Requesting a second opinion to advise about diagnosis, treatment, or prognosis has implications for patient safety. This systematic review examined the prevalence and outcomes of patients with cancer who obtained a second opinion. Researchers included studies that demonstrated varying estimates of second opinion rates, which could be as high as one-third of all cases. The prevalence of changes in diagnosis, treatment recommendations, and prognosis based on a second opinion also differed widely, as found in a prior systemic review. Patient satisfaction with second opinions was consistently high. The authors note the lack of relevant patient outcomes or standardized quality metrics across all included studies of second opinions. They recommend a structured and transparent second opinion process as part of oncologic care. A WebM&M commentary described a change in diagnosis following a second opinion.