The chances that a particular breast lump could be cancerous depends on many factors, including a woman's past medical history, physical examination, and mammogram and ultrasound results.

History

Age is the biggest risk factor for breast cancer. In other words, most cases of breast cancer occur due to the fact that the risk of breast cancer increases with age. Most women with breast cancer do not have a history of breast cancer. A woman who has had a prior breast cancer or who has a family history of breast cancer is certainly at risk herself, especially if multiple family members are involved, the cases occurred at a young age, or if the cancer involved both breasts of a single family member.

Women who have received radiation therapy to the chest area as treatment for another cancer have a significantly increased risk for breast cancer.

Genetic factors

About 5% to 10% of breast cancer cases have been shown to be related to inherited gene changes (mutations). The most common mutations are those of the BRCA1 and BRCA2 genes, although other genetic mutations may also lead to breast cancers.

Abnormal findings on previous breast biopsies

The finding of certain conditions on previous breast biopsies can also increase the risk for developing breast cancer. Pre-cancerous growths and growths noted on a breast biopsy that represent an increased risk for the development of breast cancer include the following:

• Ductal carcinoma-in-situ (DCIS) is an uncontrolled growth of cells that has not spread beyond the milk duct where it is located. DCIS consists of cancer cells that have not invaded other tissues. Therefore, DCIS is an early stage of breast cancer and is the most common type of noninvasive breast cancer. DCIS is not life-threatening, but must be treated. Women with DCIS have an increased risk for developing a recurrence of the cancer or for development of a new cancer in either breast.
• Lobular carcinoma-in-situ (LCIS) is considered to be a condition in which abnormal cells are confined to the lobules in the breast (the glands that produce milk). Unlike DCIS, LCIS is not considered to have a high probability of becoming a cancer, but it is a sign of risk for that breast or the opposite breast for developing a cancer. Therefore, women with LCIS have a greater chance of developing breast cancer in either breast.
• Proliferative disease of the breast is a benign condition, but it can be a signal that breast cancer may develop in the future. Ductal hyperplasia (the excessive growth of normal cells within the breast ducts) and atypical hyperplasia (overgrowth of abnormal cells in the ducts or lobules that is not serious or extensive enough to qualify as DCIS or LCIS) are examples of conditions that increase the overall risk for developing breast cancer. Not surprisingly, women with atypical hyperplasia have a higher risk than do those with usual ductal hyperplasia (without atypia, or abnormal cells).

Women with DCIS, LCIS, atypical hyperplasia, or proliferative disease are at even higher risk of developing breast cancer if they have a history of breast cancer in the family.

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