What are the four types of breast cancer?

The four main types of breast cancer are preinvasive breast cancer (DCIS or LCIS), invasive breast cancer (IDC or ILC), inflammatory breast cancer, and metastatic breast cancer.

Preinvasive cancer: Ductal Carcinoma In Situ or Lobular Carcinoma In Situ

Ductal Carcinoma In Situ (DCIS) and Lobular Carcinoma In Situ (LCIS) are very early, noninvasive breast cancers (also called stage 0 cancers) where abnormal cells are found in the lining of the breast milk duct (DCIS) or lobules of the breast (LCIS). The abnormal cells have not spread outside of these areas into the surrounding breast tissue. Preinvasive DCIS and LCIS are highly treatable and seldom become invasive cancer.

Invasive Breast Cancer: Invasive Ductal Carcinoma and Invasive Lobular Carcinoma

Invasive ductal carcinoma (IDC) and invasive lobular carcinoma (ILC) are the most common types of invasive breast cancer. Invasive means cancer has spread from the original site through the bloodstream and lymph nodes to other areas, like nearby breast tissue, lymph nodes, or elsewhere.

Invasive ductal carcinoma is the most common type of breast cancer—accounting for roughly 70 to 80 percent of all cases. IDC starts in a milk duct (the tubes in the breast that carry milk to the nipple) and grows into other parts of the breast. With time, it may spread further, or metastasize, to other parts of the body.

Invasive lobular carcinoma (ILC) is the second most common type, accounting for roughly 5 to 10 percent of all breast cancers. ILC starts in lobules (where breast milk is made) and then spreads into the nearby breast tissue. Like IDC, it may metastasize and spread to other parts of the body. This cancer is harder to detect on mammograms than IDC and one in five women with ILC have both breasts affected.

Inflammatory Breast Cancer (IBC)

Inflammatory breast cancer is aggressive and fast-growing breast cancer in which cancer cells infiltrate the skin and lymph vessels of the breast. There is often no lump or distinct tumor that can be felt and isolated within the breast, and symptoms don’t usually appear until the lymph vessels become blocked by the breast cancer cells.

Metastatic Breast Cancer

Metastatic breast cancer is breast cancer that has spread to other parts of the body, such as the lungs, liver, bones, or brain. It is also classified as Stage 4 breast cancer.

Other types of breast cancer can occur, although these are not so common:

• Medullary Carcinoma Medullary carcinoma: A rare subtype of IDC accounting for about 3-5% of all cases of breast cancer that can occur at any age, but usually affects women in their late 40s and early 50s, and those with a BRCA1 mutation.
• Phyllodes tumors of the breast: These are rare breast tumors that start in the connective (stromal) tissue of the breast and are most common in women in their 40s, and in women with Li-Fraumeni syndrome (a rare, inherited genetic condition). Most are benign (not cancer), but about 1 out of 4 of these tumors are malignant (cancer).

Paget's disease of the nipple is a rare condition associated with breast cancer. It causes eczema-like changes to the skin of the nipple and the area of darker skin surrounding the nipple and is usually a sign of breast cancer in the tissue behind the nipple. It affects about 1 to 4% of women with breast cancer. It can also affect men, but this is extremely rare.

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What are the subtypes of breast cancer?

There are three main subtypes of breast cancer:

• Hormone receptor-positive breast cancer
• HER2-positive breast cancer
• Triple-negative breast cancer.

Hormone receptor-positive breast cancer needs female hormones (estrogen and/or progesterone) to grow and reproduce. Hormone receptor-positive breast cancer accounts for about two-thirds of breast cancers.

HER2-positive breast cancer cells have too much of a protein called human epidermal growth factor receptor 2 on the surface of the cancer cells. These excess HER2 receptors promote the growth of cancer cells. HER2-positive breast cancers may be either hormone receptor-positive or negative. Most HER2-positive breast cancers are treated with a combination of treatments that includes the drug Herceptin (trastuzumab) for 12 months, which specifically targets HER2-positive breast cancer. Hormone-blocking therapy may also be recommended if the breast cancer is also hormone receptor-positive.

Triple-negative breast cancer is cancer that does not have any of the three receptors commonly found on breast cancer cells (ie, estrogen, progesterone, or HER2). Around 15% of breast cancers are triple-negative.