Correlation between expression of CD56/NCAM and severe leukostasis in hyperleukocytic acute myelomonocytic leukaemia

The possible contribution of surface molecules to the development of leukostasis syndrome in hyperleukocytic acute myeloid leukaemia (AML) was assessed by routine immunophenotyping and grading of the probability of clinical leukostasis.

Fifty-three patients (23 women, 30 men, median age 59 yr) with hyperleukocytic AML [white blood count (WBC) above 50 x 10(9)/L] were graded for the probability of clinical leukostasis according to the severity of neurologic, pulmonary and other symptoms possibly caused by leukostasis using a recently published scoring system. Age, WBC, absolute blast count, haemoglobin, cytogenetic risk group, infection, relative CD56 expression and absolute count of CD56 positive blasts were analyzed in multivariate stepwise backward logistic regression analysis.

In patients with acute monocytic leukaemia (AML M4/M5) the absolute count of leukaemic blasts expressing CD56/NCAM was highly associated with the development of symptoms graded as highly probable leukostasis and all three patients succumbing to early death were CD56 positive. Only the absolute count of CD56 positive blasts was a significant predictor of risk of severe leukostasis (P = 0.020). This was not found in AML without monocytic involvement (AML M1, M2, M3v).

The expression of CD56/NCAM, a surface marker used in routine immunophenotyping of AML, may help to predict severe and potentially fatal leukostasis in hyperleukocytic acute myelomonocytic leukaemia. These results emphasize the usefulness of this four-stage clinical grading scale for analysing the factors, which lead to severe leukostasis in hyperleukocytic patients. We extend previous findings that the mechanisms of leukostasis are different depending on the involvement of the monocytic lineage.