Rare adult acute lymphocytic leukemia with CD56 expression in the ECOG experience shows unexpected phenotypic and genotypic heterogeneity

Expression of CD56, a marker of natural killer (NK) cells, in acute lymphoc ytic leukemia (ALL) is rare and, to date, has been described only in non-B lineage ALL. Among 194 patients with CD56 analysis on the ongoing Eastern C ooperative Oncology Group (ECOG) ALL trial, E2993, 6 cases of CD56(+) ALL w ere found (3.1%) with a median of 95% of blast cells expressing CD56, compa red with a median of 1% of blast cells in CD56(-) ALL (P = 0.0001). FAB-L2 characteristics dominated, without granulation. Blast cells from four CD56( +) patients expressed T-cell antigens at variable levels of maturation. A c lonal rearrangement of the T-cell receptor beta (TCR beta) gene was detecte d only in one patient. TCR beta variable gene usage studies in this and one other CD56(+) ALL patient demonstrated a significantly perturbed usage pat tern in both patients when compared with control lymphocytes, The two remai ning cases typed as early pre-B ALL (CD19(+), CD10(+)), with one case co-ex pressing CD7, Cytogenetically, 4 patients were normal, 1 complex abnormal, and 1 Philadelphia chromosome positive. Epstein-Barr virus (EBV) sequences were detected in one T- and both B-lymphoid cases. Our data suggest that CD 56 is expressed at a precursor stage common to the T- and the B-cell lineag e. Am. J, Hematol, 66:189-196, 2001, (C) 2001 Wiley-Liss, Inc.