Understanding Breast Cancer
Breast cancer is the most commonly diagnosed cancer in women worldwide and remains one of the leading causes of cancer-related death. In Australia, it is estimated that around 21,000 people are diagnosed with breast cancer each year, with approximately 1 in 7 women and 1 in 550 men developing breast cancer during their lifetime. While a breast cancer diagnosis can be overwhelming, advances in screening, diagnosis and treatment have resulted in significantly improved survival rates, with many people living long and healthy lives after treatment.
Breast cancer is not a single disease. There are many different types and subtypes of breast cancer, each with unique characteristics that influence how the cancer behaves, how quickly it grows and which treatments are likely to be most effective. Understanding these differences can help individuals better understand their diagnosis and feel more informed throughout their treatment journey.
What is Breast Cancer?
Breast cancer develops when cells within the breast tissue begin to grow abnormally and uncontrollably. Normally, cells grow, divide and die in an organised way. Cancer develops when genetic mutations cause cells to continue dividing when they should not. These abnormal cells can form a tumour (an abnormal mass of tissue) that can remain localised, invade surrounding tissues or spread to other parts of the body.
Most breast cancers begin in one of two areas of the breast:
- The milk ducts, which carry milk to the nipple (known as ductal cancers)
- The milk-producing lobules, where breast milk is produced (known as lobular cancers)
The breast is made up of glandular tissue, fatty tissue, connective tissue, blood vessels and a network of lymphatic vessels that drain fluid towards nearby lymph nodes. The lymph nodes in the armpit (axilla) are particularly important in breast cancer, as cancer cells can travel through the lymphatic system to these nodes before potentially spreading to other parts of the body.
Signs and Symptoms of Breast Cancer
Many breast cancers are detected through routine screening before symptoms develop. However, it is important to be familiar with what is normal for your breasts and seek medical assessment if any changes occur.
Possible signs and symptoms include:
- A new lump or thickening in the breast or armpit
- A change in the size or shape of the breast
- Skin dimpling or puckering
- Redness or swelling of the breast
- Thickened skin with an ‘orange peel’ appearance (peau d’orange)
- A nipple that becomes inverted or changes position
- Nipple discharge, particularly if bloody or occurring without squeezing
- Persistent breast or nipple pain
- A rash, ulceration or crusting around the nipple
- Swollen lymph nodes in the armpit or above the collarbone
It is important to remember that most breast changes are not caused by breast cancer. Benign breast conditions are common, but any persistent or concerning change should be assessed by a healthcare professional.
Risk Factors for Breast Cancer
Breast cancer develops due to a combination of genetic, hormonal, environmental and lifestyle factors. Having one or more risk factors does not mean someone will develop breast cancer, and many people diagnosed with breast cancer have no obvious risk factors.
Known risk factors include:
Increasing age: Age is the strongest risk factor for breast cancer, with most diagnoses occurring in people over the age of 50.
Female sex: Women have a much higher risk of developing breast cancer than men due to differences in breast tissue and lifetime hormone exposure.
Family history and inherited gene mutations: Most breast cancers occur in people with no family history. However, approximately 5–10% are associated with inherited gene mutations such as BRCA1, BRCA2, PALB2, CHEK2 and several other less common genes. People with a strong family history of breast or ovarian cancer may benefit from referral to a familial cancer clinic or genetic counselling service.
Hormonal factors: Factors associated with prolonged exposure to oestrogen slightly increase breast cancer risk, including:
- Early onset of menstruation
- Late menopause
- Having no children
- Having a first pregnancy later in life
- Some forms of hormone replacement therapy
Breast density: Having dense breast tissue is associated with an increased risk of developing breast cancer. Dense breasts contain a greater proportion of glandular and connective tissue relative to fatty tissue.
Previous radiation exposure: Radiation therapy to the chest during childhood or early adulthood, particularly for conditions such as lymphoma, increases future breast cancer risk.
Lifestyle factors: Several lifestyle factors have been linked to an increased risk of breast cancer, including:
- Alcohol consumption
- Physical inactivity
- Overweight and obesity, particularly after menopause
- Smoking
Regular physical activity, maintaining a healthy weight and limiting alcohol intake may help reduce risk.
How is Breast Cancer Diagnosed?
If breast cancer is suspected, several investigations may be performed to confirm the diagnosis and determine the extent of disease.
Clinical Breast Examination
A doctor will examine both breasts and nearby lymph nodes, assessing for lumps, skin changes or enlarged lymph nodes.
Mammography
Mammography is the primary imaging test used to detect breast cancer and is the foundation of Australia’s BreastScreen program. Mammograms can identify very small cancers before they become noticeable and often detect abnormalities such as microcalcifications associated with DCIS.
Breast Ultrasound
Ultrasound is commonly performed alongside mammography, particularly in younger people or those with dense breast tissue. It helps distinguish solid masses from fluid-filled cysts and provides additional information about suspicious abnormalities.
Breast MRI
Magnetic Resonance Imaging (MRI) is not routinely required for everyone but may be recommended in selected situations, including for:
- Dense breast tissue
- Lobular breast cancer
- High genetic risk
- Assessing the extent of disease
- Monitoring response to chemotherapy before surgery
Breast Biopsy
A biopsy is the only way to definitively diagnose breast cancer. Using imaging guidance, a small sample of tissue is removed with a needle and examined under a microscope by a pathologist. The biopsy identifies:
- The type of breast cancer
- Tumour grade
- Hormone receptor status
- HER2 status
- Other biological features
These results form the basis of treatment planning.
What Comes Next?
Receiving a breast cancer diagnosis often introduces a whole new vocabulary, with terms like ductal carcinoma, lobular carcinoma, HER2-positive, triple negative, grade and stage becoming part of conversations with your healthcare team. It’s completely normal to feel overwhelmed by this information, and many people tell us they don’t fully understand what these terms mean or even remember the specific details of their diagnosis.
In Part 2 of this series, we’ll explain the different types and subtypes of breast cancer, the difference between non-invasive and invasive disease, what staging and grading mean, and how to interpret the key information found in a pathology report. Understanding these terms can help you feel more informed about your diagnosis, the treatments recommended by your medical team, and the rehabilitation journey that follows.
References
Australian Institute of Health and Welfare. (2024). Breast cancer. Australian Government. https://www.aihw.gov.au/reports/cancer-screening/breast-cancer-in-australia
Cancer Australia. (2024). Breast cancer statistics. Australian Government. https://www.canceraustralia.gov.au/cancer-types/breast-cancer/statistics
Cancer Council Australia. (2026). Breast cancer: Symptoms, risks and screening. https://www.cancer.org.au/types-of-cancer/breast-cancer/symptoms-risks-and-screening
Cancer Council Australia. (2026). Breast cancer. https://www.cancer.org.au/types-of-cancer/breast-cancer
Healthdirect Australia. (2026). Breast cancer. Australian Government. https://www.healthdirect.gov.au/breast-cancer
National Breast Cancer Foundation. (2025). Breast cancer: Understanding the disease. https://nbcf.org.au/about-breast-cancer/
National Comprehensive Cancer Network. (2025). NCCN Guidelines for Patients: Breast Cancer. https://www.nccn.org/patients
Disclaimer
This content is general in nature and provided for educational purposes only. It is not a substitute for individualised medical advice, diagnosis, or treatment. If you have concerns about your symptoms or health, consult a qualified healthcare professional.
