RESUMEN
We report a patient with massive eosinophilia and a complex karyotype that was initially misdiagnosed as chronic eosinophilic leukemia (CEL), but later diagnosed as anaplastic large cell lymphoma (ALCL) masked by massive eosinophilia. The complex karyotype observed at initial diagnosis remained unchanged later, after the evidence of bone marrow involvement of ALCL was obtained. At diagnosis, genetic aberrations corresponding to metaphase cytogenetics were not identified by interphase fluorescence in situ hybridization, although abnormal results were noted at follow-up. Together, these observations indicate that the complex karyotype at initial work-up has been derived from a low proportion of lymphoma cells with high mitotic ability that were not identified by microscopy, rather than from massive eosinophils. These findings suggest that our patient had ALCL with secondary eosinophilia rather than CEL since initial diagnosis.