In vitro sensitivity of xenografts to vincristine and dexamethasone. Xenograft cells were retrieved from cryostorage and cultured for cell survival assays exactly as described in “Materials and methods.” Survival at each drug concentration was expressed relative to solvent-treated controls. Each data point represents the mean ± SEM of at least 3 separate experiments. Xenografts were stratified into good (solid lines, open symbols) or poor (dashed lines, closed symbols) patient outcome subgroups, as defined in Tables 1 and 5, the legend to Figure 3, and in “In vivo responses of xenografts to vincristine, dexamethasone, or methotrexate, and their correlation with clinical outcome.” Symbols representing each xenograft are indicated. Whereas the sensitivity of xenografts to vincristine (A) showed a trend toward stratifying according to patient outcome, there were clearly 2 separate groups of dexamethasone responses (B).