A model yielding the probability of curative outcome for a patient at the time of tumor detection is presented. The status of the patient is determined by whether or not metastases (distant spread of the tumor) have occurred and whether any such metastases are drug resistant. If there are no metastases, then local excision is presumed curative; if there are nonresistant metastases, then local excision plus adjuvant chemotherapy is presumed curative; if any metastases are drug resistant, there is no cure. Metastases and drug resistance arise independently with intensities proportional to total tumor size. Over a wide range of such intensities, the addition of adjuvant drug therapy yields a dramatic improvement in the probability of cure.