Dysplastic Changes and Proliferation Index in Acquired Aplastic Anemia Are Not Associated with Progression to MDS/AML - a Study of Bone Marrow in Children and Adults
Authors: Marchesi Raquel Ferrari , Velloso Elvira Deolinda Rodrigues Pereira , Garanito Marlene Pereira , Kumeda Cristina Aiko , Siqueira Sheila Aparecida Coelho , Azevedo Neto Raymundo Soares , Zerbini Maria Claudia Nogueira 
Published: October 2019

Abstract
Acquired Aplastic Anemia (AAA) is a rare disease which progresses to MDS / AML in up to 15% of cases. When this happens, hematopathologists are asked whether the diagnosis of hypocellular Myelodisplastic Syndrome (h-MDS) would not have been confused morphologically with aplastic anemia.
This study aims to identify morphological/immunophenotypical (M/I) findings that could predict this adverse prognosis in adults and children (<19y) diagnosed as AAA and verify if those criteria match with the ones described in literature in adult h-MDS (Bennett JM, Orazi A. Diagnostic criteria to distinguish hypocellular acute myeloid leukemia from hypocellular myelodysplastic syndromes and aplastic anemia: recommendations for a standardized approach. Haematologica, 2009;94:264-9)¹ and, more recently, in pediatric MDS (Baumann I, Niemeyer CM, Bennett JM, et al. Childhood Myelodisplastic Syndrome. In: Swerdlow SH, Campo E, Harris NL, et al (Ed.). WHO Classification of Tumours of Haematopoietic and Lymphoid Tissues. Fourth Edition. Lyon: IARC Press, 2008:104-7)², contributing to the discussion of this "grey zone".
We retrospectively analyzed 123 patients/bone marrow (BM) biopsies at the moment of AAA diagnosis at Clinical Hospital of São Paulo Medical School from 1993 to 2012. Diagnosis of AAA was carried out according to classical criteria (Marsh JCW. et al. Guidelines for the diagnosis and management of aplastic anaemia. British Journal of Haematology, 2009;147:43-70). Evolution to MDS or AML was considered in the presence of at least one of the findings: significant dysgranulopoiesis or dysmegakaryocytopoiesis, more than 15% ring sideroblasts, blasts in peripheral blood or more than 5% blasts in bone marrow smear and/or biopsy, or in the presence of monosomy or deletion of the long arm of chromosome 7 by cytogenetic analysis (FISH or karyotype) of the BM. All biopsies were submitted to morphological (see Table 1) and immunophenotypic (MPO, Glycophorin A, Factor VIII, CD34, CD117 and Ki-67) evaluation by two hematopathologists without previous knowledge nor about the evolution of the patients neither cytogenetic analysis results. Nominal qualitative variables were analyzed by using Fisher's exact test to check significant disproportion between the groups. The ordinal qualitative variables were analyzed for differences between groups by Mann-Whitney test. The significance level was 5% (a = 0.05). The correlation between the overall cellularity values ​​of the samples and their proliferative index was evaluated by nonparametric Spearman r test.
Seventy three (59%) were male, median age 25,3 years (7 months to 76years), 42 belongs to the pediatric group and 81 to the adults group. Median follow-up was 5,1y (range, 1 month to 22,1 years). Twelve patients (9,7%) (6 in each group) progressed to MDS/AML.
Evaluation of M/I parameters are presented in Table 1. Criteria described by Bennett and Orazi¹ suggestive of h-SMD evaluated in our study were marrow dysgranulopoiesis, marrow dysplasia of megakaryocytes and CD34-positive blast cells in the presence of at least one of the previous two. Criteria described by Baumann et al.² suggestive of childhood MDS evaluated in our study were marrow dysgranulopoiesis, clusters of at least 20 erythroid precursors (1), increased number of proerythroblasts (2), increased number of mitoses of the erythroid elements (3) (criteria counted if 1+2, 1+3 or 2+3 were observed) and marrow dysplasia of megakaryocytes.
There was no statistically difference in M/I findings as well as the presence of Bennett and Orazi¹ criteria for MDS and Baumann et al.² criteria for childhood MDS among total population, adults and children who developed and did not develop MDS/AML. There was a statistically significant correlation between the overall cellularity values of the samples and their proliferative index.
Adult and pediatric patients with AAA, including those that progress to MDS/AML, have similar M/I characteristics. Some changes described by Baumann for pediatric MDS are also found in pediatric and adults cases with AAA. In addition, the proliferative index may be increased in cases of AAA and this finding has no correlation with progression to MDS/AML. M/I changes in bone marrow biopsies in AAA have failed to identify a group at higher risk for progression to MDS/AML in our series.
Table 1 Table 1.

Disclosures
No relevant conflicts of interest to declare.