Schematic diagram of NPM and ALK proteins in normal cells and in t(2;5)-positive lymphoma cells and the resulting immunostaining patterns. This scheme assumes that NPM and NPM-ALK are present in both monomeric and dimeric forms in approximately equal numbers, and does not show larger oligomers that might form.5 It may thus represent an oversimplification of what occurs in vivo. (a) In a normal cell, NPM is confined to the nucleus. In a cell carrying the (2;5) translocation, NPM-ALK is found in the cytoplasm and other NPM-ALK that has heterodimerized with wild-type NPM has acquired nuclear localization. (b) Immunostaining for N- and C-terminal epitopes of NPM and for ALK show distinctive patterns, reflecting the localization of the proteins in the scheme shown above.