There are many different types of breast cancer, and each case is usually classified according to its type during the diagnostic process. This is because the type of breast cancer will affect the appropriate treatment for each patient. The most common types of breast cancer are covered in more detail below.
Ductal Carcinoma in Situ (DCIS)
DCIS is an early form of breast cancer with the presence of cancerous cells inside the milk ducts of the spread that has not yet spread to other areas. It is also sometimes referred to as intraductal, non-invasive, or pre-invasive cancer. Without treatment, DCIS can spread to other areas and become an invasive breast cancer.
Invasive Ductal Carcinoma (IDC)
IDC is the most common type of breast cancer to be diagnosed. This type of breast cancer is also sometimes referred to as no special type (NST) or not otherwise specified (NOS).
There are various subtypes of invasive ductal carcinoma, which include:
- Tubular carcinoma of the breast: usually small growths (less than 1 cm) and composed of tube-shaped,;hence the name “tubules.”
- Medullary carcinoma of the breast: a soft, fleshy mass that resembles the medulla of the brain.
- Mucinous (or colloid) carcinoma of the breast: a tumor composed of abnormal cells that sit in pools of mucin.
- Papillary carcinoma of the breast: a tumor with small projection and a clear border.
- Cribriform carcinoma of the breast: abnormal cells invade the stroma of the breast in clusters between the ducts and lobules.
Invasive Lobular Carcinoma (ILC)
ILC is the second most common type of breast cancer to be diagnosed, following IDC. In this type, the cancer cells in the lobules of the breasts have spread to the surrounding tissue.
Inflammatory Breast Cancer
Inflammatory breast cancer is a rare type of breast cancer that involves reddening and inflammation of the skin of the affected breast.
Lobular Carcinoma in Situ (LCIS)
LCIS involves the abnormal growth of cells that begin in the lobules of the breasts, which are the glands at the end of the ducts that are responsible for the production of milk. In situ means that the abnormal cell growth is confined to the lobule and has not spread to surrounding tissues, although this could occur in the future.
Paget's Disease of the Nipple
Paget’s Disease of the nipple is an uncommon type of breast cancer that presents with a red and scaly rash on the skin of the breast and nipple. This type of cancer accounts for less than 5% of cases of breast cancer in the United States.
Phyllodes Tumors of the Breast
Phyllodes tumors, also known as cystosarcoma phyllodes, are a rare type of breast cancer that involves tumor cells that grow in a leaf-like pattern. This type tends to grow quickly, but is usually localized to the area of the breast and does not spread around the body.
Molecular Subtypes of Breast Cancer
There are several molecular subtypes of breast cancer according to the type of genes that the cancer cells express. These include:
- Luminal A: hormone receptor positive, HER2 negative and low levels of Ki-67 protein. This subtype tends to grow slowly and is associated with a good prognosis.
- Luminal B: hormone receptor positive and high levels of Ki-67 protein. This subtype tends to grow more quickly than luminal B and is associated with a poorer prognosis.
- Triple-negative: hormone receptor negative and HER2 negative: This subtype is common in women with a mutation in the BRCA1 gene.
- HER2: hormone receptor negative and HER2 positive: This subtype tends to grow more quickly than luminal subtypes and has a poor prognosis without treatment, but targeted therapies are improving treatment outcomes for affected individuals.
- Normal-like: hormone receptor positive, HER2 negative and low levels of Ki-67 protein. This subtype is similar to luminal A but has a slightly worse prognosis.