Scientific publication is an important tool for knowledge dissemination and career advancement, but authors affiliated with institutions in low- and middle-income countries (LMICs) are historically underrepresented on publications. To assess the country income level distribution of author affiliations for publications resulting from National Cancer Institute (NCI)-supported extramural grants between 2015 and 2019, with international collaborating institutions exclusively in 1 or more LMICs. This cross-sectional study assessed authorship on publications resulting from NCI-funded grants between October 1, 2015, and September 30, 2019. Grants with collaborators in LMICs were identified in the National Institutes of Health (NIH) Query/View/Report and linked to publications using Dimensions for NIH, published between 2011 and 2020. Statistical analysis was performed from May 2021 to July 2022. Author institutional affiliation was used to classify author country and related income level as defined by the World Bank. Relative citation ratio and Altmetric data from Dimensions for NIH were used to compare citation impact measures using the Wilcoxon rank sum test. In this cross-sectional study, 159 grants were awarded to US institutions with collaborators in LMICs, and 5 grants were awarded directly to foreign institutions. These 164 grants resulted in 2428 publications, of which 1242 (51%) did not include any authors affiliated with an institution in an LMIC. In addition, 1884 (78%) and 2009 (83%) publications had a first or last author, respectively, affiliated with a high-income country (HIC). Publications with HIC-affiliated last authors also demonstrated greater citation impact compared with publications with LMIC-affiliated last authors as measured by relative citation ratios and Altmetric Attention Scores; publications with HIC-affiliated first authors also had higher Altmetric Attention Scores. This cross-sectional study suggests that LMIC-affiliated authors were underrepresented on publications resulting from NCI-funded grants involving LMICs. It is critical to promote equitable scientific participation by LMIC institutions in cancer research, including through current and planned programs led by the NCI.