Two cases of extramedullary acute promyelocytic leukemia. Cytogenetics, molecular biology, and phenotypic and clinical studies

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Abstract
Background. The extramedullary collection of leukemic cells is an infrequent complication of myeloid leukemias, and extremely uncommon in acute promyelocytic leukemia (APL). Methods. The case reports of two patients with APL who relapsed with extramedullary disease and a review of the literature are presented. Results. Two patients with cytogenetically and molecularly confirmed APL developed extramedullary relapse in skin and lymph nodes after prior treatment with all-trans retinoic acid. A review of the literature revealed only nine cases of APL complicated by extramedullary disease. However, only one of these previously reported patients was shown to have the cytogenetic abnormality characteristic of APL. Conclusions. To the authors' knowledge, These two patients represent the first cases of cytogenetically confirmed APL treated with all-trans retinoic acid who developed extramedullary relapse. These events, which were reported infrequently in patients treated only with cytotoxic therapy, may be more common in patients receiving all-trans retinoic acid. In view of the differentiating activity of all-trans retinoic acid, which may increase the migratory capacity of these malignant cells, it is hypothesized that this agent may predispose some patients to unusual forms of relapse.