Over the past several decades, there has been burgeoning interest and investment in large transdisciplinary (TD) team science initiatives that aim to address complex societal problems. Despite this trend, TD training opportunities in the health sciences remain limited, and evaluations of these opportunities are even more uncommon due to funding constraints. We had the unique opportunity to conduct an exploratory study to examine the potential outcomes and impacts of TD training in a National Cancer Institute-supported initiative for TD research and training-the Transdisciplinary Research on Energetics and Cancer I (TREC I) initiative. This study used a retrospective mixed-methods approach leveraging secondary analysis of existing data sources to learn about TREC trainees' experiences with TREC training, TD research competencies, changes in scholarly productivity, and the associations among these domains. Results indicated that, on average, TREC trainees were satisfied with their TREC mentoring experiences and believed that TREC training processes were effective, in general. Participation in TREC training was associated with TD research competencies, including TD research orientation, positive general attitude toward TD training, development of scientific skills for TD research, and intrapersonal/interpersonal competencies for collaboration. There was also a significant increase in trainees' scholarly productivity from before to after starting in TREC training, as indicated by average annual number of publications and presentations and average number of coauthors per publication. Perceived effectiveness of TREC training was positively correlated with change in average annual number of research presentations from before to after starting in TREC training (r = 0.65, p < 0.05, N = 12), as well as TD research orientation (r = 0.36, p < 0.05), general attitude toward TD training (0.39, p < 0.05), scientific skills for TD research (r = 0.45-0.48, p < 0.05), and perceived collaborative productivity at one's TREC center (r = 0.47, p < 0.01). Finally, a significant positive correlation was observed between multi-mentoring experiences and both TD research orientation (r = 0.58, p < 0.05) and perceived collaborative productivity at one's TREC center (r = 0.44, p < 0.05). This exploratory study had methodological constraints including the absence of a comparison group and cross-sectional rather than longitudinal data related to TD research competencies. Despite these limitations, the study provided an opportunity to use existing data sources to explore potential outcomes and impacts of TD training and inform development of future rigorous evaluations of TD training. Overall, findings suggest that TD training in the context of a TD research initiative can provide satisfying training opportunities that support the development of TD research competencies and promote scholarly productivity.