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What is breast cancer?

Cancer is a condition that causes cells in the body to grow out of control. These cells form growths called tumours. Breast cancer is cancer that forms in breast tissue. Breast tissue is not only in your breasts. It goes all the way up to your collarbone and under your armpit. Everyone has breast tissue – people of all ages, races and genders.

In the UK, 1 in 7 women will be diagnosed with breast cancer in their lifetime. 

Around 55,500 women and around 400 men are diagnosed with breast cancer each year in the UK. 

If breast cancer is diagnosed early, it can be treated successfully. That is why we want to tell you about breast cancer, and encourage you to check your chest every month.

What even are Breasts?

When we talk about ‘breasts’ we mean the breast tissue in the chest area. You might call this area your breasts, boobs, pecs or chest. To understand breast cancer, it helps to understand a bit about the chest area. Breast tissue is different in women and men, but there are some similarities.

For example, all breast tissue contains fat and lymph vessels.

Primary breast cancer

Primary breast cancer is breast cancer that has not spread outside the breast or the lymph nodes (glands in your armpits). There are several different types of primary breast cancer. It can be diagnosed at different stages. Breast cancer is staged from stage 1 to stage 4. Primary breast cancer is different from secondary breast cancer. Secondary breast cancer is when breast cancer has spread to other parts of the body. We have more information about secondary breast cancer below.

Secondary breast cancer

Secondary breast cancer is when breast cancer spreads from the breast and lymph nodes (glands in your armpits) to other parts of the body. When cancer spreads to other parts of the body, it can form another tumour. This is called secondary cancer.

Secondary cancer is also called:

  • Stage 4 cancer
  • Metastatic cancer
  • Metastasis or metastases
  • Advanced breast cancer

Breast cancer can spread to many parts of the body. The most common parts are:

  • Bones
  • Lungs
  • Liver
  • Brain

If breast cancer spreads to other parts of the body, it is still called breast cancer. For example, breast cancer that spreads to the bone is called secondary breast cancer in the bone.

Secondary breast cancer can be treated, but not cured. Treatment for secondary breast cancer helps with symptoms and stops the cancer from spreading further. If someone has secondary breast cancer, they will always have it. Breast cancer specialists will talk to the person about the different ways they can manage their symptoms.

A person living with secondary breast cancer will be involved in making decisions about their treatment and care. It’s important these decisions are right for the individual.

Our friends at Breast Cancer Now have more information about secondary breast cancer.


DCIS means Ductal Carcinoma in Situ. It is the earliest form of breast cancer. DCIS is when the cancer cells are still inside the parts of the breast where they first formed. These parts are called lobules or ducts. In DCIS, “in situ’means the cancer cells have stayed in the lobules or ducts. DCIS might also be called:

  • Non-invasive breast cancer
  • Pre-invasive breast cancer
  • Pre-cancerous change
  • Intra ductal breast cancer
  • Ductal intraepithelial neoplasia (DIN)
  • Stage 0 breast cancer

Invasive breast cancer

Invasive breast cancer is the most common type of breast cancer. In the past it was also called invasive ductal carcinoma. Invasive breast cancer means that the cancer cells have grown through the lining of the ducts into the surrounding breast tissue. Invasive breast cancer starts as DCIS, but not every DCIS will turn into invasive breast cancer. 

We do not know which DCIS cells will become invasive breast cancer, and which won’t. Most cases of DCIS are treated because it can become invasive breast cancer in the future. DCIS is an early form of breast cancer and it can be cured with treatment.

It is always important to contact your GP if you notice any changes to your chest that are unusual for you. The earlier breast cancer is found, the better.

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We updated this information in April 2024. We will look at it again in April 2027.

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