Risk Score For Venous Thromboembolism (VTE) In Ambulatory Patients: Impact Of Cancer Type and Risk Score On VTE Incidence, Early Mortality and Progression-Free Survival

While ambulatory patients receiving cancer chemotherapy are at increased risk for venous thromboembolism (VTE), current guidelines do not recommend routine thromboprophylaxis with a few notable exceptions (Lyman, Khorana et al, J Clin Oncol 2013). A previously validated VTE risk score for cancer outpatients stratifies patients into low (0), intermediate (1-2), or high (>=3) risk categories (Khorana, Kuderer et al, Blood 2008). Understanding cancer types at greatest risk for VTE as well as early mortality and progression based on the risk score provides key clinical understanding.

A prospective cohort study was conducted of consenting solid tumor and lymphoma patients initiating a new chemotherapy regimen at 115 randomly selected US oncology practices between 2002 – 2006 by the ANC Study Group. VTE incidence, progression-free survival (PFS), and all-cause mortality over the first 120 days (early mortality) of ambulatory chemotherapy were estimated based on the method of Kaplan and Meier.

Among 4,458 patients initiating a new chemotherapy regimen, 93 (2.1%) developed a symptomatic VTE within 120 days of chemotherapy. The risk of VTE across cancer types increased from 0.6%, to 1.8% to 6.6% in low-, intermediate- and high-risk categories, respectively. The risk of VTE among low risk patients was 1% or less across all cancer types. However, the risk of VTE was highest among intermediate- and high-risk categories in patients with breast, colorectal, and lung cancer, reaching 16% for high risk breast cancer patients. Early all-cause mortality occurred in 136 patients (3.1%) and also increased with increasing risk score from 0.8% to 3.4% to 6.4% in low-, intermediate- and high-risk categories, respectively. The risk of early mortality was 2.1% or less in low risk patients across all cancer types. However, the risk of early mortality was highest among high-risk category patients, reaching 23% and 14% in colorectal cancer patients and pancreatic or gastric cancer patients, respectively. PFS decreased from 92% to 82% to 72% across the three risk categories, with lowest rates of PFS among colorectal (52%) and lung cancer (52%) patients.

VTE incidence and all-cause mortality increase and PFS correspondingly decreases with increasing VTE risk score across major solid tumors. Interestingly, while breast cancer is not considered a high risk tumor for VTE, breast cancer patients with a risk score of >=3 had the highest VTE incidence compared to other major solid tumor types. Among patients with a risk score of >=3, gastrointestinal cancer patients had the greatest risk of early mortality and correspondingly, the lowest PFS compared to other major solid tumors. These findings also suggest that both the mortality risk as well as the VTE risk are only partially influenced by tumor type.

Funding: 1KM1-CA156687-01 (NK), ASCO Young Investigator Award (NK), NHLBI-1R01HL095109 (all), ANC Study Group (GL), and K23 CA120587 (AK).

No relevant conflicts of interest to declare.