Non-O blood type linked to higher VTE risk in cancer patients

Non-O blood type appears to be a risk factor for cancer-associated venous thromboembolism (VTE), particularly in patients who have cancer types with low to intermediate thrombotic risk, according to data from the Cancer and Thrombosis Study (CATS) presented at ASH 2021.

“Non-O blood type is associated with higher levels of factor FVIII activity and von Willebrand factor compared with blood type O, and has been identified as a risk factor for VTE in the general population,” explained the researchers.

Given that VTE is a common occurrence in cancer patients, the researchers sought to understand if the association between non-O blood type and VTE extends to cancer patients as well.

In the prospective observational CATS, 1,708 patients (median age 61 years, 46 percent female) with newly diagnosed or recurrent cancer in Vienna were followed for up to 2 years on occurrence of VTE. The most common type of cancers included lung (19 percent), breast (16 percent), and brain (14 percent) cancer — with 32 percent of solid tumour cases already at metastatic stage. In terms of blood type, 38 percent of patients were of blood type O, 40 percent were type A, and 7 percent were type AB. [ASH 2021, abstract 2119]

During 24 months of median follow-up, VTE was detected in 151 patients (cumulative incidence, 9.2 percent, 95 percent confidence interval [CI], 7.9–10.7) while 649 patients had died (2-year mortality rate, 38 percent).

The researchers found that non-O blood type appeared to be associated with an increased risk of VTE in a time-dependent manner. The cumulative incidence of VTE in patients with blood type O vs non-O type was 3.8 percent vs 3.4 percent at 3 months. The difference between type O and non-O grew larger over time, with cumulative VTE incidence of 5.7 percent vs 6.5 percent at 6 months, 7.0 percent vs 8.4 percent at 12 months, and 7.6 percent vs 10.2 percent at 24 months, respectively (Gray´s test, p=0.103).

Based on time-restricted regression modelling, there was no difference in VTE risk between patients with non-O vs O blood type during the initial 3 months of follow-up (hazard ratio [HR], 1.00; p=0.992). Beyond the first 3 months, non-O blood type was associated with a greater risk of VTE compared with blood type O (HR, 1.79; p=0.015).

“Non-O blood type was identified as a time dependent risk factor for cancer-associated VTE,” the researchers reported. “Beyond the first 3 months of follow-up, an increased VTE-risk in non-O blood types was observed, comparably in magnitude to the risk difference in the general non-cancer population.”

Furthermore, the association between non-O blood type and increased VTE risk persisted even when the analysis was restricted to patients with cancer types with low or intermediate thrombotic risk (HR, 1.73; p=0.019). By contrast, no such association was seen in patients with very high risk cancer types, such as glioblastoma, pancreatic, and gastric cancer (HR, 0.94; p=0.824).

“These findings indicate non-O blood type as a putative risk factor for VTE in patients with cancer in comparably low thrombotic risk scenarios,” said the researchers.