What are the Different Types of Breast Cancer?
Most breast cancers are carcinomas, which are cancers that form in the epithelial cells that line organs and tissues in the body. The two main types of breast cancer carcinomas are lobular carcinoma, which starts in the lobules (glands in the breast that make milk), or ductal carcinoma, which starts in the milk ducts.
Invasive vs. Non-Invasive Breast Cancer
In the broadest sense, breast cancers are defined as being invasive or non-invasive.
- Non-invasive breast cancer: Non-invasive breast cancers are cancers that cannot spread to other areas of the body.
- Invasive breast cancer: Invasive Breast Cancer can spread beyond where it began, moving to other parts of the breast or other areas of the body.
Ductal carcinoma in situ (DCIS) is this most common form of non-invasive breast cancer. DCIS is an early stage of breast cancer (sometimes referred to as "stage zero breast cancer") that makes up about 1 in 5 new breast cancers. In patients with DCIS, the cells that line the milk ducts have become cancerous but have not spread through the ducts to nearby tissue in the breast.
To treat DCIS, your care team may recommend either a lumpectomy followed by radiation, or a mastectomy.
Invasive ductal carcinoma (IDC) is the most common form of breast cancer, accounting for approximately ~80% of invasive breast cancers. Invasive ductal carcinoma starts in the cells that line the milk ducts in the breast. After forming, IDC can break through the wall of the ducts and spread to nearby breast tissues. Once the cancer has entered other areas of the breast, it may be able to spread (metastasize) to other parts of the body through the lymph system and bloodstream.
There are both surgical and non-surgical treatment options for IDC, depending on the size of the cancer and the degree that it has spread beyond its original site. Your care team will work with you to determine the best treatment options for you.
Invasive lobular carcinoma (ILC) is a form of invasive breast cancer that forms in the breast glands that make milk, known as lobules. Similar to IDC, invasive lobular carcinoma has the potential to spread to other areas of the breast and beyond in the body.
Similar to IDC, treatment for ILC often involves surgery and may include additional non-surgical treatments.
Subtypes of Breast Cancer Based upon Receptors
As cancer cells grow, they produce molecules on their surface known as receptors. Cancer researchers have identified specific receptors that can interact or bind with specific proteins and hormones in the patient’s body, allowing the cancer cell to spread. Using specific drugs, these receptors can be blocked, slowing or stopping the spread of a cancer. Currently in breast cancer treatment, we know of three major receptor subtypes that can be targeted to slow or stop the spread of a cancer.
HER2-positive breast cancer accounts for about 15%-20% of all breast cancers. HER2 (Human epidermal growth factor receptor 2) is a protein involved in cell growth. Breast cancers with high levels of HER2 on the surface of the cancer cells are considered HER2-positive. When two of these proteins bond, they send a signal to the cell that promotes growth and multiplication.
Treatment includes anti-HER2 therapy that targets the HER2 protein. About half of HER2-positive cancers are also hormone receptor-positive/ER-positive. These patients receive treatments that target both receptors.
Hormone receptor-positive breast cancer is the most common subtype of breast cancer. Hormone receptors bind with one of two naturally occurring hormones, estrogen and progesterone, which fuel the growth of the cancer. Through hormone therapy, doctors can target this receptor by limiting the body’s production of estrogen and progesterone or by preventing the receptors from recognizing these hormones.
Triple-negative breast cancer refers to breast cancers that do not have one of the receptors listed above. Since there’s no receptor in these cancers that has a major impact on the disease when targeted, triple-negative breast cancer can be the most difficult subtype to treat. It also tends to be more aggressive, so the prognosis for this subtype is often worse than others.
Other breast cancer terms
Inflammatory breast cancer (IBC) is a rare and aggressive form of invasive breast cancer. In patients with IBC, the cancer blocks lymphatic vessels in the skin and breast tissue, causing a buildup of fluid (lymph) and, in some cases, pain, discoloration, and sudden swelling of the breast. Because IBC spreads quickly, the cancer has often already metastasized to other parts of the body at the time of diagnosis.
Due to its aggressive nature, prompt diagnosis and treatment of IBS is important. Treatment can take many forms including chemotherapy, hormonal therapy, immunotherapy, and often surgery.
Metastatic breast cancer is any form of breast cancer that has left its origin site in the breast and spread to other areas of the body. This occurs when the cancer has entered the lymph nodes or blood vessels, allowing the cancer to be carried to other sites in the body. Metastatic breast cancer is also referred to as Stage IV breast cancer.
Treatment for Metastatic Breast Cancer often requires a combination of chemotherapy, targeted drugs, and hormonal therapy, depending on the subtype of breast cancer. Surgery or radiation can also be used to slow the growth or reduce the size of tumors to relieve symptoms, but cannot be used to cure breast cancer.
Also known as metaplastic carcinoma, metaplastic breast cancer is a rare type of invasive breast cancer that contains a mix of two or more types of breast cancer cells, usually carcinoma and sarcoma. Metaplastic breast cancer is fast growing and more likely to metastasize than many other forms of breast cancer.
In order to treat metaplastic carcinoma, advanced techniques are needed to study the biology and genetics of the specific cancer and determine appropriate treatment options.
Several breast cancer subtypes can occur in men, causing male breast cancer. This is because men have the same fatty tissue, ducts, and breast cells that exist in women, though male breast cancer remains rare, comprising just 1% of total breast cancer diagnoses.
Treatment for male breast cancer can include chemotherapy, radiation, surgery, hormone therapy, and targeted therapy, and will depend on tumor size, spread, and breast cancer subtype.
Paget disease of the breast is a rare type of cancer involving the skin of the nipple and areola. Most people with Paget disease of the breast also have one or more tumors inside the same breast, either DCIS or a form of invasive breast cancer. Approximately 1%-4% of all cases of breast cancer also involve Paget disease of the breast.
Typically, treatment for Paget Disease of the breast requires a mastectomy or breast-conserving surgery followed by radiation.
