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Home What is Breast Cancer Diagnosis Development of Breast Cancer

Development of Breast Cancer

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After receiving the diagnosis of breast cancer, you may find yourself wondering, “How did I get breast cancer?”  There are many risk factors (as described on the Risk Factors page) that increase the likelihood of developing breast cancer, however there are also many people who have an apparent low risk that still end up developing breast cancer.  So how does breast cancer develop?

The development of breast cancer is very complex and many details are still being researched.  Cancer is the result of uncontrollable cell growth.  These cells may invade surrounding tissues and spread to other areas of the body.  This distant invasion is known as metastasis.  As with all types of cancer, breast cancer begins with acquired and/or inherited mutations.  Some examples of inherited mutations include BRCA1 and BRCA2.  Mutations occur in the DNA of a specific cell from the tissue type that the cancer originates, in this case breast tissue.  In normal cells, cell mutations are either detected and repaired by the cell itself or the body’s immune system eliminates the cell to prevent further damage.  When this system fails, mutations are able to escape these protective measures, and  this can result in the production and replication of damaged cells that are predisposed to become cancerous.  When there are enough mutations in important genes, the cell can no longer be regulated by itself or be recognized as altered by the immune system, leading to uncontrolled growth and ultimately cancer.


Mutations can occur for a variety of reasons.  These include being born with a particular mutation, exposure to radiation or certain chemicals, certain infections, and persistent inflammation.  Mutations can also occur spontaneously.  As mentioned before, mutations occur in DNA. DNA contains four bases that make up the cell’s genetic makeup.  These four bases are adenine (A), cytosine (C), guanine (G), and thymine (T).   A large group of DNA bases in a series associated with a specific function is known as a gene.  If these bases are modified, replaced by another base, or if one or more bases is deleted or inserted, mutations can occur.  Mutations in DNA thereby change the associated gene.  It is these alterations in crucial genes that either encode or regulate crucial proteins that may lead to uncontrolled growth and therefore cancer.  Mutations that are important in the specific development of breast cancer include BRCA1, BRCA2, and HER-2, which also determines a specific type of breast cancer that is further described on the “What is Her 2 Neu?” page.


In addition to the many risk factors that may predispose one to breast cancer, there are also breast diseases that carry an increased risk of developing breast cancer.  These include typical hyperplasia, sclerosing adenosis, papilloma, complex radial scar, and fibroadenoma which all carry a 1.5-2 fold increased risk.  Atypical hyperplasia has a 4-5 fold increased risk, and carcinoma in situ has an 8-10 fold increased risk in developing breast cancer.

In summary, one cause cannot be attributed to the development of all breast cancers. Rather, it is due to the summation of a large number of both genetic and environmental factors.

Craig Boddy BS, Shikha Jain MD


Kumar V, Abbas AK, Faustro N, Aster J. Robbins and Cotran Pathologic Basis of Disease. 8th ed. Philadelphia: Elsevier Saunders, 2010. p 1074.