Breast cancer

Breast cancer is the abnormal growth of the cells lining the breast ducts or lobules. These cells grow uncontrollably and have the potential to spread to other parts of the body. Both women and men can develop breast cancer, although breast cancer is rare in men.

I went for an ultrasound and while they were doing it, people just kept coming in and I thought, ‘Oh, okay, everyone’s taking a lot of interest in this.’ The biopsies then confirmed that it was cancer.    — Read more of Anne’s story

This section covers early and locally advanced breast cancer (cancer that hasn’t spread beyond the breast tissue and nearby lymph nodes). Invasive breast cancer that has spread further is called advanced or metastatic. 

If you are looking for information about advanced breast cancer, inflammatory breast cancer or Paget’s disease of the nipple, call Cancer Council 13 11 20, or visit the Breast Cancer Network of Australia or Cancer Australia.

Learn more about:

• The breasts
• What is invasive breast cancer?
• What is carcinoma in situ?
• What causes breast cancer?
• Who gets breast cancer?

The breasts

Women and men both have breast tissue.

In women, breasts are mostly made up of lobes, lobules and ducts:

• Lobes – Each breast is divided into 12−20 sections called lobes.
• Lobules − Each lobe contains glands that produce milk. These milk glands are called lobules.
• Ducts − The lobes and lobules are connected by fine tubes called ducts. The ducts carry milk to the nipples.

In men, breast tissue has ducts but few or no lobes and lobules.

Both female and male breasts also contain fibrous and fatty tissue. Some breast tissue extends into the armpit (axilla). This is known as the axillary tail of the breast.

Breast cancer and the lymphatic system

The lymphatic system is an important part of the immune system.

It protects the body against disease and infection. It is made up of a network of thin tubes called lymph vessels that are found throughout the body. Lymph vessels connect to groups of small, bean-shaped structures called lymph nodes or glands.

Lymph nodes are found throughout the body, including in the armpits, breastbone (sternum), neck, abdomen and groin. The lymph nodes in the armpit (axillary lymph nodes) are often the first place cancer cells spread to outside the breast. During surgery for breast cancer (or, sometimes, in a separate operation), some or all of the lymph nodes will be removed and examined for cancer cells. For more on this kind of surgery, see Removing lymph nodes.

What is invasive breast cancer?

Most breast cancers are found when they are invasive. Invasive breast cancer means the cancer has spread from the breast ducts or lobules into the surrounding breast tissue.

The main types of invasive breast cancer are:

• invasive ductal carcinoma (IDC) – starts in the ducts and accounts for about 80% of breast cancers
• invasive lobular carcinoma (ILC) – starts in the lobules and makes up about 10% of breast cancers.

Less common types include inflammatory breast cancer and Paget’s disease of the nipple.

What is carcinoma in situ?

Sometimes tests find abnormal cells in the breast known as carcinoma in situ. These cells usually do not cause any symptoms and cannot spread to the lymph nodes or around the body as invasive breast cancer cells can. However, they may eventually turn into invasive breast cancer. There are two main types of carcinoma in situ in the breast:

Ductal carcinoma in situ (DCIS) – abnormal cells in the ducts of the breast. DCIS is considered non-invasive breast cancer and usually develops into invasive breast cancer over time. In most cases, DCIS is treated in the same way as early invasive breast cancer (see Treatment).

Lobular carcinoma in situ (LCIS) – abnormal cells in the lobules of the breast. This is not cancer, but increases the risk of developing cancer in either breast. However, most women with LCIS won’t develop breast cancer. If you have LCIS, you will usually have regular screening mammograms or other scans. Some less common types of LCIS may need surgery.

DCIS and LCIS are very rare in men.

What causes breast cancer?

In most people, the exact cause of breast cancer is unknown, but some factors can increase the risk. Most people with breast cancer have no known risk factors, aside from getting older. Having risk factors does not necessarily mean you will develop breast cancer.

In women, risk factors include:

• older age
• a strong family history, with several first-degree relatives (e.g. mother, sister) diagnosed with breast cancer and/or a particular type of ovarian. However, most women diagnosed with breast cancer do not have a family history
• inheriting a mutation in the BRCA1 or BRCA2 genes − more common with Ashkenazi Jewish heritage
• a previous diagnosis of breast cancer or ductal carcinoma in situ (DCIS)
• a past history of particular non-cancerous breast conditions, such as lobular carcinoma in situ (LCIS) or atypical ductal hyperplasia (abnormal cells in the lining of the milk ducts)
• regularly drinking alcohol
• being overweight after menopause
• a lack of physical activity
• having had radiation therapy to the chest for Hodgkin disease, especially if diagnosed under 30
• long-term hormone replacement therapy (HRT) use (slight increase in breast cancer risk).

Having children and breastfeeding can both slightly reduce breast cancer risk.

In men, risk factors include:

• older age
• a strong family history, with several first-degree relatives (male or female) who have had breast cancer; a relative diagnosed with breast cancer under the age of 40; or several relatives with ovarian or colon cancer
• inheriting a mutation in the BRCA1 or BRCA2 genes
• a rare genetic syndrome called Klinefelter syndrome – men with this syndrome have three sex chromosomes (XXY) instead of the usual two (XY).

Who gets breast cancer?

Apart from non-melanoma skin cancer, breast cancer is the most common cancer found in Australian women – it represents 28% of all cancers diagnosed in women. About 17,000 women are diagnosed with breast cancer each year, and one in eight will be diagnosed by the age of 85.

Although breast cancer can occur at any age, it is more common in women over 40. Almost 70% of breast cancers are diagnosed in women aged 40–69, and about 25% are diagnosed in women aged 70 and over. In rare cases, women are diagnosed during pregnancy.

About 140 men are diagnosed with breast cancer in Australia each year, and most of these men are over 50. Resources are available for men diagnosed with breast cancer – visit Cancer Australia’s website at breastcancerinmen.canceraustralia.gov.au.