Breast cancer occurs when normal cells within the breast transform into tumors that grow uncontrollably. The causes of breast cancer are complex and can result in the formation of a variety of different types of tumors. Contact your doctor if you experience any lumps, pain or inflammation in the breast region. It may be a warning sign of a developing tumor in the breast.
In Situ Breast Tumors
According to the American Cancer Society, in situ tumors are tiny collections of abnormal cells in the breast that represent the earliest stages of breast cancer. These tumors are not usually detectable by touch but can be seen on a mammogram. In situ tumors are sub-typed based on their cellular origins. The majority of in situ tumors develop from cells lining the milk ducts of the breast, referred to as ductal carcinoma in situ. Another subtype of in situ tumor can develop from the milk-producing lobules of the breast, called lobular carcinoma in situ. In situ tumors are sometimes referred to as Stage 0 breast cancer.
Invasive Breast Tumors
As in situ tumors grow, they invade other tissues of the breast, forming a palpable, solid mass. According to the American Cancer Society, at this stage, tumors are known as invasive tumors and also referred to based on their cellular origin as invasive ductal carcinoma or invasive lobular carcinoma. These tumors can be graded as Stage I, II or III depending on the size of the tumor and whether or not it has formed contacts with the lymphatic and vascular systems.
HER2-Positive Tumors
Breast cancer results from a number of different genetic changes that occur in the level of DNA within a breast cell. The American Cancer Society describes one such change as a multiplication of the HER2 gene. HER2 can signal the growth of breast tumor cells. Breast tumors that are found to have multiplications of the HER2 gene are called HER2-positive tumors, while those lacking this genetic change are known as HER2-negative. HER2 status is important because it will determine which chemotherapy options will best serve the patient.
Triple-Negative Breast Tumors
Changes in breast cells may also cause these cells to lose receptors for the hormones estrogen and progesterone. Breastcancer.org explains that tumors lacking estrogen receptor (ER) are known as ER-negative tumors, while those without progesterone receptor (PR) are called PR-negative. Tumors lacking HER2, ER and PR are referred to as triple-negative tumors. As many chemotherapeutic drugs for breast cancer target receptors for estrogen, progesterone or HER2, triple-negative tumors can require unique treatment regimens.
