KLRB1 and acute lymphoblastic leukemia: CD56, a marker of natural killer (NK) cell differentiation, defines a rare subgroup of about 3% of adult ALL cases which often display other early T-cell antigens, CD7 CD2 CD5, and sometimes cCD3.19 True NK ALL is very rare (TdT+, CD56+, other T markers negative, unrearranged TCR genes).21 This diagnosis rely on the demonstration of early NK-specific CD94 or CD161 antigens.