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Background andAims: Angiotensin converting enzyme inhibitors (ACE-I) and angiotensin IItype I receptor (AT1R) antagonists are commonly used as a treatment forhypertension. Recent experimental and population studies have suggested thatthese agents may exert an inhibitory effect on malignancy, possibly throughanti-angiogenic pathways. The aim of this study was to investigate the effectof an ACE-I (captopril) and an AT1R antagonist (irbesartan) in colorectalcancer liver metastases.Methods: The effect ofcaptopril and irbesartan on tumor growth was investigated in a mouse modelusing quantitative stereological and histological analysis. Tumormicrocirculation was assessed by microvascular resin casting. A survival studywas also carried out.Results: Bothcaptopril and irbesartan markedly decreased tumor growth when compared tocontrol (P = 0.003 and P = 0.004, respectively).However, there was no significant difference in survival or tumor necrosis foreither of the drugs. Tumor microvasculature exhibited a reduction in centralmicrovascular density, with constriction and tapering of vessels.Conclusion: Captopriland irbesartan caused a marked reduction in volume of colorectal cancer livermetastases and caused changes in tumor microvasculature. However, there was nodifference in percentage tumor necrosis or improvements in survival. Furtherinvestigation is needed to identify the mode of action of these agents. Leggil'articolo