© 2020 ISPOR–The Professional Society for Health Economics and Outcomes Research Objectives: Amid a rapid increase in cancer care costs, we examined the extent to which economic evaluations (EEs) were conducted for new treatments evaluated in clinical trials at SWOG, a large National Cancer Institute–sponsored cancer research network. Methods: We investigated phase III cancer treatment clinical trials activated from 1980 onward with primary articles reporting the protocol-designated endpoints published in scientific journals by 2017. Using PubMed, Web of Science, and EconLit, we searched for EEs using trial name, cancer type, information on the comparison arms, and refined keywords for EE designs. We reported the overall proportion of trials with associated EEs and trends of this proportion over time. We synthesized and analyzed information on funding sources, health outcomes, and sources of quality-of-life and cost data from the EEs. Results: Among 182 examined trials, 15 EEs were associated with 13 (7.1%) trials. Among the EEs, almost half (7 of 15) were either unfunded or did not report funding information, whereas nearly half (7 of 15) were funded by pharmaceutical companies and 2 (2 of 15, 13.3%) were supported by federal funding. All EEs reported a healthcare payer perspective. The proportion of trials with an associated EE increased from 1980 to 1989 and 2000 to 2009, but never exceeded 11%. Sources for cost and quality-of-life data for the EEs primarily came from outside the clinical trials. Conclusions: Few economic studies of treatments evaluated in National Cancer Institute–sponsored clinical trials have been conducted. Policymakers, payers, and patients lack economic evidence to consider newly evaluated cancer treatments, despite an urgent need to control healthcare costs.