Circulating Tumor DNA and Risk of Venous Thromboembolism in Locally Advanced Rectal Cancer

Venous thromboembolism (VTE) is a common complication in cancer patients, which negatively affects treatment delivery and, consequently, prognosis. The pathophysiology of cancer‐associated thrombosis (CAT) is extremely complex, relying on cytokine release in response to interactions between tumor cells and macrophages, thus leading to endothelial damage and activation of coagulation. Several risk factors may contribute to VTE risk, including tumor types, advanced stage, and anti-cancer treatments. Anti-angiogenic agents or combination of systemic chemotherapy and concomitant radiotherapy (CT-RT), for instance, are well-established risk factors across different malignancies. Colorectal cancer (CRC) is not listed as a high-risk VTE tumor according to pivotal risk assessment models, although retrospective studies showed a VTE rate of around 20%. Consequently, considering the high prevalence of the disease, VTE in CRC represents a main burden in terms of morbidity, increased healthcare costs, and mortality. Rectal cancer (RC) comprises approximately 30% of all CRC. The treatment of locally advanced disease (LARC) consists of a multimodal approach which includes chemotherapy, radiotherapy, and surgery. In the context of CRC management, circulating tumor DNA (ctDNA) is a fast-growing tool able to detect minimal residual disease, useful for improving patients' stratification and prognosis. Moreover, its determination at the time of diagnosis may represent a surrogate of tumor burden, potentially increasing the risk of VTE compared to ctDNA negative patients. Due to the paucity of prospective data of VTE in LARC, the aim of this analysis is to describe the rate of VTE and the potential association between ctDNA levels at baseline and VTE occurrence. We conducted a prospective observational study enrolling patients with LARC managed with neoadjuvant CT-RT (capecitabine 1650 mg/m2 concomitant with 50,4 Gy pelvic long course radiotherapy), surgery, plus/minus adjuvant chemotherapy at European Institute of Oncology (IEO) between November 2014 and November 2019. Blood samples for ctDNA were obtained at pre-planned timepoints: baseline (T0), end of CT-RT (T1), after surgery (T2), end of adjuvant chemotherapy (T3). ctDNA was extracted from plasma and mutations detected on tumor biopsy (KRAS, NRAS, BRAF, PIK3CA) were evaluated on ctDNA. Among other clinical information, VTE events were collected, including pulmonary embolism (PE), deep vein thrombosis (DVT) and visceral v