Breast cancer is the cancer, which originates from the breast tissue. The etiology of this disease is still under investigation and more causes need to fixed on priority basis. Given below is a brief description of some of the causes that underlie the pathogenesis of this disease collectively:
i) The incidence of breast cancer is partly dependent on age, as the age of women progresses, the chances of getting the disease are likely to increase.
ii) Risk factor also increases among women with a positive family history of breast cancer.
iii) Two other factors related with the disease are early start of menses and early menopause.
iv) Exposure to harmful chemicals at the workplace like organochlorines.
v) Hormone replacement therapy
vi) Radioactive rays are known to be carcinogenic, therefore exposure of the same increases the chances of breast cancer.

Breast cancer is the most frequently diagnosed threatening cancer among women, accounting for nearly one-third of all cancers diagnosed in women in the United States. In the year 2010, about more than 2,00,000 United States women were diagnosed with breast cancer and more than 40,000 died of this disease. Although men can also develop breast cancer, it is 100-fold less frequent in men than in women.

Early detection is critically important in reducing breast cancer mortality, and screening for breast cancer by self-examination and mammography is recommended by the American Cancer Society and the National Cancer Institute. It is estimated that annual screening by mammography for women over age 40 reduces breast cancer mortality by about 30%. The benefits of early detection are clearly apparent in survival rates for women diagnosed with breast cancer. The cure rate for localized breast cancer is approximately 90%, but this drops to about 70% for cancers that have spread to regional lymph nodes and to less than 20% for cancers that have metastasized to distant body sites.

Molecular and Cellular Basis
Breast cancers develop as a result of mutations in a variety of oncogenes and tumor suppressor genes. Approximately 5-10% of breast cancers are inherited as a result of mutations in the BRCA1 and BRCA2 tumor suppressor genes. Mutations in BRCA1 and BRCA2 are not generally found in non-inherited breast cancers, which may instead involve mutations in several other oncogenes and tumor suppressor genes, including erbB-2, c-myc, D1, p53, and Rb.

The erbB-2 gene, which encodes a receptor protein-tyrosine kinase, is amplified and expressed at high levels in about 30% of breast cancers. Elevated expression of erbB-2 is characteristic of rapidly progressing metastatic cancers with a poor prognosis. Perhaps ironically, then, the ErbB-2 protein has served as the first oncogene target against which anew anticancer drug has been approved for clinical use by the FDA.

Recent Targeted Drug Approved for Treatment
Like other cancers, breast cancer is generally treated by surgery, radiation and chemotherapy with cytotoxic drugs that damage DNA or act as general inhibitors of cell division. In addition, some breast cancers respond to hormone therapy, which block the growth-promoting effects of estrogens on the cancer cells. Herceptin, a monoclonal antibody against the ErbB-2 oncogene protein, has now been added to the arsenal of drugs used to treat breast cancer, specifically for those women whose cancers overexpress ErBb-2. Based on the results on crucial experiments, the FDA approved Herceptin for the treatment of metastatic breast cancer in 1998. It is used specifically for those patients whose tumors express elevated levels of the ErbB-2 oncogene protein, and may be used either alone or in combination with other anticancer drugs.

In conclusion, the incidence of breast cancer increases with age, and more than 75% of breast cancers are diagnosed in women over 50. Other factors that increase the risk of breast cancer include a family history of the disease and exposure to hormones that stimulate the proliferation of breast epithelial cells. Early menarche (before age 12), late menopause (after age 55), and a late age for first childbirth (after 30) are all associated with an increased risk of breast cancer as the result of effects on reproductive hormones. The risk of breast cancer is also increased by recent use of oral contraceptives and long-term postmenopausal estrogen replacement therapy.

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