CD56 expression predicts occurrence of CNS disease in acute lymphoblastic leukemia

We examined the pre-treatment bone marrow samples from 200 consecutive adult patients with acute lymphoblastic leukemia (ALL) treated on various protocols at the University of Texas, M.D. Anderson Cancer Center between 1986 and 1998. Standard MFC techniques were used to determine CD56 expression on the leukemia blasts cells. The expression of CD56 was correlated with clinical characteristics at diagnosis, response to therapy, survival and disease-free survival. Blast expression of CD56 (> or = 20% of leukemic blasts) was seen in 16 (8%) of patients, with a median expression of 67% (range 20-99%). CD56 expression was associated with a higher incidence of central nervous system (CNS) disease at diagnosis (19% versus 4%; P=0.016). Incidence of CNS disease at any time was higher in patients with CD56+ disease (31% versus 14%; P=0.057). Among the 109 patients uniformly treated with the hyperCVAD regimen, CD56 expression was associated with a statistically significant higher incidence of CNS disease (33% versus 9%; P=0.026). CD56 expression in ALL is uncommon but may predict a higher risk for CNS disease. If these results are confirmed, CD56 expression could be used in combination with other high-risk features (e.g. lactate dehydrogenase (LDH), S-phase fraction, mature B-cell phenotype) to design a risk-oriented approach to CNS prophylaxis.