Breast cancer refers to the erratic growth and proliferation of cells that occur in breast tissue. Although breast cancer is a malignancy that originates from the parenchyma of the breast, not every breast cell has the same cell of origin. Breast cancer can originate from either the cells that line the ducts, or from cells within the breast lobules. Malignant cancers develop initially on the epithelial level, indicated by an increasing number of proliferating epithelial cells. If detected at this point of development, the cancer can be reversible. If it progresses further and develops into carcinoma in situ, the cancer becomes irreversible. The disease can then break out of the duct to invade the rest of the breast tissue and will spread after gaining access to the lymphatic and blood vessel pathways.
Breast cancer is the most frequently occurring malignancy in women, and its mortality rate is high compared to other cancers. The National Cancer Institute estimated that 207,090 women were diagnosed with breast cancer and 39,840 women died of the disease in 2010 in the United States. In 2008, Coleman et al. reported varying breast cancer survival rates worldwide, ranging from 80% or above in high-income countries such as North America, Sweden, and Japan, to around 60% in middle-income countries, and below 40% in low-income countries. The decreased survival rate in low-income countries can be attributed to the unavailability of affordable screening modalities (such as mammography), resulting in cancer being detected at later stages, and therefore causing a decrease in the survival rate. Even though breast self-examination (BSE) and clinical breast examination (CBE) are affordable options to women in low-income countries, a lack of education regarding these methods and/or the incapability of these methods to detect breast cancer at its earliest stages can also add to the decreased survival probability.