IntroductionCancer patients are prone to infections, but the mortality of fatal infections remains unclear. Understanding the patterns of fatal infections in patients with cancer is imperative. In this study, we report the characteristics, incidence, and predictive risk factors of fatal infections among a population-based cancer cohort.MethodsA total of 8,471,051 patients diagnosed with cancer between 1975 and 2016 were retrospectively identified from the Surveillance, Epidemiology, and End Results (SEER) program. The primary outcome was dying from fatal infections. Mortality rates and standardized mortality ratios (SMRs) adjusted for age, sex, race, and calendar year were calculated to characterize the relative risks of dying from fatal infections and to compare with the general population. Furthermore, cumulative mortality rates and the Cox regression models were applied to identify predictive risk factors of fatal infections.ResultsIn cancer patients, the mortality rate of fatal infections was 260.1/100,000 person-years, nearly three times that of the general population [SMR, 2.92; 95% (confidence interval) CI 2.91–2.94]. Notably, a decreasing trend in mortality rate of fatal infections was observed in recent decades. SMRs of fatal infections were highest in Kaposi sarcoma (SMR, 162.2; 95% CI 159.4–165.1), liver cancer (SMR, 30.9; 95% CI 30.0–31.8), acute lymphocytic leukemia (SMR, 19.1; 95% CI 17.0–21.4), and acute myeloid leukemia (SMR, 13.3; 95% CI 12.4–14.3). Patients aged between 20 and 39 years old exhibited a higher cumulative mortality rate in the first few years after cancer diagnosis, whereas the cumulative mortality rate of those > 80 years old was rapidly increasing and became the highest approximately 3 years post-cancer diagnosis. Predictive risk factors of dying from fatal infections in cancer patients were the age of 20–39 or > 80 years, male sex, black race, diagnosed with cancer before 2000, unmarried status, advanced cancer stage, and not receiving surgery and radiotherapy, but receiving che...