Cancer occurs when normal body cells get out of control, multiply and spread. These cells clump together to form a cancerous or malignant tumour, which can then grow and damage healthy parts of the body.

Breast cancer is a malignant tumour that starts in the milk-producing tissues of the breast. These tissues are called the ducts and lobules. When women breastfeed, the milk is made in the lobules and flows along the ducts to the nipple.

Breast cancer most commonly affects women, but it can also occur in men.

Cancer that starts in the breast is called primary breast cancer. Cancers that start elsewhere in the body may eventually spread to the breast, but this is rare.

The information in this part of the website is about primary breast cancer.

There are several different types, including:

Ductal carcinoma in situ (DCIS)

This is an early form of breast cancer that starts in a milk duct. The cancer is still inside the duct and hasn't spread outside it. This means it is a non-invasive form of breast cancer.

Invasive breast cancer

Breast cancer starts inside one of the ducts or lobules of the breast. If the cancer has started to spread outside a duct or lobule it is said to be invasive.

In nine out of 10 cases, invasive breast cancer starts in the ducts and is called ductal. In most other cases, invasive cancer starts in the lobules. About one in 10 invasive cancers don't show up on mammograms (breast X-rays), and this is more likely with lobular breast cancer.

Paget's disease of the breast

This is a rare, slow growing breast cancer that produces changes in the nipple. There may be a red, scaly rash, or the nipple may be inverted (pulled in). There may or may not be a lump. The nipple changes are always associated with an underlying cancer.

Inflammatory breast cancer

This is a rare, fast growing breast cancer that can be hard to diagnose. It may cause redness and swelling of the breast.

Lobular carcinoma in situ (LCIS)

Lobular carcinoma in situ is a breast condition linked to cancer. LCIS is not actually a cancer, but people who get it are five times more likely to develop invasive breast cancer in the future.