What Type of Breast Cancer Is Most Likely to Metastasize?

Breast cancer is the most frequently diagnosed life-threatening cancer in women and the leading cause of cancer deaths among women. Breast cancer types are divided into two main categories:

1. Noninvasive breast cancer
2. Invasive breast cancer

Noninvasive breast cancer

Noninvasive cancer (also called carcinoma in situ or precancer) forms within the milk ducts or lobules in the breast. Although healthy breast tissue is not yet affected, the cancer may progress at any time and immediate treatment is crucial. 

There are two main types of noninvasive breast cancer:

1. Ductal carcinoma in situ (DCIS): Considered the most common, DCIS starts in the milk ducts of the breast but hasn’t yet invaded the surrounding tissues. Patients with DCIS generally show no signs or symptoms, although a small number of patients may have a lump in the breast or discharge coming out of the nipples. This noninvasive breast cancer has the potential to develop into invasive breast cancer at any time.
2. Lobular carcinoma in situ (LCIS): An uncommon condition in which abnormal cells form in the lobules (lining of the milk glands) of the breast but haven’t yet invaded the wall of the lobules. As time passes, having LCIS increases the risk of developing invasive breast cancer. 

Invasive breast cancer

Invasive breast cancer is breast cancer that has spread outside the ducts and lobules into the surrounding tissues. Types of invasive breast cancer include:

• Invasive ductal carcinoma (infiltrating ductal carcinoma): The most common type of breast cancer, making up 80% of all breast cancer diagnoses. The cancer develops in the milk duct, then starts invading the fibrous or fatty tissue of the breast outside the duct. Once the cancer has spread to the surrounding tissue, it starts metastasizing to other organs by gaining entry through the lymph vessels.
• Invasive lobular carcinoma: The second most common type of breast cancer. The cancer develops in the milk-producing lobules and spreads to the adjacent healthy tissues by breaking through the lining of the lobules. Over time, it has the potential to spread to the lymph nodes and other areas of the body.
• Paget’s disease of the nipple: A rare condition associated with breast cancer that causes eczema-like changes in the skin of the nipple and extends to the areola (area of the darker skin surrounding the nipple). Most people with Paget’s disease have underlying ductal breast cancer, either in situ (in its original place) or, less commonly, invasive breast cancer
• Inflammatory breast cancer (IBC): A rare and aggressive type of breast cancer that makes about one to five percent of cases. The cells block the lymph nodes in the breast so that the lymph vessels can’t properly drain. This condition causes the breast to swell, look red and appear pitted and thick like an orange peel.
• Phyllodes tumors of the breast: Very rare types of fibroepithelial tumors that grow quickly in the connective tissue or stroma of the breast tissue. Most phyllodes tumors are benign, but some may be malignant.
• Locally advanced breast cancer: A type of invasive breast cancer that is large and has spread beyond the breast to nearby areas such as the skin, chest wall or muscle and may have extensive local lymph node involvement.
• Metastatic breast cancer: Also known as stage IV or secondary breast cancer. Metastatic breast cancer is an advanced stage where the cancer has spread from the breast to distant regions of the body such as the bones, lungs or liver.

The three main subtypes of breast cancer are:

1. Hormone receptor-positive breast cancer: Hormone receptor-positive breast cancer cells need female hormones (estrogen and progesterone) to grow and reproduce. About 80% of all breast cancers are estrogen-positive and 65% are progesterone-positive.
2. Human epidermal growth factor receptor 2 (HER2)-positive breast cancer: HER2-positive breast cancer cells have an excessive amount of the protein HER2 on the surface. Excess HER2 receptors promote the growth of the cancer cells.
3. Triple-negative breast cancer: This rare type of breast cancer lacks all three of the receptors (estrogen, progesterone and HER2) that are commonly found in the breast cancer cells. Triple-negative breast cancer tends to grow and spread more quickly than other types of breast cancer.