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Aims: Cyclo-oxygenases 1 and 2 (COX-1 and COX-2) are key enzymes in prostaglandin biosynthesis. COX-2 is induced by a wide variety of stimuli, and present during inflammation. COX-2 overexpression has been observed in colon, head and neck, lung, prostate, stomach, and breast cancer. In colon and gastric cancer, COX-2 expression was associated with angiogenesis. The aim of this study was to determine the relation between COX-2 expression and angiogenesis in breast cancer, and to correlate the expression of this enzyme with classic clinicopathological parameters.
Methods: COX-2 expression was investigated by immunohistochemistry and western blotting analysis. The expression of COX-2 was then related to age, histological grade, nodal status, oestrogen receptor status, p53 expression, c-erb-B2 overexpression, mitotic counts, MIB-1 labelling index, apoptotic index, sialyl-Tn expression, transforming growth factor [alpha] expression, microvessel density, and disease free survival in 46 patients with invasive ductal breast carcinoma.
Results: By means of immunohistochemistry, COX-2 expression was detected in eight of the 46 carcinomas studied. Western blotting showed COX-2 protein expression in the same breast tumours, but not in normal adjacent tissues. The density of microvessels immunostained with anti-F-VIII related antigen was significantly higher in patients with COX-2 expression than in those without expression (p = 0.03). In addition, COX-2 was significantly associated with the presence of sialyl-Tn expression (p = 0.02), lymph node metastasis (p = 0.03), a high apoptotic index (p = 0.03), and a short disease free survival (p = 0.03) in univariate analyses.
Conclusions: These data suggest that COX-2 expression is associated with angiogenesis, lymph node metastasis, and apoptosis in human breast cancer. Moreover, these results warrant further studies with larger series of patients to confirm the association with short disease free survival in patients with breast cancer.
Arachidonic acid metabolites, such as prostaglandins, thromboxanes, and various lipoxygenase products, are produced in many tissues and are responsible for a wide variety of biological responses. They are potent mediators, affecting several signal transduction pathways that modulate cellular adhesion, growth, and differentiation. (1 2)
Cyclo-oxygenase (COX) (otherwise known as prostaglandin endoperoxide synthase) catalyses the conversion of arachidonic acid to prostaglandin endoperoxide (prostaglandin [H.sub.2]). This is the rate limiting step in prostaglandin and thromboxane biosynthesis. Two isoforms of prostaglandin synthase have been identified and are often referred to as COX-l and COX-2. (3) COX-1 is constitutively expressed in most tissues and is thought to be involved in maintaining cellular homeostasis. (4) In contrast, COX-2 is frequently undetectable at baseline in normal tissues, but can undergo rapid induction in response to a variety of stimuli, including mitogens, hormones, cytokines, and growth factors. The effects of both cyclo-oxygenases are mediated via tyrosine kinase, protein kinase C, and/or protein kinase A signal transduction pathways. (5)
Overexpression of COX-2 and high concentrations of prostaglandins have been associated with chronic inflammatory diseases, such as rheumatoid arthritis, (6 7) and several types of human cancer, including colon, head and neck, lung, bladder, prostate, stomach, and breast cancer. (8-18) During cancer progression, prostaglandins can mediate several mechanisms, including cell proliferation, (19) apoptosis, (20 21) modulation of the immune system, (22 23) and angiogenesis. (24 25) Angiogenesis or neovascularisation, is the formation of new blood vessels from pre-existing ones. (26 27) In physiological processes, angiogenesis plays an important role in the female reproductive cycle (ovulation, menstruation) and in tissue growth and repair. In chronic inflammatory diseases, the formation of new blood vessels maintain the inflammatory state, by transporting inflammatory cells and supplying oxygen and nutrients to the proliferative inflamed tissue. (28)
During tumorigenesis, angiogenesis is important for tumour growth and metastasis. Any increase in a tumour mass must be preceded by an increase in the vascular supply, to deliver nutrients and oxygen to the tumour. Angiogenesis is mediated by a change in the local equilibrium between positive and negative angiogenic factors. Among the most important proangiogenic factors are vascular endothelial growth factor (VEGF), fibroblast growth factor, platelet derived growth factor, and angiopoietin 1. (26 27)
Although the mechanisms underlying the contribution of COX-2 to tumorigenesis are still unclear, an association between COX-2 overexpression and angiogenesis has been demonstrated in two types of cancer--colorectal and gastric cancer. (23 24) Overexpression of COX-2 in a colorectal cancer cell line was shown to stimulate the production of angiogenic factors, such as VEGF. (24) In a recent study, COX-2 expression was associated with increased angiogenesis in gastric cancer. (25)
Increased concentrations of prostaglandins [E.sub.2'] a major product of COX-2, have been reported in …