p53 immunohistochemistry discriminates between pure erythroid leukemia and reactive erythroid hyperplasia

Pure erythroid leukemia (PEL) is a rare, aggressive subtype of acute myeloid leukemia with a poor prognosis. The diagnosis of PEL is often medically urgent, quite challenging, and is typically a diagnosis of exclusion requiring meticulous distinction from non-neoplastic erythroid proliferations, particularly florid erythroid hyperplasia/regeneration. Given the frequency of TP53 mutations in the molecular signature of PEL, we hypothesize that differential p53 expression by immunohistochemistry (IHC) may be useful in distinguishing PEL versus non-neoplastic erythroid conditions. We performed p53 IHC on 5 normal bone marrow, 46 reactive erythroid proliferations, and 27 PEL cases. We assessed the positivity and intensity of nuclear staining in pronormoblasts and basophilic normoblasts using a 0–3+ scale with 0 being absent (with internal positive controls) and 3 being strong nuclear positivity. A total of 26/27 PEL cases showed strong, uniform, diffuse intense staining by the neoplastic pronormoblasts versus 0/5 and 0/46 normal and reactive controls, respectively. The control cases show various staining patterns ranging from 0 to 3+ in scattered erythroid precursor cells. Uniform, strong p53 positivity is unique to PEL and discriminates this entity from a benign erythroid mimic. Thus, p53 IHC may be a useful marker in urgent medical cases to assist in the confirmation of a malignant PEL diagnosis while awaiting the results of additional ancillary studies such as cytogenetics.