Although they present more than half of all Americans with cancer, the elderly are under-represented on the clinical trials that seek to determine efficacy and toxicity of chemotherapy. For this reason, results of clinical trials may not be applicable to the general population of elderly cancer patients. Nonetheless, physicians need clinical information regarding tile risks and benefits of chemotherapy in this substantial group of patients. I am a medical oncologist who seeks to develop a career at the crossroads oncology and health services research that is focused on determining the risks and benefits of chemotherapy in the general population of elderly cancer patients. In five years, I want to be able to execute a series of epidemiologic studies examining the possible contribution of medical comorbidity to the chemotherapy utilization and outcomes of elderly Americans with cancer. This long-term research agenda requires additional training on my part and three preliminary studies to determine the ability of a candidate data source, Heath Care Financing Administration's Medicare claims files, to provide inexpensive but reliable clinical information for these studies. Through the three related projects, I seek to determine the reliability of Medicare chemotherapy claims at capturing three critical elements of anti-cancer therapy 1) chemotherapy administration, 2) chemotherapy-related toxicities, and 3) disease-free survival. To meet these three aims, I will create a new and unique data set by linking Medicare claims to a gold-standard of clinical information regarding chemotherapy administration and outcomes, Cancer and Leukemia Group B (CALGB) clinical trial data. Defining the CALGB data as the gold standard against which to compare the Medicare claims, I will then calculate the sensitivity and specificity of the Medicare claims at capturing 1) chemotherapy administration, and 2) specific chemotherapy-related toxicities, and 3) disease-free survival. In the next phase of my career, I will use Medicare claims, to the extent of their validity, to execute a series of epidemiologic studies examining the chemotherapy utilization and outcomes of elderly Americans with cancer and medical comorbidity.