Although gene therapy and immunotherapy hold great promise for the future, cancer treatment now centers around surgical resection, radiation therapy, and chemotherapy. The therapeutic basis of surgical resection is obvious, but the same cannot be said for the other approaches. What accounts for the selective killing of malignant cells while normal cells are spared? It is clearly not simple differences in rates of replication. Why do cancers even of the same histologic type vary in their sensitivity to chemotherapy and radiotherapy? What accounts for the frustrating development of drug resistance? Recent findings provide a possible link between these questions and . . .