The breasts are hormonally regulated organs made up of a range of tissue types: lobules, which make and secrete milk; ducts, which carry the milk from the lobules to the nipple; fat and connective tissue, which support the shape of the breast; lymph nodes and blood vessels; and the nipple, which secretes milk during lactation. The breasts undergo growth cycles during puberty and throughout life during pregnancy. Cancer can result from deregulation of the growth cycle in any of the cell types of the breast, leading to a range of forms of breast cancer.
Breast cancer can originate from the lobules of the breast. The tumor within the lobule can be considered benign, called lobular carcinoma in situ (LCIS), or it can be aggressive and metastatic, called infiltrating lobular carcinoma. LCIS is not technically a cancer, since it does not spread beyond the lobules, but it can develop into cancer and puts the patient at greater risk of developing invasive cancer in the future. According to Stanford Medicine, infiltrating lobular carcinoma accounts for about 10 percent of breast cancer cases, making it the second most common form of breast cancer.
Stanford reports that lobular carcinomas may not show up on a mammogram, and are usually diagnosed by a biopsy. Treatment for lobular carcinomas may involve surgery, chemotherapy or radiation therapy.
The ducts, which are tubes that connect the lobules to the nipple to facilitate lactation, are the most common site for breast cancer. The type of ductal breast cancer depends on the aggressiveness of the tumor: non-invasive ductal tumors are called ductal carcinoma in situ, or DCIS, while metastatic ductal tumors are called infiltrating ductal carcinomas. Stanford Medicine reports that infiltrating ductal carcinomas are the most common type of breast cancer, accounting for around 75 percent of breast cancer diagnoses.
Ductal carcinomas are generally visible on mammograms, with the diagnosis being confirmed by analyzing a biopsy sample. Once diagnosed, ductal tumors can be treated with surgery, radiation therapy and chemotherapy.
The ducts and tubules are the most common sites of breast cancer development, but cancer can also occur in the nipples. Cancer of the nipple is referred to as Paget's disease. Stanford Medicine reports that Paget's disease accounts for about 4 percent of breast cancer cases.
According to the University of California, San Diego, scientists are not sure what causes Paget disease: whether cells within the nipple may become cancerous and lead to the disease, or cancerous cells migrate from another tumor to the nipple and cause the disease. The symptoms of Paget disease are itching, scaly red skin on the nipple, as well as irregular or bloody nipple discharge. Paget disease is usually found in combination with other forms of breast cancer.