BackgroundNational-level data of cancer patients' readmissions after ST-segment elevation myocardial infarction (STEMI) are lacking. ObjectivesThe primary aim of this study was to compare the rates and causes of 30-day readmissions in patients with and without cancer. MethodsAmong patients admitted with STEMI in the United States National Readmission Database (NRD) from October 2015–December 2017, we identified patients with the diagnosis of active breast, colorectal, lung, or prostate cancer. The primary endpoint was the 30-day unplanned readmission rate. Secondary endpoints included in-hospital outcomes during the index admission and causes of readmissions. A propensity score model was used to compare the outcomes of patients with and without cancer. ResultsA total of 385,522 patients were included in the analysis: 5956 with cancer and 379,566 without cancer. After propensity score matching, 23,880 patients were compared (Cancer = 5949, No Cancer = 17,931). Patients with cancer had higher 30-day readmission rates (19% vs. 14%, p < 0.01). The most common causes for readmission among patients with cancer were cardiac (31%), infectious (21%), oncologic (17%), respiratory (4%), stroke (4%), and renal (3%). During the first readmission, patients with cancer had higher adjusted rates of in-hospital mortality (15% vs. 7%; p < 0.01) and bleeding complications (31% vs. 21%; p < 0.01), compared to the non-cancer group. In addition, cancer (OR 1.5, 95% CI 1.2–1.6, p < 0.01) was an independent predictor for 30-day readmission. ConclusionsAbout one in five cancer patients presenting with STEMI will be readmitted within 30 days. Cardiac causes predominated the reason for 30-day readmissions in patients with cancer.