SUSTAINED COMPLETE HEMATOLOGICAL REMISSION IN ESSENTIAL THROMBOCYTHEMIA AFTER DISCONTINUATION OF LONG-TERM ALPHA-IFN TREATMENT

In essential thrombocythemia patients alpha-IFN rapidly reduces platel et count, and it is also able to maintain a low count during long-term treatment. In order to verify if long-term IFN treatment can produce sustained remission in selected patients, we decided to suspend IFN tr eatment in two subsets of 21 patients on long-term alpha-IFN treatment : (a) all six patients who had shown a platelet count below 450 x 10(9 )/1 for at least 2 months with 3 MU once a week; (b) three patients wh o had shown the same platelet count for at least 2 months with 3 MU th ree times a week. After withdrawal of alpha-IFN treatment, a rapid inc rease in the platelet count was observed in all three patients requiri ng 3 MU three times a week. Three of the six patients treated with 3 M U once a week are still free of symptoms and have been in complete hem atological remission (platelet count below 450 x 10(9)/l) for 9+, 13+, and 14+ months, respectively. As far as the three remaining cases are concerned, one was not assessable because of loss to follow-up, while the other two relapsed after 1 and 2 months. We believe that the thre e cases of sustained remission might be the result of a long-term tumo r load reduction produced by the alpha-IFN treatment. Finally, the fac tor best able to predict sustained, unmaintained remission seems to be the clinical response to a low dose of alpha-IFN during the maintenan ce phase, rather than disease features prior to treatment.