PURPOSE Delays and disruptions in health systems because of the COVID-19 pandemic were identified by a previous systematic review from our group. For improving the knowledge about the pandemic consequences for cancer care, this article aims to identify the effects of mitigation strategies developed to reduce the impact of such delays and disruptions. METHODS Systematic review with a comprehensive search including formal databases, cancer and COVID-19 data sources, gray literature, and manual search. We considered clinical trials, observational longitudinal studies, cross-sectional studies, before-and-after studies, case series, and case studies. The selection, data extraction, and methodological assessment were performed by two independent reviewers. The methodological quality of the included studies was assessed by specific tools. The mitigation strategies identified were described in detail and their effects were summarized narratively. RESULTS Of 6,692 references reviewed, 28 were deemed eligible, and 9 studies with low to moderate methodological quality were included. Five multiple strategies and four single strategies were reported, and the possible effects of mitigating delays and disruptions in cancer care because of COVID-19 are inconsistent. The only comparative study reported a 48.7% reduction observed in the number of outpatient visits to the hospital accompanied by a small reduction in imaging and an improvement in radiation treatments after the implementation of a multiple organizational strategy. CONCLUSION The findings emphasize the infrequency of measuring and reporting mitigation strategies that specifically address patients' outcomes and thus a scarcity of high-quality evidence to inform program development. This review reinforces the need of adopting standardized measurement methods to monitor the impact of the mitigation strategies proposed to reduce the effects of delays and disruptions in cancer health care because of COVID-19.