Summary Seven patients with hypereosinophilia in association with a lymphoblastic malignancy are described. The eosinophilia preceded or was present at diagnosis in all patients. Eosinophil counts fell during complete remission but rose significantly before or during relapses in five patients. Hypogranular and sometimes Pelgereosinophils were seen in five cases. Surface and enzyme markers defined the malignancy in six cases as common-ALL (three), T-ALL (two) and T-lymphoblastic lymphoma (one). Although a diagnosis of eosinophilic leukaemia or acute myeloid leukaemia with cosinophil differentiation was considered in three patients, cytochemical and ultrastructural studies failed to show any evidence of myeloid differentiation in the blast cells. The bone marrow karyotype was normal in the four patients studied.
All seven patients had one or more relapses and six died 6–62 months from diagnosis. Severe complications of the hypereosinophilic syndrome developed in one patient.
As T-lymphocytes have been shown to be involved in the induction of eosinophilia in rodents, it is suggested that the hypereosinophilia in these patients was induced by eosinopoietic stimuli produced by lymphoblasts.