Landscape of driver mutations and their clinical effects on Down syndrome-related myeloid neoplasms.

ABSTRACT: Transient abnormal myelopoiesis (TAM) is a common complication in newborns with Down syndrome (DS). It commonly progresses to myeloid leukemia (ML-DS) after spontaneous regression. In contrast to the favorable prognosis of primary ML-DS, patients with refractory/relapsed ML-DS have poor outcomes. However, the molecular basis for refractoriness and relapse and the full spectrum of driver mutations in ML-DS remain largely unknown. We conducted a genomic profiling study of 143 TAM, 204 ML-DS, and 34 non-DS acute megakaryoblastic leukemia cases, including 39 ML-DS cases analyzed by exome sequencing. Sixteen novel mutational targets were identified in ML-DS samples. Of these, inactivations of IRX1 (16.2%) and ZBTB7A (13.2%) were commonly implicated in the upregulation of the MYC pathway and were potential targets for ML-DS treatment with bromodomain-containing protein 4 inhibitors. Partial tandem duplications of RUNX1 on chromosome 21 were also found, specifically in ML-DS samples (13.7%), presenting its essential role in DS leukemia progression. Finally, in 177 patients with ML-DS treated following the same ML-DS protocol (the Japanese Pediatric Leukemia and Lymphoma Study Group acute myeloid leukemia -D05/D11), CDKN2A, TP53, ZBTB7A, and JAK2 alterations were associated with a poor prognosis. Patients with CDKN2A deletions (n = 7) or TP53 mutations (n = 4) had substantially lower 3-year event-free survival (28.6% vs 90.5%; P < .001; 25.0% vs 89.5%; P < .001) than those without these mutations. These findings considerably change the mutational landscape of ML-DS, provide new insights into the mechanisms of progression from TAM to ML-DS, and help identify new therapeutic targets and strategies for ML-DS.

Azacitidine treatment for myeloid leukemia associated with Down syndrome: A nationwide retrospective study in Japan.

Hypomethylating agent treatment for myeloid leukemia associated with Down syndrome (ML-DS) has been scarcely reported. Herein, we collected information on azacitidine treatment for ML-DS in Japan. Forty-eight cycles of azacitidine treatment were performed for 12 patients, including 11 relapsed or refractory (R/R) patients. In 40 cycles, azacitidine was used as monotherapy. No azacitidine-related death was observed. One cycle concurrently administered with methotrexate-based intrathecal therapy was discontinued due to toxicities. Only 4 of the 19 cycles given in non-remission achieved complete or partial remission. In conclusion, although most toxicities were acceptable, azacitidine monotherapy might be insufficient for R/R ML-DS cases.

Trametinib for a child with refractory Rosai-Dorfman-Destombes disease harboring a novel somatic mutation in MAP2K1.

Rosai-Dorfman-Destombes disease (RDD) is a rare histiocytosis characterized by accumulation of S100 + , CD68 + , and CD1a- histiocytes, with emperipolesis. It occurs predominantly in black adolescents and young adults, but rarely in Japanese children. Recently, oncogenic mutations in mitogen-activated protein kinase (MAPK) pathway genes were reported in 30-50% of patients with RDD, and several studies have described treatment of adult patients with MAPK inhibitors. Here, we present the case of a Japanese boy with refractory RDD without signs of cardiofaciocutaneous (CFC) syndrome who harbored MAP2K1 p.Lys59del and responded to trametinib. The patient had lymph node, nasal cavity, kidney, upper respiratory tract, and intracranial involvement. RDD progressed after multi-agent chemotherapy, but responded to trametinib (0.025 mg/kg). Trametinib did not eliminate the mass lesions, but trametinib plus minimal prednisolone (0.1 mg/kg) resulted in a good outcome for more than 15 months, without significant adverse effects. MAP2K1 p.Lys59del has been described as a germline mutation in a patient with CFC syndrome, but not as a somatic mutation in patients with malignancies. Trametinib may be a promising drug for children with RDD that is refractory to multi-agent chemotherapy. Its long-term efficacy and safety alone and in combination with chemotherapy should be investigated.