Once you've been diagnosed with breast cancer, your doctor will review your pathology report and results of any imaging tests to understand 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.

In what part of the breast did your cancer begin?

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.

  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).

• Milk-producing lobules. 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. 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 includ 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. Some subtypes of breast cancer are named for the way they appear under the microscope. Subtypes include tubular, mucinous, medullary and papillary. Your subtype gives your doctor some clues about your prognosis and how your cells may respond to treatment.
• 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.

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Feb. 06, 2015 See more In-depth