Differentiation Syndrome

The incorporation of ATRA into the treatment paradigm of acute promyelocytic leukemia has significantly improved the cure rate of this disorder. ATRA causes differentiation of the malignant phenotype into a more mature myeloid cell.6263 Treatment with ATRA is generally well tolerated, but a distinct clinical syndrome has been described in treated patients. Termed variably as differentiation syndrome or the retinoic acid syndrome (RAS), it was first formally described by Frankel et al. in

1992.64 The differentiation syndrome can also occur in the setting of therapy with arsenic trioxide.

The differentiation syndrome occurs with an incidence of 6-26% in most large series.65'66 The incidence seems to be somewhat increased (26%)66 in patients treated with ATRA monotherapy, compared to 10% when combined with cytotoxic chemotherapy.67 Concurrent versus sequential administration of ATRA does not appear to alter the incidence of this syndrome. Median time to onset of symptoms is 10-12 days, but can range from 2 to 47 days.66 Typical findings include leukocytosis, fever, weight gain, dyspnea, and alreolas infiltrates on radiological examination of the chest.

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