Relapsed APL patient with variant NPM–RARα fusion responded to arsenic trioxide-based therapy and achieved long-term survival

Current first- and second-line treatment options in acute promyelocytic leukemia

Outcome of acute promyelocytic leukemia (APL) has remarkably improved during the last 30 years, especially after the identification of PML-RARA oncogene as a key in the pathogenesis of APL and all-trans retinoic acid as therapeutic agent. Arsenic trioxide has been recently demonstrated to be the most effective single antileukemic agent and it has also showed synergistic action when combined with all-trans retinoic acid, decreasing relapse rate especially in low/intermediate-risk settings. Therapeutic advances led to complete remission rates of more than 90%, modifying disease history. In relapse setting, arsenic trioxide-based regimens showed efficacy for the achievement of second molecular complete remission. The most challenging issue in APL management remains the significant early deaths rate, nowadays the principal reason for treatment failure.

Molecular Characteristics and Clinical Significance of 12 Fusion Genes in Acute Promyelocytic Leukemia: A Systematic Review

Acute promyelocytic leukemia (APL) is characterized by the generation of the promyelocytic leukemia-retinoic acid (RA) receptor α (PML-RARα) fusion gene. PML-RARα is the central leukemia-initiating event in APL and is directly targeted by all-trans-RA (ATRA) as well as arsenic. In classic APL harboring PML-RARα transcripts, more than 90% of patients can achieve complete remission when treated with ATRA combined with arsenic trioxide chemotherapy. In the last 20 years, more than 10 variant fusion genes have been found and identified in APL patients. These variant APL cases present different clinical phenotypes and treatment outcomes. All variant APL cases show a similar breakpoint within the RARα gene, whereas its partner genes are variable. These fusion proteins have the ability to repress rather than activate retinoic targets. These chimeric proteins also possess different molecular characteristics, thereby resulting in variable sensitivities to ATRA and clinical outcomes. In this review, we comprehensively analyze various rearrangements in variant APL cases that have been reported in the literature as well as the molecular characteristics and functions of the fusion proteins derived from different RARα partner genes and their clinical implications.

Acute Promyelocytic Leukemia: A Review and Discussion of Variant Translocations

The majority of patients with acute promyelocytic leukemia (APL) manifest the t(15;17)(q24.1;q21.2) translocation; however, a minor but significant proportion of patients with APL harbor complex, cryptic, or variant translocations, which typically involve RARA. With the exception of ZBTB16/RARA, these variants have similar morphologic and immunophenotypic features as classic APL. Study of the variant forms of APL not only gives insight into the pathogenesis of APL but also allows us to understand the mechanism of retinoid therapy. It is important to identify these cryptic and variant translocations because certain variants, including ZBTB16/RARA and STAT5B/RARA, are resistant to treatment with all-trans retinoic acid, arsenic trioxide, and anthracyclines.

Impact of arsenic trioxide in the treatment of acute promyelocytic leukemia

Arsenic trioxide (ATO) is presently the most active single agent in the treatment of acute promyelocytic leukemia (APL). This review provides insights into the mode of action and the pharmacological properties of ATO, and summarizes the most relevant results of more than 20 treatment studies in relapsed or newly diagnosed APL published between 1997 and 2011. ATO acts by targeting multiple pathways in APL leading to apoptosis and myeloid differentiation. It induces complete remission without myelosuppression and causes only few adverse effects. In relapsed APL, ATO-based salvage therapy has been able to induce long-lasting remissions and possible cure in 50-81% of patients. In newly diagnosed APL, two main strategies are currently pursued. ATO is either included into induction therapy with the aim to minimize or eliminate chemotherapy, or it is incorporated as an additive into established first-line concepts with all-trans-retinoic acid and chemotherapy to reinforce their anti-leukemic efficacy. Recent results suggest a high efficacy of ATO in both concepts. In conclusion, experimental research and clinical studies have made contributions toward a better understanding of the molecular mechanisms induced by ATO in APL cells and have established this historic substance as an important candidate for the further improvement of APL therapy.