Ording A.G., Horváth-Puhó E., Lash T.L., Ehrenstein V., Borre M., Vyberg M., Sørensen H.T.
BACKGROUND: Venous thromboembolism (VTE) is a serious complication of cancer. It is unknown whether comorbidity interacts clinically with prostate cancer (PC) to increase the VTE rate beyond that explained by PC and comorbidity alone, for example, by delaying diagnosis or precluding treatment. METHODS: A nationwide, registry-based cohort study of all 44,035 Danish patients diagnosed with PC from 1995 to 2011 and 213,810 men from the general population matched 5:1 on age, calendar time, and comorbidities. The authors calculated VTE rate ratios and the interaction contrast as a measure on the additive scale of the excess VTE rate explained by synergy between PC and comorbidity. RESULTS: In total, 849 patients in the PC cohort and 2360 men from the general population had VTE during 5 years of follow-up, and their risk of VTE was 2.2% and 1.3%, respectively. The 1-year VTE standardized rate among PC patients who had high comorbidity levels was 15 per 1000 person-years (PYs) (95% confidence interval, 6.8-24 per 1000 PYs), and 29% of that rate was explained by an interaction between PC and comorbidity. The VTE risk was increased among older patients, those with metastases, those with high Gleason scores, those in the D’Amico high-risk group, and those who underwent surgery. CONCLUSIONS: PC interacted clinically with high comorbidity levels and increased the VTE rate. Because of the large PC burden, reducing VTEs associated with comorbidities may have an impact on VTE risk and the potential to improve prognosis. Clinical interactions between high levels of comorbidity and PC on the risk of VTE were observed. Almost 30% of all episodes of VTE occurred among patients who had high levels of comorbidity.