Breast cancer is often referred to as one disease, but there are many different types. All breast cancers start in the breast, so they share some similarities, but they have important differences. One difference is where tumor cells begin. Breast cancers can start in the milk ducts or lobules. Another difference is whether the cancer is non-invasive or stage 0, or invasive, which includes stages 1 through 4. Breast cancers can also look different when viewed under a microscope. Pathologists not only determine the type of cancer cells, but they can also determine the tumor size and grade, the characteristics of the tumor, such as hormone receptor status and HER2 status, and the status of lymph nodes. All of these factors help doctors predict prognosis and recommend the best treatment options. The most common types of breast cancer are those that begin in the milk ducts or lobules. Less common types include medullary, mucinous, papillary and tubular. Though they’re not specific types of tumors, some less common breast cancers include inflammatory breast cancer, Paget disease of the breast and metaplastic breast cancer. Most cancers that happen in the breast are breast carcinomas. However, in rare cases, other types of cancer, such as lymphomas and sarcomas, can also develop in the breast. Cancers that begin in other areas of the body can also metastasize, or spread, to the breast. For more information about types of breast cancer and staging, visit the Diagnosis section on komen.org.