What is breast cancer? Breast cancer is a group of diseases in which cells in breast tissue change and divide uncontrolled, typically resulting in a lump or mass. Most breast cancers begin in the lobules (milk glands) or in the ducts that connect the lobules to the nipple. What are the signs and symptoms of breast cancer? Breast cancer typically has no symptoms when the tumor is small and most easily treated, which is why screening is important for early detection. The most common physical sign is a painless lump. Sometimes breast cancer spreads to underarm lymph nodes and causes a lump or swelling, even before the original breast tumor is large enough to be felt. Less common signs and symptoms include breast pain or heaviness; persistent changes, such as swelling, thickening, or redness of the skin; and nipple changes, such as spontaneous discharge (especially if bloody), scaliness, or retraction. Any persistent change in the breast should be evaluated by a physician. How is breast cancer diagnosed? Breast cancer is typically detected either during screening, before symptoms have developed, or after a woman notices a lump. Most masses seen on a mammogram and most breast lumps turn out to be benign (not cancerous). When cancer is suspected, tissue for microscopic analysis is usually obtained from a needle biopsy (fine-needle or larger core-needle) and less often from a surgical biopsy. Selection of the type of biopsy is based on multiple factors, including the size and location of the mass, as well as patient factors and preferences and resources. How is breast cancer staged? The extent of the cancer and its spread at the time of diagnosis determines its stage, which is essential for guiding treatment options and prognosis (prediction of disease outcome). The two main staging systems for cancer are the American Joint Committee on Cancer (AJCC) staging system, typically used in clinical settings, and the Surveillance, Epidemiology, and End Results (SEER) summary staging system, used for descriptive and statistical analysis of tumor registry data. The AJCC system was recently updated (effective January 2018) to add prognostic stage groups.1 AJCC anatomic stage is based on extent of the cancer (in the breast, regional lymph nodes, and distant spread), while prognostic stage also includes information on the presence of estrogen receptors (ER), progesterone receptors (PR), levels of human epidermal growth factor receptor 2 (HER2, a growth-promoting protein) and/or extra copies of the HER2 gene (HER2+/HER2-), and grade (reflecting how closely the cancer’s microscopic appearance looks like normal breast tissue). In this document, we generally refer to the SEER summary stage except in the section on the description of breast cancer treatment (page 23), which references AJCC anatomic stage. According to the SEER summary stage system: • In situ stage refers to the presence of abnormal cells that are confined to the layer of cells where they originated. • Local stage refers to invasive cancer that is confined to the breast. • Regional stage refers to cancer that has spread to surrounding tissue and/or nearby lymph nodes. • Distant stage refers to cancer that has spread to distant organs and/or lymph nodes, including nodes above the collarbone. 2 Breast Cancer Facts & Figures 2019-2020 What are the types of breast cancer? In Situ Historically, ductal carcinoma in situ (DCIS) and lobular carcinoma in situ (LCIS), also known as lobular neoplasia, were considered the two main types of in situ breast cancer. However, LCIS is generally believed to be a benign condition associated with increased breast cancer risk, but without the potential to progress to invasive cancer, so it was removed from the latest edition of the AJCC breast cancer staging system.2 DCIS, on the other hand, is a precursor to invasive cancer, although not all DCIS progresses. In fact, DCIS sometimes grows so slowly that even without treatment it would not affect a woman’s health. Long-term studies have found that only 20%-53% of women with untreated DCIS are ultimately diagnosed with invasive breast cancer.3-5 DCIS patients who are premenopausal at diagnosis or who had their DCIS detected by palpation are at greater risk of being diagnosed with a future invasive breast cancer.6, 7 During 2012-2016, DCIS represented 16% of all breast cancer diagnoses.8 See page 13 for additional information on DCIS and LCIS. More information can also be found in the Cancer Facts & Figures 2015, Special Section: Breast Carcinoma In Situ. Invasive Most (81%) breast cancers are invasive, or infiltrating, which means the abnormal cells have broken through the walls of the glands or ducts where they originated and grown into surrounding breast tissue. Although breast cancer was historically referred to as a single disease, it is now considered a group of diseases, consisting of four major molecular subtypes and at least 21 distinct histological subtypes (type of tissue in which the cancer originates) that differ in risk factors, presentation, response to treatment, and outcomes. Histologic subtypes Histology is based on the size, shape,