Vincristine and Platelet Function

To the Editor.— In their article on the "Treatment of Thrombotic Thrombocytopenic Purpura With Vincristine" (1982;247:1433), Gutterman and Stevenson attribute the possible beneficial effect of the drug to its effect on the endothelial cells.1They consider the vincristine sulfate treatment aside from agents that inhibit platelet aggregation, and state that the effect ofVincaalkaloids on platelets has not been defined. Vincaalkaloids dissolve microtubules and impair the particular cell function with which these structures appear to be associated. When platelets are incubated in vitro withVincaalkaloids, the microtubules are disrupted, the discoid platelet becomes relatively spherical,2and interference with normal aggregation occurs.3We have demonstrated in vivo that a large percentage of patients receiving vincristine have a demonstrable thrombocytopathy with absent second-phase platelet aggregation to epinephrine and adenosine diphosphate (ADP).4Therefore, the possible therapeutic effect of vincristine in thrombotic thrombocytopenic purpura (TTP) may be