RT-PCR in Diagnosis and Disease Monitoring of Acute Promyelocytic Leukemia (APL)
	Acute promyelocytic leukemia (APL) is one of the most common subtypes of acute myeloid leukemia (AML), accountmg for 10–15% of de novo cases and typically presenting in early middle age (1  ). The disease is characterized by a potentially devastating coagulopathy that can lead to rapid demise, particularly owing to cerebral hemorrhage (1  ), a balanced chromosomal translocation, t(15;17), that is present in virtually all cases of morphological APL (2  –5  ) and a unique treatment response to retinoids (6  –9  ). Development of APL reflecis two critical processes: leukemic transformation coupled with a block in myeloid differentiation causing the bone-marrow to become replaced by abnormal promyelocytes (10  ). Retmoids, for example all-trans retinoic acid (ATRA) or 9-cis retinoic acid (9-cis RA), release this block at the promyelocyte stage, such that complete remission is achieved by terminal differentiation of the leukemic clone rather than by a cytotoxic effect (7  –9  , 11  –12  ). Clinical trials have demonstrated that retinoids can achieve remission rates in APL that match those of conventional chemotherapy; indeed remission has even been induced in patients that were previously resistant to chemotherapeutic agents (7  –9  ).
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