With a direct in vitro tumor-colony assay developed to measure sensitivity of human-tumor stem cells to anticancer drugs, we performed 32 retrospective or prospective clinical studies in nine patients with myeloma and nine with ovarian cancer treated with standard agents that were tested in vitro. The results were clearly correlated (P<0.00001). Unique patterns of sensitivity and resistance to the six drugs tested were observed for individual patients. In eight cases of myeloma and three of ovarian carcinoma in vitro sensitivity corresponded with in vivo sensitivity whereas in one case of myeloma it did not. In vitro resistance correlated with clinical resistance in all five comparisons in myeloma and all 15 in ovarian cancer. We conclude that this assay shows sufficient promise to warrant larger-scale testing to determine its efficacy for selection of new agents and individualized cancer chemotherapy regimens. (N Engl J Med 298:1321–1327, 1978) CANCER chemotherapy has improved substantially within the past decade. However, selection of effective chemotherapy for individual patients remains somewhat of a trial-and-error procedure. Predictive technics (similar to the culture and sensitivity assays used for the management of microbial infections) have not been available. Numerous clinical observations have shown a wide range of responsiveness to particular treatments among patients with cancers of identical histopathologic type. Such individual differences in responsiveness have been particularly well documented in the monoclonal neoplasm multiple myeloma, for which tumor burden and response can be quantitated.1 2 3 Investigators at the Ontario Cancer Institute showed that tumor stem cells.
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