Breast cancer is the abnormal growth of the cells lining the breast lobules or ducts. 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.
This information has been prepared to help you understand more about early breast cancer. If you need information about secondary breast cancer (also called metastatic or advanced breast cancer), visit the Breast Cancer Network of Australia or Cancer Australia.
Topics on this page:
- The breasts
- Abnormal cells in the breast
- Invasive breast cancer
- Who gets breast cancer?
- What causes breast cancer?
Women and men both have breast tissue.
In women, breasts are made up of milk glands. A milk gland consists of:
- lobules – where milk is produced
- ducts – tubes that carry milk to the nipples.
In men, the development of the lobules is suppressed at puberty by testosterone, the primary male sex hormone.
Both female and male breasts also contain supportive 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 a key 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 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.
Abnormal cells in the breast
Some conditions involve abnormal cells in the breast, but are not invasive breast cancer.
Ductal carcinoma in situ (DCIS)
DCIS means that abnormal cells are contained within the ducts of the breast. This condition is considered non-invasive breast cancer. It can increase the risk of developing invasive breast cancer.
Lobular carcinoma in situ
Some women have abnormal cells that are contained within the lobules of the breast. This is called lobular carcinoma in situ (LCIS). This is not considered cancer. LCIS is very rare in men.
While LCIS increases the risk of developing breast cancer, most people with this condition will not develop breast cancer.
LCIS is usually detected during tests for other breast disorders. If you are diagnosed with LCIS, you will be monitored with regular screening mammograms or other types of breast imaging.
Invasive breast cancer
Most breast cancers are found when they are invasive. There are several types of invasive breast cancer.
Early breast cancer
In early breast cancer, the cancer has spread from the breast ducts or lobules into surrounding breast tissue. It may also have spread to lymph nodes in the armpit.
The most common types of early breast cancer are:
- invasive ductal carcinoma (IDC) – makes up about 80% of breast cancers
- invasive lobular carcinoma (ILC) – makes up about 10% of breast cancer cases.
Other types of invasive breast cancer include:
- locally advanced breast cancer
- secondary breast cancer (also known as advanced or metastatic breast cancer)
- inflammatory breast cancer
- Paget’s disease of the nipple.
Who gets breast cancer?
Apart from non-melanoma skin cancer, breast cancer is the most common cancer diagnosed in Australian women – it represents 28% of all cancers diagnosed in women. About 15,000 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 25% are diagnosed in women aged 70 and over.
About 120 men are diagnosed with breast cancer in Australia each year, and most of these men are over 50. Breast cancer in men makes up less than 1% of all breast cancers – only 1 in 838 men will be diagnosed before the age of 85.
What causes breast cancer?
In most people, the exact cause of breast cancer is unknown, but some factors can increase the risk. Most people diagnosed with breast cancer have no known risk factors, aside from getting older, which increases the risk in women and men.
Having risk factors does not necessarily mean that you will develop breast cancer.
In women, risk factors include:
- having several first-degree relatives, such as mother, father, sister or daughter, diagnosed with breast cancer and/or a particular type of ovarian cancer. However, most women diagnosed with breast cancer do not have a family history
- having a family member who has had genetic testing and has been found to carry a mutation in the BRCA1 or BRCA2 genes
- 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)
- long-term hormone replacement therapy (HRT) use.
In men, the risk is increased in those who have:
- several first-degree relatives (male or female) who have had breast cancer
- a relative diagnosed with breast cancer under the age of 40
- several relatives with ovarian or colon cancer
- a family member who has had genetic testing and has been found to carry 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).
Some lifestyle factors, such as being overweight, smoking, drinking alcohol and a lack of physical activity may also slightly increase the risk of breast cancer in both women and men.
Inherited breast cancer gene
Most people diagnosed with breast cancer do not have a family history of the disease. However, a small number of people have inherited a gene fault that increases their breast cancer risk.
Everyone inherits a set of genes from each parent, so they have two copies of each gene. Sometimes there is a fault in one copy of a gene. This fault is called a mutation.
The two most common gene mutations that are linked to breast cancer are on the BRCA1 and BRCA2 genes. Women in families with an inherited BRCA1 or BRCA2 change are at an increased risk of breast and ovarian cancers. Men in these families may be at an increased risk of breast and prostate cancers.
People with a strong family history of breast cancer can attend a family cancer clinic for tests to see if they have inherited a gene mutation. For more information about genetic testing, talk to your doctor or breast care nurse, or call Cancer Council 13 11 20.