The type of breast cancer you have helps determine the best approach to treating the disease. Get the facts on types of breast cancer and how they differ.

By Mayo Clinic staff

Once you’ve been diagnosed with breast cancer, your doctor works to find out the specifics of your tumor. Using a tissue sample from your breast biopsy or using your tumor if you’ve already undergone surgery, your medical team determines your breast cancer type. This information helps your doctor decide which treatment options are most appropriate for you.

Here’s what’s used to determine your breast cancer type.

Is your cancer invasive or noninvasive?

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Lobular carcinoma in situ

Whether your cancer is invasive or noninvasive helps your doctor determine whether your cancer may have spread beyond your breast, which treatments are more appropriate for you, and your risk of developing cancer in the same breast or your other breast.

• Noninvasive (in situ) breast cancer. In situ breast cancer refers to cancer in which the cells have remained within their place of origin — they haven’t spread to breast tissue around the duct or lobule. The most common type of noninvasive breast cancer is ductal carcinoma in situ (DCIS), which is confined to the lining of the milk ducts. The abnormal cells haven’t spread through the duct walls into surrounding breast tissue. Doctors sometimes refer to this type of cancer as stage 0 cancer.
• Invasive breast cancer. Invasive (infiltrating) breast cancers spread outside the membrane that lines a duct or lobule, invading the surrounding tissues. The cancer cells can then travel to other parts of your body, such as the lymph nodes. If your breast cancer is stage I, II, III or IV, you have invasive breast cancer.

In what part of the breast did your cancer begin?

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Breast anatomy

The type of tissue where your breast cancer arises determines how the cancer behaves and what treatments are most effective. Parts of the breast where cancer begins include:

• Milk ducts. Ductal carcinoma is the most common type of breast cancer. This type of cancer forms in the lining of a milk duct within your breast. The ducts carry breast milk from the lobules, where it’s made, to the nipple.
• Milk-producing lobules. Lobular carcinoma starts in the lobules of the breast, where breast milk is produced. The lobules are connected to the ducts, which carry breast milk to the nipple.
• Connective tissues. Rarely breast cancer can begin in the connective tissue that’s made up of muscles, fat and blood vessels. Cancer that begins in the connective tissue is called sarcoma. Examples of sarcomas that can occur in the breast include phyllodes tumor and angiosarcoma.

How do your cancer cells appear under a microscope?

When a sample of your breast cancer is examined under a microscope, here’s what the pathologist looks for:

• Cancer cells with unique appearances. Invasive ductal carcinoma cells sometimes take on unique appearances that can be seen with a microscope. Subtypes of invasive ductal carcinoma that describe how the cells appear include tubular, mucinous, medullary and papillary.
• The degree of difference between the cancer cells and normal cells. How different your cancer cells look from normal cells is called your cancer’s grade. Breast cancers are graded on a 1 to 3 scale, with grade 3 cancers being the most different looking and considered the most aggressive.

Are your cancer cells fueled by hormones?

Some breast cancers are fueled by your body’s naturally occurring female hormones — estrogen and progesterone. The breast cancer cells have receptors on the outside of their walls that can catch specific hormones that circulate through your body. Knowing your breast cancer is dependent on hormones gives your doctor a better idea of how to cut off the fuel supply for your cancer cells.

Hormone status of breast cancers includes:

• Estrogen receptor (ER) positive. This type of breast cancer relies on estrogen to help it grow.
• Progesterone receptor (PR) positive. This type of breast cancer relies on progesterone to help it grow.
• Hormone receptor (HR) negative. This type of cancer doesn’t have hormone receptors, so it doesn’t need hormones to help it grow.

With ER positive or PR positive breast cancer, hormone-blocking medications, such as tamoxifen, may be an option to slow the cancer’s growth. HR negative cancers don’t respond to hormone-based therapy.

What is the genetic makeup of your breast cancer cells?

Doctors are just beginning to understand how the individual DNA changes within cancer cells might one day be used to determine treatment options. A cell’s DNA is full of instructions (genes) that tell it how to behave. By analyzing the genes, doctors hope to be able to find ways to target specific aspects of the cancer cells to kill them.

Laboratory testing can reveal certain genes in your cancer cells, such as:

• HER-2 gene. Cancer cells that have too many copies of the HER-2 gene produce too much of the growth-promoting protein called HER-2. Medications are available to shut down the HER-2 gene, thus cutting the cancer cells off from their energy supply.
• Other genes. 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. Tests that analyze the genetic makeup of breast cancers are available, but aren’t recommended in all situations. Ask your doctor whether this type of test might be helpful in your case.

Source: http://www.mayoclinic.com/health/breast-cancer/HQ00348