Acute promyelocytic leukemia (AML-M3)--Part 2: Molecular defect, DNA diagnosis, and proposed models of leukemogenesis and differentiation therapy.

OBJECTIVES

To identify the chromosomal translocation common in M3 and discuss its diagnostic use to: Compare acute leukemia with chronic leukemia and other forms of cancer. Describe the molecular defect including the fusion gene and fusion protein produced from the translocation. Discuss the proposed mechanism of leukemogenesis in M3. Discuss the proposed mechanism of differentiation induction stimulated by ATRA therapy. Present the future direction of this and other forms of therapy.

DATA SOURCES

Current literature.

DATA SYNTHESIS

Acute promyelocytic leukemia (AML-M3) is a form of acute leukemia that presents with a less dramatic leukocytosis, anemia, and thrombocytopenia than other acute leukemias. However, AML-M3 has a lower first remission rate and a higher morbidity and mortality rate than most of the other acute leukemias when treated with conventional chemotherapy. AML-M3 frequently stimulates a serious concomitant coagulation disorder, disseminated intravascular coagulation, which is a major contributor to the high mortality rate. This and other devastating sequela of M3 have prompted clinicians and investigators to develop methods of improving diagnosis and therapy. In 1977 the method of diagnosis confirmation was improved by the identification of a consistent chromosomal translocation involving the long arms of chromosomes 15 and 17. Identification of the specific molecular lesion that produced the t(15;17) translocation occurred in 1990 and was shown to involve the retinoic acid receptor alpha gene (RAR alpha). Because the RAR alpha gene is mutated in all AML-M3 patients studied so far and because it is often the only mutation identified, several proposed mechanisms of leukemogenesis have evolved. From these discoveries a novel approach to cancer treatment focusing on differentiation therapy instead of traditional chemotherapy emerged. All-trans retinoic acid (ATRA) has been shown to stimulate differentiation of promyelocytes from the malignant clone and has become an important element in the treatment of patients with AML-M3.

CONCLUSION

Since the discovery of the t(15;17) translocation, the identification of the fusion gene containing the retinoic acid receptor alpha, and the success of ATRA as a form of differentiation therapy, the diagnosis and treatment of AML-M3 has dramatically improved. In addition, AML-M3 has become a model system used to study the mechanisms that produce uncontrolled growth and lack of differentiation in leukemic cells (leukemogenesis) and the mechanisms of therapeutic reversal of this block in differentiation (differentiation therapy).