NPM1 and neoplasm: A related useful aspect of mutant NPM1 immunostaining is that it can provide helpful information when the cellularity of BM aspirate and PB specimens used for bulk studies (i.e., RT-PCR, NGS and FC) may be variable (e.g., due to a “packed-marrow”) and may underestimate tumor cell number (Sample 64, Figure 2, bottom right panel).