There are many different types of breast cancer defined by how much they have grown or spread, and how they behave. One way to categorize different types of breast cancer is through an invasive/non-invasive dichotomy. When breast cancer is called invasive, it means it has spread into the surrounding breast tissue:
- Invasive ductal carcinoma (IDC), starts in the milk ducts, the tubes that carry milk from the lobules to the nipple. It is the most common type of breast cancer as about 80% of all breast cancers are invasive ductal carcinomas.
- Invasive lobular carcinoma (ILC), starts in the lobules, the glands in the breast that produce milk. It is the second most common type of breast cancer with about 10% of all invasive breast cancers being invasive lobular carcinomas.
- Triple-negative breast cancer is an aggressive type of invasive breast cancer that tests negative for estrogen receptors and progesterone receptors and doesn’t have extra HER2 proteins. About 12% of all invasive breast cancers are triple-negative.
- Metastatic breast cancer is a breast cancer that has spread to parts of the body away from the breast, such as the bones, liver, lungs, or brain. Breast cancer can come back in another part of the body months or years after the original treatment, but some people are initially diagnosed with metastatic disease.
When breast cancer is called non-invasive it means it has not spread beyond the breast tissue where it started. The two main types are:
- Ductal carcinoma in situ (DCIS), is a breast cancer that has not spread outside the milk ducts where it started. DCIS isn’t life threatening, but is considered a precursor to invasive breast cancer and increases the risk of developing an invasive breast cancer later in life. About 16% of all breast cancer diagnoses are DCIS.
- Lobular carcinoma in situ (LCIS), is a breast cancer that has not spread outside the lobules where it started. Despite its name, LCIS is a benign breast condition and is not a true breast cancer.
In addition to the types mentioned above, there are dozens of other (less common) types and subtypes of breast cancer, such as adenoid cystic carcinoma, low-grade adenosquamous carcinoma, and medullary carcinoma.
Determining the type is imperative in deciding what kind of treatment is best for each patient. Genomic research has also led to a more specific classification of breast cancers based on their genes and proteins. 60% of breast cancers are estrogen-positive, for example, while 20% are HER2-positive, and another 20% triple-negative.
Sources:
BreastCancer.org
CancerCenter.com