Cancer procoagulant in acute lymphoblastic leukemia.

In a previous study we characterized cancer procoagulant (CP), a 68 kd cysteine proteinase which directly activates coagulation factor X in various subtypes (from M1 to M5) of acute non-lymphoblastic leukemia (ANLL). The aim of this study was to determine whether CP is also expressed by acute lymphoblastic leukemia (ALL) cells. Blasts from 25 ALL patients were extracted and tested for their procoagulant properties. 16 samples (64%) shortened the recalcification time of normal human plasma, and 9 (36%) did not. 8 of the 16 active samples showed properties compatible with CP, i.e. independence from factor VII in triggering blood coagulation and sensitivity to cysteine proteinase inhibitors. Selected samples also cross-reacted with a polyclonal antibody raised against purified CP. The specific activity of CP in ALL extracts was significantly lower than in most ANLL types previously studied (all but M4). These finding indicate that CP can be a property of the lymphoid phenotype although its expression may be lower than in the myeloid phenotype.