What is breast cancer?

The breasts

Breasts are made up of:

• fat

• glandular tissue divided into lobes (each containing lots of lobules)

• a network of ducts or milk ducts

• connective tissue

The lobules produce milk for breastfeeding and connect to the ducts. The ducts spread from the lobes towards the nipple.

Men have breast tissue around the nipple area and can develop breast cancer, but this is rare.

Breast size and density

One breast is usually smaller than the other. Your breasts may feel different at different times of the month. It is common for breasts to feel lumpy just before your period.  

Younger women have more glandular tissue than fat in their breasts, making them denser than older women's breasts.

Your breasts also change during pregnancy. You may notice that they become bigger and feel more tender.

After your periods stop (menopause) fat gradually replaces the glandular tissue, which is less dense.

Lymph nodes

There is a network of lymph glands close to the breast. These are also called lymph nodes. They are part of the ​lymphatic system​ that runs throughout the body.

The lymph nodes and lymph vessels contain a yellow fluid called lymph that flows through the lymphatic system. It collects waste products and drains them into veins. 

Cancer cells that have broken away from the breast tissue can be carried by the lymph fluid to nearby lymph nodes. If you have cancer, but no cancer cells in any of your lymph glands, your cancer is less likely to have spread elsewhere in your body.

The diagram below shows the network of lymph glands around the breast.

The lymph glands in the armpit are called the axillary lymph glands. There are also lymph nodes in the centre of the chest, close to the breastbone. These are called the internal mammary chain.

Where breast cancer starts

Breast cancer cancer can start in different parts of the breast. It usually starts in the milk ducts or the lobules. It can be invasive or non invasive (in situ). Invasive breast cancer means that the cancer cells have spread outside the ducts or lobules where they started and into the surrounding breast tissue.

Invasive breast cancers

There are different types of invasive breast cancer. The most common type is now called invasive breast cancer. It used to be called invasive ductal carcinoma. Most invasive breast cancers have no special features and are also called ‘No Special Type’ (NST). Invasive lobular breast cancer is the second most common type. Doctors also call it invasive lobular carcinoma. There are also other rarer types of invasive breast cancer.

Non invasive breast cancers

Carcinoma in situ means that cells in the lining of the ducts or lobules have started to turn into cancer cells. But they have not started to spread into the surrounding breast tissue. The 2 types are:

• ductal carcinoma in situ (DCIS)

• lobular carcinoma in situ (LCIS)

Find out more about the different types of breast cancer

Who gets breast cancer?

Breast cancer is more common in women than men. Around 57,900 women and around 400 men are diagnosed with breast cancer in the UK each year. 

1 in 7 women in the UK develop breast cancer during their lifetime. It is more common in older women. 

Your risk of breast cancer depends on several factors. These include your age, family history and other factors such as obesity and smoking.

Read about risk factors for breast cancer

How common is breast cancer?

Breast cancer is the most common cancer in the UK. Around 58,300 people are diagnosed with breast cancer every year in the UK. That is around 160 people a day. 

15 out of 100 (15%) newly diagnosed cancers in the UK are breast cancer.