Breast cancer is the abnormal growth of cells in the breast. It usually starts in the lining of the breast ducts or lobules and can grow into cancerous (malignant) tumours.
Most breast cancers are found when they are invasive. This means that the cancer has spread into the surrounding breast tissue. Invasive breast cancer can be early, locally advanced or advanced (metastatic). Advanced breast cancer is when cancer cells have spread (metastasised) outside the breast to other parts of the body.
This information covers early and locally advanced breast cancer only.
The breasts sit on top of the upper ribs and a large chest muscle. They cover the area from the collarbone (clavicle) to the armpit (axilla) and across to the breastbone (sternum). Some breast tissue extends into the armpit and is called the axillary tail.
Female breasts are mostly made up of:
- lobes – each breast has 12–20 sections called lobes.
- lobules – each lobe contains glands that can produce milk. These milk glands are called lobules or glandular tissue.
- ducts – the lobes and lobules are connected by fine tubes called ducts. The ducts carry milk to the nipples when breastfeeding.
- fatty/fibrous tissue – all breasts contain some fatty or fibrous tissue (including connecting tissue called stroma), no matter what their size.
Most younger women have dense or thicker breasts, because they contain more lobules than fat.
Male breasts have ducts and fatty/fibrous tissue. They contain no, or only a few, lobes and lobules.
The lymphatic system
The lymphatic system is an important part of the immune system and protects against disease and infection. Working like a drainage system, it removes fluid from body tissues back into the blood.
It is made up of a network of thin tubes called lymph vessels. These lymph vessels connect to groups of small, bean-shaped lymph nodes (or glands).
There are lymph nodes throughout the body, including in the armpit, neck, abdomen, groin and near the breastbone. The first place breast cancer cells usually spread to is the axillary lymph nodes in the armpit.
Your guide to best cancer care
A lot can happen in a hurry when you’re diagnosed with cancer. The guide to best cancer care for breast cancer can help you make sense of what should happen. It will help you with what questions to ask your health professionals to make sure you receive the best care at every step.
Read the guide
Non-invasive breast conditions
These are precancerous conditions where the cells look like cancer cells but have not invaded nearby tissues and can also be called carcinoma in situ.
- Ductal carcinoma in situ (DCIS) – abnormal cells in the ducts of the breast, which may develop into invasive breast cancer. Treatment is the same as invasive breast cancer, but chemotherapy is not used.
- Lobular carcinoma in situ (LCIS) – abnormal cells in the lobules of the breast, which increases risk of developing cancer. LCIS needs regular checks through mammograms or other scans and may be treated with hormone-blocking therapy or surgery in some cases.
Invasive breast conditions
Invasive means the cancer cells have grown and spread into the surrounding tissue. The two main types of invasive breast cancer are named after the breast area that they start in.
- Invasive ductal carcinoma (IDC) – starts in the breast ducts. About 80% of breast cancers are IDC.
- Invasive lobular carcinoma (ILC) – starts in the breast lobules. About 10% of breast cancers are ILC.
Less common breast cancers include angiosarcoma, inflammatory breast cancer, medullary carcinoma, mucinous carcinoma, Paget disease of the nipple (or breast) and papillary carcinoma. Phyllodes tumour is a rare breast condition.
If invasive breast cancer spreads beyond the breast tissue and the nearby lymph nodes it is called advanced or metastatic breast cancer. For more information, call us on 13 11 20 or visit Breast Cancer Network Australia.
How common is breast cancer?
There are about 20,000 people diagnosed with breast cancer in Australia every year.
Women – breast cancer is the most common cancer in Australian women (apart from common skin cancers) – one in seven will be diagnosed in their lifetime. It is more common over the age of 40, and the risk increases with age. In rare cases, pregnant or breastfeeding women get breast cancer. See a doctor about any persistent lump noticed during pregnancy.
Men – about 160 Australian men are diagnosed with breast cancer each year — most aged over 50. It is treated in the same way as for women.
Transgender, non-binary and gender-diverse people – any transgender woman taking medicines to boost female hormones and lower male hormones has an increased risk of breast cancer (compared to a man). A transgender man, who has had breasts removed in a nipple-sparing mastectomy (usually called top surgery), can still get breast cancer – though the risk is very low. This is thought to be because small amounts of breast tissue may remain after surgery.
Learn more about breast cancer statistics and trends
Many factors can increase your risk of breast cancer, but they do not mean that you will definitely develop it. You can also have none of the known risk factors and still get breast cancer. If you are worried, speak to your doctor.
- Being female is the biggest risk factor – 99% of breast cancer cases are diagnosed in women.
- Risk increases with age for both men and women.
- About three quarters of breast cancer cases are in women over the age of 50. Free breast screening is available.
- Dense breast tissue (as seen on a mammogram) increases your risk.
- Breast implants or breast augmentation does not increase your risk of breast cancer.
- Being overweight or gaining weight after menopause. Losing weight to a healthy range can lower this.
- Drinking alcohol – the more that you drink, the higher your risk. If you choose to drink, the alcohol guidelines suggest you drink no more than 10 standard drinks a week, and no more than 4 standard drinks on any one day.
- Not getting enough exercise or not being physically active.
- Smoking tobacco may increase your risk.
- About 5–10% of breast cancers are due to an inherited breast cancer gene such as BRCA1 or BRCA2.
- Most people with breast cancer do not have a strong family history. However, having several close relatives (e.g. mother, sister, aunt) on the same side of the family who have had breast or ovarian cancer may increase your risk.
- Several close relatives on the same side of the family with prostate or pancreatic cancer may increase your risk.
- Using menopause hormone therapy (MHT) containing both oestrogen and progesterone, for long periods of time and over many years.
- Taking the pill (oral contraceptive) for a long time (small increase).
- Using some hormonal IUDs for a long time (small increase).
- You or your mother using diethylstilboestrol (DES) during pregnancy.
- Transgender women taking gender-affirming hormones for more than 5 years.
- Having been previously diagnosed with breast cancer, LCIS or DCIS.
- Some non-cancerous conditions of excessive growth of breast cells (hyperplasia).
- Having radiation therapy to the chest area for Hodgkin lymphoma.
- Males with a rare genetic syndrome called Klinefelter syndrome. Those with this syndrome have three sex chromosomes (XXY) instead of the usual two (XY).
- Never having given birth may increase risk.
- Starting your first period (menstruating) before the age of 12 may increase your risk.
- Being older than age 30 when you gave birth to your first child increases your risk.
- Not having ever breastfed may increase your risk.
- Going through menopause after the age of 55 may increase your risk.
Does breast cancer run in families?
Most people with breast cancer don’t have a family history, but a small number may have inherited a gene fault (also called a mutation or pathogenic variant) that increases their breast cancer risk.
- BRCA1 and BRCA2 – these are the most common gene mutations linked to breast cancer. Women in families with BRCA1 or BRCA2 are at increased risk of breast and ovarian cancers. Men in families with BRCA2 may be at increased risk of breast and prostate cancers.
- Other types – these include BARD1, BRIP1, NF1, RAD51C, CDH1, PTEN, STK11, TP53, PALB2, ATM and CHEK2. More gene mutations linked to breast cancer are being found all the time.
Talk to your doctor or breast cancer nurse about visiting a family cancer clinic or genetic oncologist. In particular, women diagnosed before 40, those with triple negative breast cancer, and men with breast cancer should ask for a referral.
Genetic testing is useful for people with a high chance of a gene fault, as it may help to work out the best treatment options. Medicare usually pays for testing if you have breast cancer and an increased chance of a mutation.
Not everyone who is diagnosed with breast cancer has symptoms. Breast changes may not mean cancer, but see a doctor if you have:
- a lump, lumpiness or thickening, especially in just one breast
- a change in the size or shape of the breast or swelling
- a change to the nipple – change in shape, crusting, sores or ulcers, redness, pain, a clear or bloody discharge, or a nipple that turns in (inverted) when it used to stick out
- a change in the skin – dimpling or indentation, a rash or itchiness, a scaly appearance, unusual redness or other colour changes
- swelling or discomfort in the armpit or near the collarbone
- ongoing, unusual pain not related to your monthly menstrual cycle, that remains after your period and is in one breast only.
You may be sent for tests after a screening mammogram, or your GP may arrange tests to check your symptoms. If these tests don’t rule out cancer, you will usually be referred to a specialist or breast clinic.
If breast cancer is diagnosed, you’ll see a breast surgeon or a medical oncologist, who will talk to you about your treatment options. Often these will be discussed with other health professionals at a multidisciplinary team (MDT) meeting.
During and after treatment, you will see a range of health professionals who specialise in different aspects of your care, including a breast physician, reconstructive (plastic) surgeon, breast care nurse, lymphoedema practitioner and dietician, among others.
Asking your doctor questions will help you make an informed choice. You may want to include some of these questions in your own list.
- What type of breast cancer do I have?
- Has the cancer spread? If so, where has it spread? How fast is it growing?
- Are the latest tests/treatments for this cancer available in this hospital?
- Will a multidisciplinary team be involved in my care? Will I see a breast care nurse?
- Are there clinical guidelines for this type of cancer?
- What treatment do you recommend? What is the aim of the treatment?
- Are there other treatment choices for me? If not, why not?
- If I don’t have the treatment, what should I expect?
- How long do I have to make a decision?
- I’m thinking of getting a second opinion. Can you recommend anyone?
- How long will treatment take? Will I have to stay in hospital?
- Are there any out-of-pocket expenses not covered by Medicare or my private health cover? Can the cost be reduced if I can’t afford it?
- How will we know if the treatment is working?
- Are there any clinical trials or research studies I could join?
- What are the risks and possible side effects of each treatment?
- Will I have a lot of pain? What will be done about this?
- Can I work, drive and do my normal activities while having treatment?
- Will the treatment affect my sex life and fertility?
- Should I change my diet or physical activity during or after treatment?
- Are there any complementary therapies that might help me?
- How often will I need check-ups after treatment?
- If the cancer returns, how will I know? What treatments could I have?
Expert content reviewers:
A/Prof Elisabeth Elder, Specialist Breast Surgeon, Westmead Breast Cancer Institute and The University of Sydney, NSW; Collette Butler, Clinical Nurse Consultant and McGrath Breast Care Nurse, Cancer Support Centre, Launceston, TAS; Tania Cercone, Consumer; Kate Cox, 13 11 20 Consultant, Cancer Council SA; Dr Marcus Dreosti, Radiation Oncologist and Medical Director, GenesisCare, SA; Dr Susan Fraser, Breast Physician, Cairns Hospital and Marlin Coast Surgery Cairns, QLD; Dr Hilda High, Genetic Oncologist, Sydney Cancer Genetics, NSW; Prof David W Kissane AC, Chair of Palliative Medicine Research, The University of Notre Dame Australia, and St Vincent’s Hospital Sydney, NSW; Prof Sherene Loi, Medical Oncologist, Peter MacCallum Cancer Centre, VIC; Dr W Kevin Patterson, Medical Oncologist, Adelaide Oncology and Haematology, SA; Angela Thomas, Consumer; Iwa Yeung, Physiotherapist, Princess Alexandra Hospital, QLD.
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The information on this webpage has been adapted from Understanding Breast Cancer - A guide for people with cancer, their families and friends (2022 edition). This webpage was last updated in July 2022.