**3. Luminal subtypes**

104 Breast Cancer – Focusing Tumor Microenvironment, Stem Cells and Metastasis

that oral contraceptives cause any increase in breast cancer risk. Long term use of postmenopausal hormone therapy is associated with higher risk of breast cancer. In contrast, short-term HT appears not to increase the risk significantly, although it may make mammographic detection more difficult. Environmental toxic agents such as Organochlorines include polychlorinated biphenyls (PCB's), dioxins, and organochlorine pesticides such as DDT are weak estrogens with high lipophilic properties and as a result, can store in adipose tissues. Some studies suggest that exposure to these chemicals will increase the risk of bearing breast cancer, however the data are controversial and more

Age and gender are among the strongest risk factors for breast cancer. Breast cancer occurs 100 times more frequently in women than in men. Incidence rates increase with age until

Ethnic difference is another factor affecting breast cancer prevalence. For example, in United States, breast cancer is more common among whites. Much of these differences arise from lifestyle factors and social conditions. Furthermore, there are marked variations in breast cancer incidence and mortality among countries Women with higher educational, occupational and economic level are at greater risk because of their reproductive pattern including age of parity and age of first birth. Ethnic differences in estrogen and progesterone receptor subtypes have been also determined as important factors that affect the probability of breast cancer (7). In a Multiethnic Cohort Study, various status of estrogen receptor (ER)/progesterone receptor (PR) including ER-/PR-, ER+/PR+, ER-/PR+ and ER+/PR- have been reported and ER/PR status varied significantly across racial/ethnic groups even within the same tumor stage. Compared to whites, the high prevalence of hormone receptor-negative tumors in African-American women may contribute to their

Nowadays, beside conventional use of grade, histology, and immunohistochemical analysis, changes in gene expression during bearing tumors are used as an instrument to classify breast cancer. Molecular profiling make us capable for better understanding of breast cancer, more precision in determining subtypes and better prediction of clinical outcome and response to therapy. New instruments like microarray kits provide the possibility for simultaneous studying of the expression of thousands of genes in a breast cancer cells and finding out the Gene expression profile. Future applications will take the same approach to proteins (proteomics), genome-wide germline variability (single nucleotide polymorphisms), or cellular metabolism (metabolomics). Based on these methods, several distinct breast cancer subtypes have been identified including two main subtypes of estrogen receptor (ER)-negative tumors and basal-like and human epidermal growth factor receptor-2 (HER2)-enriched, and two subtypes of ER-positive tumors including luminal A and luminal B. These subtypes differ markedly in prognosis and in the therapeutic targets

The luminal cancers, luminal A and luminal B, so called because they are characterized by expression of genes also expressed by normal breast luminal epithelial cells, have overlap with ER-positive breast cancers. There are also several subtypes characterized by low expression of hormone receptor-related genes (ER-negative), one of which is called the "HER2-enriched" subtype (previously called HER2+/ER-) and another called the "basal-like"

researches should be done.

about the age of 45 to 50.

high breast cancer mortality (8).

they express.

**2. Breast cancer classification** 

The name "luminal" derives from similarity in expression between these tumors and the luminal epithelium of the breast; they typically express luminal cytokeratins 8 and 18. These are the most common subtypes, make up the majority of ER-positive breast cancer, and are characterized by expression of ER, PR, and other genes associated with ER activation.
