Treatment-free remission in FIP1L1-PDGFRA-positive myeloid/lymphoid neoplasms with eosinophilia after imatinib discontinuation.

FIP1L1-PDGFRA-positive myeloid/lymphoid neoplasms with eosinophilia (MLN-eo) are exquisitely sensitive to imatinib. Almost all patients achieve a complete molecular remission (CMR) by nested reverse transcription polymerase chain reaction, which can be maintained with low-dose imatinib (eg, 3 × 100 mg/wk). Because imatinib can be safely stopped in a substantial proportion of patients with BCR-ABL1-positive CML, we sought to analyze the clinical and molecular follow-up of 12 FIP1L1-PDGFRA-positive patients with MLN-eo in chronic phase who discontinued imatinib after achievement of a CMR. Median time of treatment and median time of CMR before imatinib discontinuation (last dose at 3 × 100 mg/wk, n = 8; or 100 mg/d, n = 4) were 80 (range, 43-175) and 66 (range, 37-174) months, respectively. A molecular relapse was observed in 4 patients after 10, 22 (n = 2), and 24 months. A second CMR was achieved in 3 patients after 3, 4, and 21 months. Eight patients (62%) are in ongoing CMR (median, 17 months; range, 3-71 months). Molecular relapse-free survival was 91% at 12 months and 65% at 24 months. No significant differences (eg, dose and duration of imatinib treatment or duration of CMR before imatinib discontinuation) were identified between patients with and without molecular relapse. Our data demonstrate that imatinib can be safely stopped in FIP1L1-PDGFRA-positive MLN-eo because of a high treatment-free remission at 12 and 24 months and because most patients achieve a rapid second CMR after restart of imatinib.