The hematologic change during the treatment of acute lymphoblastic leukemia(ALL) is critical as a prognostic determinant and a variable to determine the dose of chemotherapeutic agents. It is known that the dose of vincristine used in the maintenance phase of ALL is small enough to increase the count of platelet. To investigate the change of platelet count according to the vincristine administration in maintenance phase of ALL chemotherapy, we performed this study.

Eleven patients eligible under the criteria of Children's Cancer Study Group(CCG)-1882 and who had completed chemotherapy were enrolled in this study. The count of platelets before vincristine administration was compared with those of vincristine administration 1, 2 and 3 weeks after the early and last periods of maintenance phases. The platelet count before vincristine administration was defined as 100 percent and that after vincristine were compared. In addition, we tentatively defined an enhancing effect of vincristine as positive when the relative count was more than 120 percent.

Platelet count did not differ according to the early and last periods of maintenance phase. Platelet count at first week after vincristine administration increased more significantly than that before vincristine in early and last periods. There was an enhancing effect in 10(90.9 percent) of 11 patients after 1 week vincristine administration both in the early and last periods of the maintenance phase.

Vincristine, used in ALL maintenance phases as a low dose, increased platelet count 1 week after administration. The increased platelet count resumed to the previous level 2-3 weeks later. However, the thrombocytosis observed in the maintenance phase by vincristine was not high enough to induce thrombosis. In addition, vincristine is known to reduce the activity of platelets. Therefore, the risk of thrombosis in the maintenance phase of ALL chemotherapy would be low.