NPM1 and neoplasm: Overall, IHC for mutant NPM1 alone is not suitable as a stand-alone assay for assessment of residual disease, but, in combination with RT-PCR, IHC can help visualize the tumor cell burden and provide information regarding neoplastic cell distribution and cell type; along these lines, mutant NPM1 staining was noted in occasional megakaryocytes, which has been previously described, indicating multilineage involvement of mutant NPM1 (25).