Breast cancer is not one single disease but a group of related cancers that affect different parts of the breast and behave in different ways. Some types grow slowly and remain contained in the breast, while others spread more quickly to nearby tissue or other parts of the body. Breast cancer type is determined by which receptors the cancerous cells carry and how they respond to hormones or other growth signals. These differences affect how the cancer is diagnosed, treated, and monitored.
The most common types of breast cancer are invasive ductal carcinoma (IDC) and invasive lobular carcinoma (ILC). Other types of breast cancer include ductal carcinoma in situ (DCIS), triple-negative breast cancer (TNBC), inflammatory breast cancer (IBC), and metastatic breast cancer (MBC), among other less common types.
There are different types of breast cancer because the breast is made up of several kinds of cells, and cancer can begin in any of them. Some cancers start in the ducts that carry milk, others in the glands that produce milk, and some in the surrounding breast tissue. Breast cancer types are classified based on several key factors, including where the cancer starts in the breast, whether it has spread to surrounding tissue, and the specific characteristics of the cancer cells themselves.
Because every cancer develops from a unique combination of cells and mutations, breast cancer varies from person to person, leading to different types of breast cancer that each require a specific treatment approach.
The type of breast cancer someone has directly impacts treatment options and expected outcomes. Some types of breast cancer may respond well to hormone-based treatments, while others may require chemotherapy, targeted therapy, or a combination of approaches. Because certain cancers are more sensitive to specific drugs, doctors can tailor treatment to be more effective and less harmful.
The type of breast cancer someone has also influences prognosis. Slower-growing cancers often have good long-term outcomes, while more aggressive forms may need intensive treatment and closer monitoring. By understanding the cancer’s characteristics, patients and healthcare providers can create a personalized treatment plan that improves the chances of successful recovery and long-term survival.
Ductal carcinoma in situ (DCIS) is considered the earliest form of breast cancer and accounts for approximately 20-25% of all new breast cancer cases in the United States. DCIS begins in the milk ducts, where the cancerous cells are contained within the ducts and have not spread into the surrounding breast tissue or nearby lymph nodes. Because cancerous cells have not spread from their original location, DCIS is considered “non-invasive.” While not invasive, DCIS requires prompt treatment to prevent progression into invasive cancer. Early detection of DCIS through mammograms increases the likelihood of successful treatment and outcomes.
Invasive ductal carcinoma (IDC) is the most common type of invasive breast cancer, accounting for about 80% of diagnoses. In IDC, cancer cells begin in the breast’s milk ducts and then spread into the surrounding healthy breast tissue. This ability to grow beyond their original location is what makes the cancer “invasive.” If left undetected or untreated, IDC can spread beyond the breast tissue into other areas of the body, starting by invading the lymph nodes or bloodstream. When IDC is diagnosed, it is assigned a stage between 1 and 4.
Invasive lobular carcinoma (ILC) is the second most common form of invasive breast cancer, accounting for approximately 10-15% of diagnoses. It is a slow-growing cancer that begins in the milk glands (lobules) of the breast and has invaded, or spread, into the surrounding breast tissue or other areas of the body. Because ILC can be difficult to detect through early screening, it can grow large and spread before it is diagnosed. Advanced screening measures, such as breast MRI, can help detect ILC.
Triple-negative breast cancer (TNBC) is an aggressive form of invasive breast cancer and accounts for approximately 10-15% of all breast cancer cases. TNBC lacks the three receptors—estrogen, progesterone, and HER2—that are usually found in breast cancer, making common hormonal therapies ineffective. Therefore, surgery, radiation, and chemotherapy are commonly used to treat TNBC.
Inflammatory breast cancer (IBC) is a rare but aggressive form of invasive breast cancer, accounting for only 1-5% of all breast cancer cases. IBC is Stage 3 breast cancer and occurs when cancer cells spread to the skin and lymph vessels of the breast, often causing the breast to appear red, swollen, and warm. It also often causes a rash on the breast. IBC tends to grow and spread quickly, so early recognition and immediate treatment are critical.
Metastatic breast cancer (MBC) means that the cancer has spread beyond the breast into other parts of the body, such as the bones, liver, lungs, or brain. MBC is Stage 4 breast cancer and will be a part of the patient’s life for the rest of their life. While MBC is not curable, it is treatable. Many people diagnosed with MBC live fulfilling lives for years with ongoing treatment and support.
Lobular carcinoma in situ (LCIS) is not breast cancer. It is a condition where non-cancerous, atypical (abnormal) cells are found in the lobules (glands that produce breast milk) of the breast. In LCIS, the atypical cells have not spread outside of the lobules into the surrounding breast tissue. It typically does not cause any symptoms or form a lump and is often found during a biopsy for another issue. LCIS is considered a risk factor for developing cancer and should be closely followed with regular monitoring and personalized risk-reduction strategies.
In addition to the more common forms of breast cancer, there are several rare types that require specialized care. These include triple-positive breast cancer, medullary carcinoma, tubular carcinoma, mucinous carcinoma, Paget’s disease of the breast, metaplastic breast cancer, phyllodes tumors, and angiosarcoma of the breast. Though uncommon, these types of breast cancer can vary widely in appearance, behavior, and treatment approach, making accurate diagnosis and personalized care essential.
Male breast cancer is rare and accounts for less than 1% of all breast cancer diagnoses in the United States. Though less common, male breast cancer is often diagnosed at a later stage, making it more difficult to treat. Awareness of male breast cancer symptoms like lumps, nipple discharge, or changes in breast tissue is key to the early detection and treatment of male breast cancer.
Although pregnancy does not cause breast cancer or affect the type of breast cancer someone has, it is possible to be diagnosed during pregnancy or shortly after. This is known as pregnancy-associated breast cancer (PABC). Because of hormonal changes and natural breast changes during pregnancy, diagnosis can be more challenging or delayed. Treatments may need to be adjusted to protect both the mother and the developing baby, depending on the type of cancer, stage, and period of gestation.
