Epidemiological risk factors for a disease can provide important clues as to the etiology, or cause, of a disease. The first case-controlled study on breast cancer epidemiology was done by Janet Lane-Claypon, who published a comparative study in 1926 of 500 breast cancer cases and 500 control patients of the same background and lifestyle for the British Ministry of Health.[13][verification needed][14]
Today, breast cancer, like other forms of cancer, is considered to be the final outcome of multiple environmental and hereditary factors. Some of these factors include:
- Lesions to DNA such as genetic mutations. Mutations that can lead to breast cancer have been experimentally linked to estrogen exposure.[15] Beyond the contribution of estrogen, research has implicated viral transformation and the contribution of ionizing radiation in causing genetic mutations.[citation needed]
- Failure of immune surveillance, a theory in which the immune system removes malignant cells throughout one's life.[16]
- Abnormal growth factor signaling in the interaction between stromal cells and epithelial cells can facilitate malignant cell growth. For example, tumors can induce blood vessel growth (angiogenesis) by secreting various growth factors further facilitating cancer growth.[citation needed]
- Inherited defects in DNA repair genes, such as BRCA1, BRCA2[17] and p53.[citation needed] People in less-developed countries report lower incidence rates than in developed countries.
Experts believe that 95 percent of inherited breast cancer can be traced to one of two genes, which they call Breast Cancer 1 (BRCA1) and Breast Cancer 2 (BRCA2). Hereditary breast cancers can take the form of a site-specific hereditary breast cancer- cancers affecting the breast only- or breast- ovarian and other cancer syndromes. Breast cancer can be inherited both from female and male relatives. [18]
Although many epidemiological risk factors have been identified, the cause of any individual breast cancer is often unknowable. In other words, epidemiological research informs the patterns of breast cancer incidence across certain populations, but not in a given individual. Due to breast cancer is vary in different racial and ethnic group. The primary risk factors that have been identified are sex,[19] age,[20] childbearing, hormones,[21] a high-fat diet,[22] alcohol intake,[23][24] obesity,[25] and environmental factors such as tobacco use, radiation[17] and shiftwork
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