Long-term interferon-alpha 2A does not induce sustained hematologic remission in younger patients with essential thrombocythemia

The ability of Interferon alpha (alpha-IFN) to alter the natural history of essential thrombocythemia (ET) and induce sustained hematologic remission would provide further impetus to consider this agent in younger patients wi th this disease and may influence the decision to commence treatment in asy mptomatic patients. This study has failed to demonstrate any sustained hema tologic remissions after cessation of long-term (2 years) alpha-IFN adminis tration in a group of 34 female patients with a median age of 41 years (ran ge 14-68) who were considered at intermediate to high risk of thrombotic co mplications. In the twenty-one patients completing two years of therapy, 13 (62%) had complete hematological responses (CHR; platelet count <400 x 10( 9)/L), 7 (33%) partial hematological responses (PHR; platelet count 400-600 x 10(9)/L) and no thrombotic or hemorrhagic complications occurred. In all patients who discontinued alpha-IFN at 2 years, platelet counts rose above the normal range within 1 - 4 months and the majority required reinstituti on of some form of therapy. The inability of long-term alpha-IFN to induce sustained, unmaintained hematologic remission argues strongly against any s ignificant effect on the neoplastic clone at the doses used in this study. This study does, however, confirm the efficacy of long-term alpha-IFN in yo unger female patients with ET, a group not previously well represented in c linical trials of the agent.