- The breasts
- What is breast cancer?
- What are the risk factors?
- What are the symptoms of breast cancer?
- How common is breast cancer?
- Information reviewed by
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.
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. 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.
This website information only 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 Breast Cancer Network Australia or Cancer Australia.
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.
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.
Breast cancers are also categorised according to whether they are sensitive to hormones (hormone receptor status), have high levels of growth factors (HER2 positive) or are none of these (triple negative).
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 cancer. 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).
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.
Some people have no symptoms and the cancer is found during a screening mammogram (a low-dose x-ray of the breast) or a physical examination by a doctor. If you do have symptoms, they could include:
- a lump, lumpiness or thickening, especially if it is in only one breast
- changes in the size or shape of the breast
- changes to the nipple, such as a change in shape, crusting, sores or ulcers, redness, a clear or bloody discharge, or a nipple that turns in (inverted) when it used to stick out
- changes in the skin of the breast, such as dimpling or indentation, a rash, a scaly appearance, unusual redness or other colour changes
- swelling or discomfort in the armpit
- persistent, unusual pain that is not related to your normal monthly menstrual cycle, remains after your period and occurs in one breast only.
Most breast changes aren’t caused by cancer. However, if you have symptoms, see your doctor without delay.
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.
This website page was last reviewed and updated October 2019
Information last reviewed: Prof Christobel Saunders, Professor of Surgical Oncology and Head, Division of Surgery, The University of Western Australia, and Consultant Surgeon, Royal Perth, Fiona Stanley and St John of God Subiaco Hospitals, WA; Dr Marie-Frances Burke, Radiation Oncologist, Medical Director, Genesis CancerCare Queensland, QLD; Kylie Campbell, Breast Care Nurse and Clinical Lead, Murraylands, McGrath Foundation, SA; Carmen Heathcote, 13 11 20 Consultant, Cancer Council Queensland, QLD; Annmaree Mitchell, Consumer; Sarah Pratt, Nurse Coordinator, Breast Service, Peter MacCallum Cancer Centre, VIC; Dr Wendy Vincent, Breast Physician, Chris O’Brien Lifehouse and Royal Hospital for Women, Randwick, NSW, and Clinical Director BreastScreen NSW, Royal Prince Alfred Hospital, NSW; A/Prof Nicholas Wilcken, Director of Medical Oncology, Westmead Hospital, and Co-ordinating Editor, Cochrane Breast Cancer Group, NSW.