Aberrant expression of CD7, CD56, and CD79a antigens in acute myeloid leukemias.

The prognostic significance of selected markers of leukemic cells is well known. CD7 and CD56 expression at diagnosis has been associated with low remission rates and biological aggressiveness in a significant proportion of acute leukemias. Among 46 patients with acute myeloid leukemia, we found CD7 expression in 15 cases (32.6%) and CD56 positivity in 10 patients (21.7%). Six of these myeloid leukemia cases (13%) showed expression of both CD7 and CD56. Four of 46 (8.7%) patients expressed CD79a. Among the 10 that were acute myeloblastic leukemia, 8 expressed CD7, 4 expressed CD56, and 4 were positive for CD79a. Thus, these markers were expressed early in hemopoietic ontogeny in the lesser-differentiated acute myeloid leukemia subtypes, including FAB M0, M1, and M2. Whereas CD7 and CD56 were each positive in 4 cases of acute myelomonocytic leukemia (FAB M4 subtype), there was no CD79a expression in the M4 cases. CD7 is expressed by mature T cells, NK cells, and an immature myeloid cell subset. NK cells and a T cell subset express CD56. By contrast, CD79a is a B cell marker that is assigned a high score of 2.0 in the differentiation of acute leukemias of ambiguous lineage in the WHO classification. The aberrant expression of CD7, CD56, and CD79a, representing the capacity of these leukemias for trilineal expression of leukocyte differentiation antigens, portends a poor prognosis.