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HealthInfo Canterbury

About breast cancer

Mō te ūtaetae

This page has links to information in te reo Māori.


breast anatomyBreast cancer is a cancer that grows in your breast tissue.

Your breasts are made up of different types of tissue, including lobules (which hold your milk-producing glands), ducts (which carry the milk to the nipple), fatty tissue, blood vessels, lymph vessels, and nerves.

Breast cancer happens when cells in the ducts or lobules start to grow out of control, in a way that can spread throughout your breast and then to other parts of your body.

Breast cancer is the most common cancer in New Zealand women – around 3000 are diagnosed each year. It mostly affects women aged over 50, but it can also happen in young women, so it's important to get to know your own breasts and be breast aware from the age of 20.

Men can also get breast cancer, but this is very rare – only around 20 New Zealand men a year are diagnosed with breast cancer.

What are the different types of breast cancer?

Breast cancer is categorised in several different ways. The first depends on whether it has spread or not. If the cancer stays inside the lobule or duct it grows in it's called carcinoma in situ. This has a good outlook and is relatively easy to treat. But if the cancer cells have spread beyond the original site into blood and lymph vessels or glands it's called invasive cancer.

The second way it's categorised is by grade. This depends on how the cancer cells are growing.

The pathologist, who looks at the cells under a microscope, decides what grade the cancer is.

The third category is the stage of cancer, which describes things about how big the cancer is, and where it is. The stages are based on a system called TNM.

The surgeon decides what stage the cancer is, and uses it to help plan treatment.

For example, a cancer might be described as "high-grade invasive ductal carcinoma T1 N1 M0". This would mean it was a fast-growing cancer that had started in the duct but spread outside it. It would also be small (T1), involve only a small number of nodes (N1) and not have spread to other parts of the body (M0).

Another cancer might be described as "low-grade ductal carcinoma in situ T1 N0 M0". This would mean it was a slow-growing, small cancer, still confined inside a duct and had not spread to any nodes or any other part of the body.

Finally, cancer is categorised depending on the receptors on the cell surfaces. Receptors are areas that respond to certain hormones or proteins and can make the cancer grow more quickly. For example, some breast cancer cells have receptors for the hormone estrogen or for the protein human epidermal growth factor (HER2). Treatment for the cancer will differ according to these receptors.

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On the next page: Am I at risk of breast cancer?

Written by HealthInfo clinical advisers. Endorsed by oncoplastic breast and general surgeon, Canterbury DHB. Page created May 2018.


Page reference: 393199

Review key: HIBCA-57360