Clinical Relevance of p53 Immunohistochemical Stain in the Differential Diagnosis Between Pediatric Aplastic Anemia and Refractory Cytopenia of Childhood

Dear Editor, Refractory cytopenia of childhood (RCC) is the most common subtype of hypoplastic myelodysplastic syndrome (hMDS) in childhood, characterized by persistent cytopenia, dysplastic changes in erythroid precursors or megakaryocytes, and the presence of erythroid islands, defined as more than 10 erythroid precursors in a bone marrow (BM) biopsy section [1, 2]. Since 75% of the patients with RCC show hypocellularity, it is challenging to differentiate RCC from other BM failure disorders such as pediatric aplastic anemia (AA). In contrast with its wild type, which has short half-life, the mutant p53 protein has a relatively long half-life and is thus detectable through p53 immunohistochemical (IHC) stain [3]. The clinical usefulness of p53 IHC on BM cells, which can be evidence of mutation in the TP53 gene, has been reported for discriminating hMDS from AA [4-6]. We evaluated the clinical relevance of p53 IHC stain in the differential diagnosis between RCC and pediatric AA. Retrospectively, this study included 53 patients (28 men, 25 women; age 2-16 yr, median 8.5 yr) diagnosed as having pediatric AA in the Asan Medical Center, Seoul, Korea, from January 2002 to July 2012. The diagnosis of pediatric AA was reconfirmed following criteria described in the literature [7]. Clinical and laboratory data, including paroxysmal nocturnal hemoglobinuria (PNH) test results and karyotype at diagnosis, were obtained by reviewing the medical record. BM aspiration and biopsy slides at diagnosis were reviewed by two hematopathologists, and the diagnosis of possible RCC was assessed according to three morphologic findings: (1) the presence of erythroid islands consisting of at least 10 immature erythroid precursors in the BM biopsy or clot section; (2) the presence of at least three