The cyclooxygenase (COX) enzymes catalyse the rate-limiting step of conversion from arachidonic acid to prostaglandins (PGs). The enzyme exists in two isoforms COX-1 and COX-2. The inducible COX-2 isoform has been shown to be present in up to 80% of breast cancers, high expression correlating with low rates of apoptosis, increased angiogenesis and poor prognosis. Both non-steroidal anti-inflammatory drugs (NSAIDs) and selective inhibitors to COX-2 have been associated with anti-tumoural properties, decreasing the rates of tumour growth, increasing apoptosis and inhibiting angiogenesis. A variety of cellular mechanisms have been suggested, but the exact mechanisms of action remain unclear. COX-2 inhibitors have the potential to be used either alone, or in combination with other agents such as aromatase inhibitors (AIs), monoclonal antibodies (i.e. trastuzumab) or chemotherapeutic agents as novel therapeutic strategies against breast cancer. However the potential cardiac toxicity of the COX-2 selective compounds needs to be fully addressed, with the future development of either safe dosing regimes or new compounds.

Endocrine adjuvant therapy for breast cancer has been associated with a decrease in bone mineral density (BMD) and bone loss. For aromatase inhibitors, this bone loss is likely to be the most significant limitation to their long-term use. Treatments traditionally used to counteract his effect include exercise and supplementation with calcium and vitamin D. A newer treatment is the use of bisphosphonates, a class of drugs that reduce osteoclast activity. Clinical trials currently underway to examine the effect of bisphosphonate treatment on breast cancer patients have shown improvement in bone strength. Additional benefits of bisphosphonates, currently under study, give this class of drugs an important role to play in the treatment of cancer treatment-induced bone loss.

At least four cell types in mouse mammary epithelium, three in human, and three in cow are now known to be proliferation competent. Some evidence indicates that pregnancy may confer proliferative competency on a new cell type. These cells are widely seen as stem and progenitor cells that maintain the epithelium and produce lactational units during pregnancy. Evolutionarily conserved developmental signaling pathways active in germinal and neuronal stem cell proliferation and differentiation in drosophila and mammalian development are implicated in mammary tumorigenesis. In adult tissues this signaling is retained, is regulated by stem cell niches and operates to create new tissue and maintain tissue form and integrity. Disruption of this signaling may abrogate maintenance of the stem cell niche and lead to preneoplastic conditions.

Citation of original article:

K. Kerlikowske, J. Shepherd, J. Creasman, J. A. Tice, E. Ziv, S. R. Cummings. Are breast density and bone mineral density independent risk factors for breast cancer. Journal of the National Cancer Institute 2005; 97(7): 368–74.

Abstract of the original article

Background: Mammographic breast density and bone mineral density (BMD) are markers of cumulative exposure to estrogen. Previous studies have suggested that women with high mammographic breast density or high BMD are at increased risk of breast cancer. We determined whether mammographic breast density and BMD of the hip and spine are correlated and independently associated with breast cancer risk. Methods: We conducted a cross-sectional study (N = 15 254) and a nested case-control study (of 208 women with breast cancer and 436 control subjects) among women aged 28 years or older who had a screening mammography examination and hip BMD measurement within 2 years. Breast density for 3105 of the women was classified using the American College of Radiology Breast Imaging Reporting and Data System (BI-RADS) categories, and percentage mammographic breast density among the case patients and control subjects was quantified with a computer-based threshold method. Spearman rank partial correlation coefficient and Pearson's correlation coefficient were used to examine correlations between BI-RADS breast density and BMD and between percentage mammographic breast density and BMD, respectively, in women without breast cancer. Logistic regression was used to examine the association of breast cancer with percentage mammographic breast density and BMD. All statistical tests were two-sided. Results: Neither BI-RADS breast density nor percentage breast density was correlated with hip or spine BMD (correlation coefficient = −.02 and −.01 for BI-RADS, respectively, and −2.06 and .01 for percentage breast density, respectively). Neither hip BMD nor spine BMD had a statistically significant relationship with breast cancer risk. Women with breast density in the highest sextile had an approximately threefold increased risk of breast cancer compared with women in the lowest sextile (odds ratio: 2.7; 95% confidence interval: 1.4–5.4); adjusting for hip or spine BMD did not change the association between breast density and breast cancer risk. Conclusion: Breast density is strongly associated with increased risk of breast cancer, even after taking into account reproductive and hormonal risk factors, whereas BMD, although a possible marker of lifetime exposure to estrogen, is not. Thus, a component of breast density that is independent of estrogen-mediated effects may contribute to breast cancer risk.

Citation of original article:

A. Boire, L. Covic, A. Agarwal, S. Jacques, S. Sherifi, A. Kuliopulos. PAR1 is a matrix metalloprotease-1 receptor that promotes invasion and tumorigenesis of breast cancer cells. Cell 2005; 120(3): 303–13.

Abstract of the original article

Protease-activated receptors (PARs) are a unique class of G protein-coupled receptors that play critical roles in thrombosis, inflammation, and vascular biology. PAR1 is proposed to be involved in the invasive and metastatic processes of various cancers. However, the protease responsible for activating the proinvasive functions of PAR1 remains to be identified. Here, we show that expression of PAR1 is both required and sufficient to promote growth and invasion of breast carcinoma cells in a xenograft model. Further, we show that the matrix metalloprotease, MMP-1, functions as a protease agonist of PAR1 cleaving the receptor at the proper site to generate PAR1-dependent Ca2+ signals and migration. MMP-1 activity is derived from fibroblasts and is absent from the breast cancer cells. These results demonstrate that MMP-1 in the stromal-tumor microenvironment can alter the behavior of cancer cells through PAR1 to promote cell migration and invasion.