Clinical correlates of in vitro effect of methotrexate on acute leukemia blasts.

suppression. The lymphoblasts of children were more sensitive to MTX than were the lymphoblasts of adults. When patients with acute lymphoblastic leukemia were put into remission and maintained with MTX, there was a correlation between sensitivity to MTX in vitro and length of remission. There was also a correlation between in vitro effect of MTX and duration of survival, and the correlation was better than that between blast count and survival. Surprisingly, in patients with nonlymphoblastic leukemia there was also a good correlation between initial sensitivity to MTX in vitro and duration of survival despite the fact that most of these patients were never treated with MTX. In this group, the blast count did not correlate with survival. The suppression of tritiated thymidine incorporation could not be prevented by simultaneous addition of purines or reversed by delayed addition of folinic acid, suggesting that the suppressive effect was due to rapid in vitro kill of leukemic blasts.