Modified Array-based Comparative Genomic Hybridization Detects Cryptic and Variant PML-RARA Rearrangements in Acute Promyelocytic Leukemia Lacking Classic Translocations:

Pediatric Acute Promyelocytic Leukemia: Epidemiology, Molecular Features, and Importance of GST-Theta 1 in Chemotherapy Response and Outcome

Previous studies have suggested a variation in the incidence of acute promyelocytic leukemia (APL) among the geographic regions with relatively higher percentages in the Latin American population. We aimed to explore the population burden of pediatric APL, gathering information from the population-based cancer registry (PBCR) and the diagnosis of APL obtained through incident cases from a hospital-based cohort. The homozygous deletion in glutathione S-transferases (GSTs) leads to a loss of enzyme detoxification activity, possibly affecting the treatment response. Mutations in the RAS pathway genes are also considered to be a key component of the disease both in the pathogenesis and in the outcomes. We have assessed mutations in a RAS–MAP kinase pathway (FLT3, PTPN11, and K-/NRAS) and GST variant predisposition risk in the outcome. Out of the 805 children and adolescents with acute myeloid leukemia (AML) who are registered in the PBCR, 35 (4.3%) were APL cases. The age-adjusted incidence rate (AAIR) was 0.03 per 100,000 person-years. One-hundred and sixty-three patients with APL were studied out of 931 AML cases (17.5%) from a hospital-based cohort. Mutations in FLT3, KRAS, and NRAS accounted for 52.1% of the cases. Patients with APL presented a 5-year probability of the overall survival (OS) of 67.3 ± 5.8%. A GST-theta 1 (GSTT1) null genotype conferred adverse prognosis, with an estimated hazard ratio of 2.8, 95% confidence interval (CI) 1.2–6.9. We speculate that the GSTT1 polymorphism is associated with therapeutics and would allow better OS of patients with APL with a GSTT1 null genotype.

Acute promyelocytic leukemia with a cryptic insertion of RARA into PML on chromosome 15 due to uniparental isodisomy: A case report

Acute promyelocytic leukemia is a myeloid disorder that is characterized by the specific t(15;17) variant in ~98% of cases. The typical hypergranular and microgranular or hypogranular types exist, and are frequently associated with disseminated intravascular coagulopathy. Rare cases of promyelocytic leukemia-retinoic acid receptor α (PML-RARA) fusion without the reciprocal RARA-PML have been reported in cytogenetically normal samples. Conversely, fluorescence in situ hybridization (FISH) analysis has revealed a cryptic insertion of the RARA gene into the PML gene on chromosome 15. The current study reports a unique case with a normal karyotype and molecular evidence of the PML-RARA short isoform 3-fusion transcript, with FISH analysis revealing two fusion signals on the two copies of chromosome 15, but absence of the reciprocal on the two copies of chromosome 17. This finding raised the hypothesis of chromosome 15 uniparental isodysomy as consequence of normal chromosome 15 loss and duplication of the rearranged chromosome, as supported by polymorphic loci molecular analysis. The clinical, cytogenetic and molecular characterization of this case are presented and discussed in the present study.

Promyelocytic Leukemia with No Retinoic Acid Receptor Alpha Abnormality but with RUNX1T1 Insertion to Chromosome 7q: A Classification and Management Dilemma

A case of acute promyelocytic leukemia (APL) with RUNX1T1 insertion to 7q is described and compared to reported cases of APL with negative retinoic acid receptor alpha (RARA) abnormality. In this report, we describe the case of a 2-year-old boy who presented with bone pain and was found to have pancytopenia. Bone marrow examination showed morphologic and immunophenotypic findings typical of APL, but conventional cytogenetics, fluorescence in situ hybridization (FISH), and real-time polymerase chain reaction (RT-PCR) showed no evidence of RARA rearrangements. The only cytogenetic abnormality found was a small insertion in 7q, and three copies of RUNX1T1. Gene sequencing results became available after initiating therapy but were not informative. We describe the rarity of such cases and discuss how the typical morphologic and immunophenotypic findings of APL, coupled with the definite absence of RARA rearrangement (by FISH and RT-PCR), present a diagnostic and classification dilemma, raising the possibility of an unknown alternative mechanism for the leukemogenesis and maturation arrest seen in other APL variants. The diagnostic challenges and urgent management issues this unusual case raises may justify including it, along with similar cases, in a separate subtype of acute myeloid leukemia (AML) in future classifications.

Extramedullary relapse in RARA rearrangement-negative acute promyelocytic leukemia successfully treated in combination with chemotherapy, local radiotherapy, and cord blood transplantation

RARA rearrangement-negative acute promyelocytic leukemia (APL) is uncommon, and its extramedullary relapse is extremely rare. We report a 5-year-old girl with RARA rearrangement-negative APL, which recurred solely at the external auditory canal and mastoid air cells. She was successfully treated with chemotherapy, local radiotherapy, and unrelated cord blood transplantation. She has maintained complete remission for 24 months after transplantation. The clinical features and our therapeutic strategy in this patient will provide valuable information for extramedullary relapse of RARA rearrangement-negative APL.

Myeloid Neoplasms with inv(3)(q21q26.2) or t(3;3)(q21;q26.2)

Acute myeloid leukemia (AML) with inv(3)(q21q26.2)/t(3;3)(q21;q26.2) [inv3/t(3;3)] is a distinct entity under the subgroup of AMLs with recurrent genetic abnormalities in the 2008 World Health Organization classification. Myelodysplastic syndrome (MDS) with inv3/t(3;3) has a high risk of progression to AML. AML and MDS with inv3/t(3;3) have a similarly aggressive clinical course with short overall survival (OS) and are commonly refractory to therapy. In this article, clinical and pathologic features and prognosis in AML and MDS with inv3/t(3;3) are reviewed, and other myeloid neoplasms with similar dysplastic features to be differentiated from AML and MDS with inv3/t(3;3) are discussed.