Which cancer treatment agent is most associated with the development of hypertension?

Bevacizumab is a monoclonal antibody that targets vascular endothelial growth factor (VEGF). Its primary mechanism involves inhibiting angiogenesis, the process by which new blood vessels form from existing ones, which is essential for tumor growth and metastasis. While effective for treating various cancers, including colorectal, lung, and breast cancers, one of the notable side effects associated with bevacizumab is hypertension.

The development of hypertension with bevacizumab is thought to occur due to the drug's interference with vascular function. Inhibition of VEGF can lead to a reduction in nitric oxide availability, a crucial factor in vascular homeostasis and endothelial function, potentially resulting in increased vascular resistance and elevated blood pressure.

In contrast, other agents listed, such as fluorouracil, leucovorin, and oxaliplatin, do not carry a significant association with the development of hypertension as a common side effect. While they may produce various other adverse effects, hypertension is particularly notable with bevacizumab, making it the correct answer in this context.