Comparison of Clinical Outcomes Between Pediatric Aplastic Anemia and Refractory Cytopenia of Childhood
Authors: Hama Asahito , Manabe Atsushi , Hasegawa Daisuke , Nozawa Kazue , Narita Atsushi , Muramatsu Hideki , Takahashi Yoshiyuki , Watanabe Kenichiro , Ohara Akira , Ito Masafumi , Kojima Seiji 
Published: October 2019

Abstract
In the diagnosis of childhood bone marrow failures (BMFs), differentiating aplastic anemia (AA) from hypoplastic myelodysplastic syndrome (MDS) is challenging. The 2008 World Health Organization (WHO) classification has proposed a provisional entity, "refractory cytopenia of childhood (RCC)". The spectrum of patients with RCC is wide, ranging from patients with severe hypocellular bone marrow (BM) and mild dysplasia to those with normocellular BM and distinct dysplasia meeting the criteria for refractory cytopenia with multilineage dysplasia (RCMD) defined for adults with MDS. Currently, it is recommended that children who meet the criteria for RCMD should be classified as RCC in the WHO classification until the number of lineages involved has been fully evaluated with regard to their relative importance as prognostic factors. Until now, few studies have addressed the question whether the current WHO classification reflects clinical outcomes of childhood BMFs.
To determine the clinical differences among AA, RCC, and RCMD, we compared clinical outcomes for patients with AA, RCC, and RCMD in Japan. From February 2009 to December 2013, 252 patients were registered to the central morphology review system of the Japanese Society of Hematology and Oncology and were diagnosed with BMFs. Peripheral blood (PB) and BM smears were reviewed by two pediatric hematologists, and BM trephine biopsies were reviewed by a hematopathologist. RCC is defined as persistent cytopenia with <2% and <5% blasts in PB and BM, respectively. BM aspirate smears show dysplastic changes in >2 cell lineages or >10% within one cell lineage. On the other hand, the criteria of RCMD is defined as persistent cytopenia with <1% and <5% blasts in PB and BM, respectively. BM smears show >10% dysplastic changes in >2 cell lineages. Patients with inherited BMFs were excluded by family history and physical examination. Further, Fanconi anemia was excluded by chromosome fragility test　and Dyskeratosis congenita was screened by measuring the telomere length of the peripheral lymphocytes by flowcytometry.
Out of 252 patients, 63 were classified as AA, 131 as RCC, and 58 as RCMD. Median ages in AA, RCC, and RCMD groups were 10, 8, and 7 years, respectively (p=0.07). The median of leukocyte, neutrophil, reticulocyte, and platelet count, and mean corpuscular volume were significantly lower in AA than in RCC and RCMD groups (p<0.01). Chromosomal abnormalities were detected in 1 patient with AA (trisomy 8), 3 patients with RCC (trisomy 8, n=2; other, n=1), and 9 patients with RCMD (trisomy 8, n=5; monosomy 7, n=1; other, n=3) at the time of diagnosis (p<0.01). Out of 252 patients, 82 (AA, n=3; RCC, n=46; RCMD, n=33) were observed without any treatments (watch and wait, WW). 5-year overall survival (OS)/failure free survival (FFS) rates in WW group were 67%/67% in AA, 98%/54% in RCC, and 100%/69% in RCMD patients (p<0.01/p=0.97). Immunosuppressive therapy (IST) with rabbit antithymocyte globulin and cyclosporine was performed in 110 (AA, n=39; RCC, n=57; RCMD, n=14) patients. Six months after the IST, the response rates to the IST were not significantly different among AA (40%), RCC (63%), and RCMD (64%) (p=0.08). The development of additional chromosomal aberrations was found in 2 patients with RCC, and 1 with RCMD. The 5-year OS/FFS rates in IST group were 89%/36% in AA, 94%/38% in RCC, and 93%/23% in RCMD patients (p=0.64/p=0.86). Stem cell transplantation (SCT) as a first line therapy was performed in 19 patients with AA, 10 with RCC, and 5 with RCMD. The rejection was found in 2 patients with RCC and 3 with RCMD. Although 5-year OS rates in patients who underwent SCT were not different among 3 groups (p=0.26), FFS rate (30%) in patients with RCMD was significantly lower than in those with AA (100%) and RCC (78%) (p<0.01).
In conclusion, we could not find any clinical relevance of separating RCC from AA because response rates to IST and the development of clonal evolution did not significantly differ between AA and RCC. The entity of RCMD should be adopted to childhood MDS classification because children with RCMD exhibited a distinct characteristic of morphology and a frequent chromosomal aberration at the time of diagnosis. The optimal treatment strategy including preconditioning regimen of SCT should be established for children with acquired BMFs based on the BM cellularity and morphological classification.

Disclosures
Kojima: SANOFI: Honoraria, Research Funding.