Breast cancer Cancer occurs when changes called mutations take place in genes that regulate cell growth. The mutations let the cells divide and multiply in an uncontrolled way. Breast cancer is cancer that develops in breast cells. Typically, the cancer forms in either the lobules or the ducts of the breast. Lobules are the glands that produce milk, and ducts are the pathways that bring the milk from the glands to the nipple. Cancer can also occur in the fatty tissue or the fibrous connective tissue within your breast. The uncontrolled cancer cells often invade other healthy breast tissue and can travel to the lymph nodes under the arms. The lymph nodes are a primary pathway that help the cancer cells move to other parts of the body. See pictures and learn more about the structure of the breast.Breast cancer symptomsIn its early stages, breast cancer may not cause any symptoms. In many cases, a tumour may be too small to be felt, but an abnormality can still be seen on a mammogram. If a tumour can be felt, the first sign is usually a new lump in the breast that was not there before. However, not all lumps are cancer. Each type of breast cancer can cause a variety of symptoms. Many of these symptoms are similar, but some can be different. Symptoms for the most common breast cancers include:a breast lump or tissue thickening that feels different than surrounding tissue and has developed recentlybreast painred, pitted skin over your entire breastswelling in all or part of your breasta nipple discharge other than breast milkbloody discharge from your nipplepeeling, scaling, or flaking of skin on your nipple or breasta sudden, unexplained change in the shape or size of your breastinverted nipplechanges to the appearance of the skin on your breastsa lump or swelling under your armIf you have any of these symptoms, it doesn’t necessarily mean you have breast cancer. For instance, pain in your breast or a breast lump can be caused by a benign cyst. Still, if you find a lump in your breast or have other symptoms, you should see your doctor for further examination and testing. Learn more about possible symptoms of breast cancer.Types of breast cancerThere are several types of breast cancer, and they are broken into two main categories: “invasive” and “non-invasive,” or in situ. While invasive cancer has spread from the breast ducts or glands to other parts of the breast, non-invasive cancer has not spread from the original tissue.These two categories are used to describe the most common types of breast cancer, which include:Ductal carcinoma in situ. Ductal carcinoma in situ (DCIS) is a non-invasive condition. With DCIS, the cancer cells are confined to the ducts in your breast and haven’t invaded the surrounding breast tissue. Lobular carcinoma in situ. Lobular carcinoma in situ (LCIS) is cancer that grows in the milk-producing glands of your breast. Like DCIS, the cancer cells haven’t invaded the surrounding tissue.