The relationship between the in vitro chemosensitivity of tumor cells and tumor response in vivo in an experimental tumor model

Cell lines derived from a panel of five histologically distinct murine adenocarcinomas of the colon (MAC) were used to assess whether or not a colony‐forming ambucil (CHL). The preddictive value of the clonogenic assay was significantly improved ance curves;) were used to determine clonogentic cell kill in vitro, instead of one‐tenth peak plasma drug comcentration and total plasma drug AUC exposures. Despite the good correlation between in vitor and in vivo responses observed, the clonogenic assay could not forecast the site‐dependent response of MAC 15A to CHL. These site‐dependent responses cannot be explained in terms of the inberent sensitivity of tumor cells themseelves, suggesting that caution must be applied in the interpretation of in vitor chemosensitivity assays.