Types of Breast Cancer

Charles Weaver MD
Medical Oncologist, Medical Advisor

Cancers of the breast are not all the same. The cells in the breast where a breast cancer begins determines how the cancer behaves and what treatments are most effective. To determine the type of breast cancer you have doctors look at the cells taken from a biopsy under a microscope and evaluate features of those cells at the molecular level to define your specific breast cancer type which determines your treatment.

Breast cancer can begin in the cells lining the milk ducts, the cell in the lobules where milk is produced or rarely in the connective tissue cells made up of fat, muscle, and blood vessels.

Ductal Carcinoma is the most common type of breast cancer and begins in the ducts that carry breast milk from the lobules, where it’s made, to the nipple. Ductal carcinoma can remain within the ducts as a noninvasive cancer (ductal carcinoma in situ), or it can break out of the ducts (invasive ductal carcinoma). Some subtypes of breast cancer are named for the way the cells appear under the microscope. Subtypes include tubular, mucinous, medullary and papillary. The subtype may provide your doctor with some clues about your prognosis and how your cells will respond to treatment.

Lobular Carcinoma starts in the lobules of the breast, where breast milk is produced. When it breaks out of the lobules, it’s considered invasive lobular carcinoma.

Connective tissues. Cancer that begins in the connective tissue are called sarcoma. Sarcomas in the breast include phyllodes tumor and angiosarcoma and are uncommon.

  • Estrogen receptor (ER) positive breast cancers have receptors that allow them to use the hormone estrogen to grow and treatment with anti-estrogen hormone (endocrine) therapies can block the growth of the cancer cells.
  • Progesterone receptor (PR) positive breast cancers sensitive to progesterone, and the cells have receptors that allow them to use this hormone to grow. Treatment with endocrine therapy blocks the growth of the cancer cells.
  • Hormone receptor (HR) negative breast cancers lack both estrogen and progesterone receptors and are not treated with hormone therapy.

Genetic makeup of your breast cancer cells personalizes treatment.

Individual DNA changes within cancer cells increasingly determine treatment options. By analyzing the cancer growth causing genes of cancer cells, doctors can personalize cancer treatment with precision cancer medicines and immunotherapy.

  • HER2Cancer cells that have too many copies of the HER2 gene (HER2-positive cancers) produce too much of the growth-promoting protein called HER2. Targeted therapy drugs are available to shut down the HER2 protein, thus slowing the growth and killing these cancer cells.
  • Other tumor markers.Researchers are studying ways to interpret the genetic makeup of tumor cells. Doctors hope this information can be used to predict which cancers will spread and which may need aggressive treatments. That way, women with relatively low-risk breast cancers may avoid aggressive treatments.

A combination of the tissue, molecular, and genetic characteristics of your breast cancer ultimately define your type of breast cancer and treatment options.

Ductal Carcinoma in situ (DCIS) is a very early form of breast cancer. It’s the most common type of noninvasive breast cancer. DCIS is classified as low, intermediate, or high. Grades are based on what the cells look like under a microscope. A lower grade means DCIS looks more like normal breast cells. The higher the grade, the more it looks different from normal cells.

Lobular Carcinoma in situ is a condition that is not breast cancer or a precancer. Often, it does not become invasive cancer if it’s not treated. Atypical lobular hyperplasia is also a condition that is not cancer. It’s when there are more cells than usual in your breast’s lobules. The extra cells are abnormal. Both LCIS and ALH raise your risk of getting breast cancer in the future. If you have been diagnosed with either of them, talk with your doctor.

Invasive Ductal Carcinoma
Invasive ductal carcinoma (IDC) is the most common type of breast cancer, affecting about 80% of people who are diagnosed. “Invasive” means the cancer is able to spread outside of the milk duct where it started. There are also five main molecular subtypes of invasive breast cancer based on the genes in the cancer tumor. The molecular subtype of a breast cancer can affect how the cancer is treated.

Invasive Lobular Carcinoma (ILC) starts in the lobules and spreads to tissue around them. It is the second most common form of breast cancer. About 10% of invasive breast cancers are this type. ILC

ER/PR Positive Breast Cancer
Breast cancer can have receptors for estrogen, progesterone, both, or neither.  ER/PR positive cancers can be treated by blocking estrogen and progesterone from plugging into receptors. This cuts the cancer off from hormones that could help it grow.

Her2 Positive Breast Cancer
About 1 out of every 5 breast cancers tests positive for human epidermal growth factor receptor 2 (HER2).  The HER2 protein helps control the growth of healthy breast cells. HER2/neu is a gene that acts like an on/off switch to make HER2. In HER2 positive breast cancer there’s either extra copies of the HER2/neu gene, or too much HER2. Precision cancer medicines that target HER2 are used for treatment.

HER2 Positive Breast Cancer
HER2-negative cancers make up many kinds of cancers. A lot of them have low levels of the HER2 protein, so they’re called HER2-low breast cancer. About half of all breast cancers are HER2-low. In August 2022 the U.S. Food and Drug Administration approved the first treatment specifically for HER2-low metastatic breast cancer.

Around 15% of breast cancers don’t have receptors for estrogen, progesterone, or HER2. These cancers are referred to as “triple negative breast cancers” and cannot be treated with hormone therapy.

Inflammatory Breast Cancer
This rare type makes up less than 5% of all breast cancers. Its symptoms are different from those of other breast cancers. Cancer cells block lymphatic vessels in your breast (similar to blood vessels, except they carry lymphatic fluid). This causes the skin to swell, turn red, and thicken. Parts of your breast might look like the skin of an orange. Inflammatory breast cancer can spread quickly. A rare type of breast cancer, inflammatory breast cancer develops rapidly and causes red, swollen, and tender breasts. Cancer cells block lymphatic vessels in the skin covering the breast, resulting in a characteristic red, swollen appearance.

Phyllodes Tumor of the Breast
These rare tumors grow in the breast’s connective tissue. They’re more common in women who have an inherited condition called Li-Fraumeni syndrome. Only 1 in 4 phyllodes tumors are cancer. The rest are noncancerous (benign).

This cancer grows in the lining of blood vessels and lymph vessels. Angiosarcomas form in the skin, breast, liver, and spleen. They’re most likely to affect people over 70.

Breast Papilloma
A breast papilloma is a small, wartlike growth in the breast’s milk ducts. It’s also called intraductal papilloma. This benign (not cancer) condition can cause a clear or bloody discharge from the nipple. You also may feel a small lump behind or next to the nipple. Having 1 papilloma does not raise your breast cancer risk. If you have several of them, you may be at higher risk.

Metaplastic Carcinoma
Metaplastic carcinoma is a rare type of invasive breast cancer. It has a mix of 2 or more kinds of breast cancer cells, usually carcinoma and sarcoma. It’s also called metaplastic breast cancer. Metaplastic means cancer that starts in cells that have changed into another kind of cell.

Breast Sarcoma
Breast sarcoma is a very rare form of breast cancer. It does not start in the lobes or ducts. Instead, a tumor can form in the connective or fibrous tissue around them. Only 1 out of every 100 cases of breast cancers are breast sarcoma.

Paget’s Disease
This rare type accounts for less than 5% of all breast cancers in the U.S. It grows in the nipple and the area around it (areola). The skin of your nipple and areola may get scaly, red, and itchy. Most women with Paget’s disease also have ductal or invasive breast cancer.

Metastatic breast cancer
Metastatic, advanced breast cancer, or stage 4 breast cancer is invasive cancer that has spread from the breast. It can spread to the skin, lymph nodes, or to other areas, such as the liver, lungs, or bones. Some people have metastatic cancer when they’re first diagnosed. More often, you get advanced breast cancer when the disease comes back somewhere else in the body, even after you had treatment.

Molecular Subtypes of Breast Cancer
Doctors are increasingly using genetic information about breast cancer cells to categorize breast cancers. The molecular subtype of an invasive breast cancer is based on the genes the cancer cells express, which control how the cells behave. Researchers have identified five main molecular subtypes of invasive breast cancer. The molecular subtype of an invasive breast cancer is based on the genes the cancer cells express, which control how the cells behave.

Luminal A breast cancer is estrogen and progesterone receptor-positive but HER2-negative. They have low levels of the protein Ki-67, which helps control how fast cancer cells grow. Luminal A cancers tend grow more slowly and have a good prognosis.

Luminal B breast cancer is estrogen receptor-positive and HER2-negative, and also has either high levels of Ki-67 (which indicate faster growth of cancer cells) or is progesterone receptor-negative.
Luminal B-like breast cancer Luminal B-like breast cancer is estrogen-receptor-positive and HER2-positive and has any level of Ki-67 and may be progesterone receptor-positive or progesterone receptor-negative. Luminal B cancers tend to grow faster than luminal A cancers and have a slightly worse prognosis.

HER2-positive breast cancer is estrogen receptor-negative and progesterone receptor-negative and HER2-positive. HER2-enriched cancers tend to grow faster than luminal cancers and can have a worse prognosis but can be successfully treated with precision cancer medicines targeting the HER2 protein.

Triple-negative or basal-like breast cancer is estrogen receptor-negative, progesterone receptor-negative, and HER2-negative. Triple-negative breast cancer is more common in people with a BRCA1 mutation younger women Black women Triple-negative breast cancer is considered more aggressive than either luminal A or luminal B breast cancer.

Charles Weaver MD

Medical Advisor