Background: To investigated the prognosis of the most prevalent cancers (breast-, gastrointestinal-, and lung cancer), according to cancer status (i.e., active-, non-active-, history of-, and no cancer), following first-time of acute coronary syndrome (ACS). Methods: Danish nationwide registers were used to identify patients with first-time ACS from 2000−2018. Patients were stratified according to cancer type and status. Hazard ratios (HR) estimated by adjusted Cox regression models for 1year all-cause mortality reported. Further absolute risks of 1year cardiovascular versus non-cardiovascular death and 30-day cumulative incidence of coronary angiograms (CAG) was estimated, using the Aalen-Johansen non-parametric method, with competing risk of death. Results: We identified 150,478 (95.7%) with no cancer, 2,370 (1.5%) with history of cancer, 2,712 (1.7%) with non-active cancer and 1,704 (1.1%) with active cancer. Cancer patients were older with more comorbidities than patients with no cancer. When compared with no cancer, we found HRs (95% confidence intervals) of 1.71 (1.44−2.02), 2.47 (2.23−2.73) and 4.22 (3.87−4.60) correspondingly for active breast-, gastrointestinal-, and lung cancer. Increased HRs were also found for non-active cancers, but not for history of cancer. Cardiovascular disease was the leading cause of death in all patients. Among patients with active breast-, gastrointestinal-, and lung cancer 43%, 43%, and 31% underwent CAG, correspondingly, compared with 77% of patients without cancer. Conclusions: Active- and non-active cancers were associated with an increased 1-year all-cause mortality compared with patients with history of cancer and no cancer. Cardiovascular disease was the leading cause of death; notably CAG was less frequently performed in cancer patients.