‘Idiopathic’ eosinophilia with an Occult T-cell clone: Prevalence and clinical course

In a study of 99 consecutive patients with ‘idiopathic’ eosinophilia, clonal T-cells were demonstrated in blood, bone marrow, or other tissue samples of 14 patients including 6 who had an overt T-cell malignancy. The remaining eight patients (∼8%) with an ‘Occult’ T-cell clone had predominantly cutaneous disease and FIP1L1-PDGFRA was absent in all six evaluable patients. Two patients were effectively treated with low-dose oral cyclophosphamide or methotrexate whereas Gleevec® treatment was ineffective in another two patients. Two patients (25%) transformed into cutaneous T-cell lymphoma after 3–8 years of eosinophilic prodrome.