2 months (range, 0 to 32), Hb 14.2 gm/dL (range, 11.2 to 15.4), WBC 9.75 ×10⁹/L, (range, 5.6 to 17.3), platelets 812 ×10⁹/L (range, 360 to 1389). Five patients were previously treated with HU, four with AG, and 3 with imatinib mesylate. Six pts with PV had received phlebotomies and 2 presented with marked splenomegaly. The JAK2 V617F mutation was detected in 10 of 11 evaluated pts and 2 of 14 pts (14%) had abnormal cytogenetics. All 14 pts are evaluable for response and toxicity. No responses have been observed among any of the 14 pts treated. Ten (71%) pts discontinued oral IFN-α therapy due to lack of response (n=9) or disease progression (n=1, elevation of platelets), and 4 are currently on therapy. Duration of therapy varied: 2.5 months = 2 pts, 3 months = 6 pts, 4 months = 4 pts, 6 months = 2 pts. Therapy with oral IFN-α was very well tolerated: grade 1 headache was noted in 2 pts, and grade 1 paresthesia in 1 pt. We conclude that oral IFN-α is very well tolerated but has no activity in the treatment of pts with ET or PV at the dose and schedule employed in this study.