Breast cancer is a malignant area in the breast.

When it spreads into the surrounding breast tissue, it is called invasive breast cancer.

There are a number of types of breast cancer and how they develop is not completely understood.

Some breast cancers have a better chance of successful treatment than others.

Most breast cancers start in the milk ducts of the breasts (ductal cancers), others start in the lobules of the breast (lobular cancers). Cancers can develop slowly over years or more quickly over months. Breast cancer can spread to the lymph nodes which are the drainage system of the human body. In this way cancer cells can spread to other parts of the body, such as the lungs, bones and liver. Breast cancer can also spread through the bloodstream.

The risk of being diagnosed with breast cancer increases with age. Breast cancer is uncommon in women under 50. About 70 percent of women who are diagnosed with breast cancer and about 80 percent of women who die from it are 50 years or older.

Some women are at greater risk of breast cancer because there is a history of close family members having the disease. However, most women who develop breast cancer have no relatives with the disease. Even among women who do have relatives with breast cancer, most will never develop it.

Ductal carcinoma in situ or DCIS

Ductal carcinoma in situ is an early form of breast cancer that is contained within the breast duct and has not spread into the surrounding tissue. Although a small number of cases of DCIS are found because there are changes in the nipple, most cases are found through mammography screening. DCIS may show on the mammogram as small specks of calcium in the breast, called microcalcifications. Not all microcalcifications are caused by DCIS.

In BreastScreen Aotearoa, about 22 percent of detected cancers are DCIS.

DCIS can be low grade, intermediate or high grade. High grade means the cells are multiplying more rapidly, and the DCIS is more likely to progress to invasive cancer. It is not possible to predict which cases of DCIS will develop into invasive cancer.

DCIS is diagnosed the same way as invasive breast cancer. Treatment is offered to prevent the development of invasive breast cancer. The treatment options depend on the size and grade of the DCIS. If there is a small amount of low-grade DCIS, surgical removal of the areas is recommended, usually followed by radiotherapy. If there is a large area, or several areas, a mastectomy may be recommended. Removal of the lymph nodes is not recommended for women with small areas of DCIS alone who are not having reconstruction because of the risk of swelling in the area.

Making a decision about what to do about DCIS is difficult. Not all cases of DCIS develop into invasive cancer, but it is not possible to say which will and which will not. Low-grade DCIS may hide a higher grade DCIS or invasive cancer, or sometimes high-grade DCIS can hide an invasive cancer. The area of DCIS may be bigger than what is seen on the mammogram.

If a needle biopsy finds DCIS, an open surgical biopsy is needed to make sure no invasive cancer is present.

Some women with low-grade DCIS may choose not to have further treatment after surgery but wait and see. About 40 percent of cases of low grade DCIS progress to invasive diseases after 30 years. It is important that all options are discussed with the surgeon and breastcare nurse.