Importance: Drugs are used in the adjuvant, metastatic, or both settings in cancer, but the rate, direction, and speed with which drugs are tested and indicated in each setting are unknown. Objective: To identify the number of unique agents that are currently category 1 or 2A per National Comprehensive Cancer Network (NCCN) guidelines in metastatic and adjuvant settings of non-small cell lung cancer (NSCLC), breast cancer, and colon cancer, as well as the mean delay between use in these 2 settings and the quality of supporting evidence. Design, Setting, and Participants: This cross-sectional study used NCCN treatment guidelines current as of May 15, 2019, and the clinical trials cited either by these guidelines or within corresponding drug labels. Trials published between 1970 and 2019 were evaluated. The analysis included published clinical trials of systemic therapy options deemed by the NCCN as category 1 or 2A. Participants included patients with early or metastatic NSCLC, breast cancer, or colon cancer who were included in clinical trials evaluating current NCCN-recommended systemic therapy options. Data analysis was performed from March 2019 to May 2019. Exposures: Systemic therapy regimens used as either adjuvant treatment or as therapy for metastatic disease in the 3 cancer types. Main Outcomes and Measures: Number of agents recommended for use in adjuvant and metastatic settings of NSCLC, colon cancer, and breast cancer, the mean delay between use in these 2 settings, and the percentage of agents supported by trials with substantial improvement in either progression-free survival (disease-free survival for adjuvant agents) or overall survival. Results: This study identified 69 agents recommended for use in metastatic disease compared with 25 agents recommended for adjuvant use. For agents used in both settings, the mean (SD) delay between use in metastatic disease and as adjuvant therapy was 10.0 (7.5) years. On the basis of trials with positive outcomes, 39 of 69 agents (56.5%) were approved or recommended in the metastatic setting, compared with 23 of 25 agents (92.0%) approved for use as adjuvant therapy. Conclusions and Relevance: There is a substantial difference in the number of agents available for use, as well as the timing of supporting evidence, in the metastatic and adjuvant settings for NSCLC, breast cancer, and colon cancer. Given the potential benefit of adjuvant therapy in these cancer types, further investigation into additional adjuvant systemic therapy options is warranted..
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