Cell surface expression of lysosome-associated membrane protein-2 (lamp2) and CD63 as markers of in vivo platelet activation in malignancy.

Platelets may become activated in vivo in a number of prethrombotic conditions including cancer. In the present study, cell surface expression of lysosome-associated membrane protein-2 (lamp2) and CD63 (lamp3) were examined by flow cytometry in 15 healthy volunteers and 5 patients with metastatic cancer to determine their utility as markers of in vivo platelet activation. Unstimulated platelets from controls had low levels of lamp2 expression, in contrast to cancer patients, who had significantly elevated levels (3.79 +/- 1.48% vs 33.9 +/- 5.6%). Upon stimulation with collagen, a greater than two-fold increase in the number of platelets expressing detectable levels of lamp2 was seen only among controls and not in cancer patients. Stimulation with collagen also resulted in a nearly two-fold increase in the proportion of platelets expressing CD63 in the control group, and a less than 1.5-fold increase in CD63 was seen in the patient group. The results suggest that cell surface lamp2 and CD63, like cell surface expression of GMP-140, may be good indicators of in vivo platelet activation and may be potentially useful in identifying patients with prethrombotic disorders.