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Causes
By Mayo Clinic staff
It's not clear what causes atypical hyperplasia. Atypical hyperplasia forms when breast cells become abnormal in number, size, shape, appearance and growth pattern. Location of the abnormal cells within the breast tissue — the lobules or the milk ducts — determines whether the cells are atypical lobular hyperplasia or atypical ductal hyperplasia.
Atypical hyperplasia is thought to be part of the complex, multistep process by which breast cancer develops. The process begins when normal cell development and growth become disrupted, causing an overproduction of normal-looking cells (hyperplasia). Atypical hyperplasia occurs when the excess cells stack upon one another and begin to take on an abnormal appearance. The abnormal cells can continue to change in appearance and multiply, evolving into noninvasive (in situ) cancer, in which cancer cells remain confined to the area where they start growing. Left untreated, the cancer cells may eventually become invasive cancer, invading surrounding tissue, blood vessels or lymph channels.
- Non-cancerous breast conditions. American Cancer Society. http://www.cancer.org/docroot/CRI/content/CRI_2_6X_Non_Cancerous_Breast_Conditions_59.asp. Accessed Aug. 19, 2009.
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- Degnim AC, et al. Stratification of breast cancer risk in women with atypia: A Mayo cohort study. Journal of Clinical Oncology. 2007;25:2671.
- Dupont WD, et al. Breast cancer risk associated with proliferative breast disease and atypical hyperplasia. Cancer. 1993;71:1258.
- Kiluk JV, et al. High-risk benign breast lesions: Current strategies in management. Cancer Control. 2007;14:321.
- Breast cancer screening and diagnosis. Fort Washington, Pa.: National Comprehensive Cancer Network. http://www.nccn.org/professionals/physician_gls/PDF/breast-screening.pdf. Accessed Aug. 21, 2009.
- Breast cancer risk reduction. Fort Washington, Pa.: National Comprehensive Cancer Network. http://www.nccn.org/professionals/physician_gls/PDF/breast_risk.pdf. Accessed Aug. 21, 2009.
