Venous thromboembolism (VTE) is associated with an increased prevalence of occult cancer. As pregnancy is also associated with an increased risk of VTE, it is unknown whether VTE during pregnancy or the postpartum period is similarly associated with an increased risk of a subsequent malignancy.
Anette Tarp Hansen, PhD, of the Department of Clinical Epidemiology at Aarhus University Hospital in Denmark, and co-authors conducted a, nationwide study of nearly 4,000 pregnant women who developed VTE and found that VTE occurrence during pregnancy or postpartum appeared to be a marker of an underlying occult cancer.
"[Our study] showed that the risk of having a diagnosis of malignancy in the first year after a VTE episode during pregnancy or the postpartum period was higher than expected compared with the general female population of the same age and in [the] same calendar years," the authors wrote of the findings, which were published in Blood Advances.
The researchers used several national Danish databases to identify women without cancer who developed VTE (both incident and recurring VTE, including deep VTE and superficial venous thrombosis) during pregnancy or the 12 weeks after delivery. They also assessed incidence of occult cancer.
The authors identified any VTE risk factors (including obesity, smoking, surgery, fracture, trauma, cesarean section, and postpartum bleeding) and comorbid conditions (including diabetes, chronic rheumatologic disease, and inflammatory disease) related to an increased risk of cancer.
The study included women with VTE during pregnancy or the postpartum period who delivered a child between January 1, 1978, and November 20, 2013. Patients were followed until cancer diagnosis, death, emigration, or cutoff date (November 30, 2013), and cancer incidence was assessed at three timepoints after VTE diagnosis (<6 months, 6-12 months, and 1 year). Outcomes were stratified based on patient age, obesity at the time of VTE diagnosis, and timing of the event (antepartum or postpartum).
During a median follow-up of 14.8 years (range = 6.7-24.2 years), 3,934 women were diagnosed with VTE during pregnancy or postpartum, 8.8 percent of whom had a prior history of VTE. A total of 250 women were subsequently diagnosed with cancer: 64 (25%) after VTE during pregnancy and 186 (75%) after VTE during the postpartum period.
"The number of cancer cases observed within six months after a VTE event was higher than expected (absolute risk = 0.10%; 95% CI 0.04-0.25; standardized incidence ratio [SIR] = 1.77; 95% CI 0.48-4.53), especially after a postpartum VTE event (SIR=2.86; 95% CI 0.78-7.33)," the authors wrote. The increased risk remained during the six to 12 months after VTE (SIR=3.27; 95% CI 0.67-9.56), and cancer risk was still moderately increased after one year (SIR=1.23; 95% CI 0.94-1.58). The risk returned to "expected levels" during the remaining follow-up (absolute risk = 20.13%; 95% CI 16.55-23.98), according to the authors. See TABLE for more outcomes.
"The risk of having a cancer diagnosed within the first months after a VTE episode in relation to pregnancy seems increased," the authors concluded.
The study is limited by its retrospective design. In addition, the data during the first year of follow-up were "sparse, yielding imprecise risk estimates for site-specific cancers," the authors noted.
The Lundbeck Foundation and Novo Nordisk Foundation provided financial support for the study.
The authors report no financial conflicts.
Hansen AT, Veres K, HorvÃ¡th-PuhÃ³ E, et al. Pregnancy-related venous thromboembolism and risk of occult cancer. Blood Advances. 2017 October 24.