Risk of Venous Thromboembolic Events After Surgery for Cancer.

Importance: The risks and benefits of thromboprophylaxis therapy after cancer surgery are debated. Studies that determine thrombosis risk after cancer surgery with high accuracy are needed. Objectives: To evaluate 1-year risk of venous thromboembolic events after major cancer surgery and how these events vary over time. Design, Setting, and Participants: This register-based retrospective observational matched cohort study included data on the full population of Sweden between 1998 and 2016. All patients who underwent major surgery for cancer of the bladder, breast, colon or rectum, gynecologic organs, kidney and upper urothelial tract, lung, prostate, or gastroesophageal tract were matched in a 1:10 ratio with cancer-free members of the general population on year of birth, sex, and county of residence. Data were analyzed from February 13 to December 5, 2023. Exposure: Major surgery for cancer. Main Outcomes and Measures: The main outcome was incidence of venous thromboembolic events within 1 year after the surgery. Crude absolute risks and risk differences of events within 1 year and adjusted time-dependent cause-specific hazard ratios (HRs) of postdischarge events were calculated. Results: A total of 432 218 patients with cancer (median age, 67 years [IQR, 58-75 years]; 68.7% women) and 4 009 343 cancer-free comparators (median age, 66 years [IQR, 57-74 years]; 69.3% women) were included in the study. The crude 1-year cumulative risk of pulmonary embolism was higher among the cancer surgery population for all cancers, with the following absolute risk differences: for bladder cancer, 2.69 percentage points (95% CI, 2.33-3.05 percentage points); for breast cancer, 0.59 percentage points (95% CI 0.55-0.63 percentage points); for colorectal cancer, 1.57 percentage points (95% CI, 1.50-1.65 percentage points); for gynecologic organ cancer, 1.32 percentage points (95% CI, 1.22-1.41 percentage points); for kidney and upper urinary tract cancer, 1.38 percentage points (95% CI, 1.21-1.55 percentage points); for lung cancer, 2.61 percentage points (95% CI, 2.34-2.89 percentage points); for gastroesophageal cancer, 2.13 percentage points (95% CI, 1.89-2.38 percentage points); and for prostate cancer, 0.57 percentage points (95% CI, 0.49-0.66 percentage points). The cause-specific HR of pulmonary embolism comparing patients who underwent cancer surgery with matched comparators peaked just after discharge and generally plateaued 60 to 90 days later. At 30 days after surgery, the HR was 10 to 30 times higher than in the comparison cohort for all cancers except breast cancer (colorectal cancer: HR, 9.18 [95% CI, 8.03-10.50]; lung cancer: HR, 25.66 [95% CI, 17.41-37.84]; breast cancer: HR, 5.18 [95% CI, 4.45-6.05]). The hazards subsided but never reached the level of the comparison cohort except for prostate cancer. Similar results were observed for deep vein thrombosis. Conclusions and Relevance: This cohort study found an increased rate of venous thromboembolism associated with cancer surgery. The risk persisted for about 2 to 4 months postoperatively but varied between cancer types. The increased rate is likely explained by the underlying cancer disease and adjuvant treatments. The results highlight the need for individualized venous thromboembolism risk evaluation and prophylaxis regimens for patients undergoing different surgery for different cancers.