Breast cancer is a relatively common type of cancer that develops in the breast, a glandular organ situated over the ribcage. While men and women both have breasts, the anatomy of the breast is slightly different between the sexes.

Breasts in females are functional organs that are used to produce milk during and after pregnancy. Female breasts are primarily made up of lobes, lobules, and ducts, which are surrounded by fatty and connective tissue. Each breast is divided into 12-20 sections called lobes.  Each lobe is made up of lobules that produce breast milk, which is then sent to the ducts. The ducts in the breasts carry milk to the nipple to be fed to babies. 

In males, the breast is a non-functional organ that cannot produce milk. Unlike female breasts, male breasts do not generally contain lobes and lobules. Ducts are present in male breasts, however they do not have a function.

Breast cancer is more common in women, and is generally diagnosed in people over 40. However, it can affect anyone with breasts – including women, teenagers, transgender men, transgender women, intersex people, non-binary individuals, children, and men – at any age. 

For information about breast cancer in men, please refer to the Rare Cancers Australia Breast Cancer (Male) page.

Types of Breast Cancer

There are several different types of breast cancer, which are classified based on the types of cells the cancer originates from.

Non-Invasive Breast Cancer

Non-invasive breast cancers, also known as carcinomas in situ, are pre-cancerous conditions that can occur in the milk ducts or the lobes of the breast. Patients with non-invasive breast cancers have cells that look like cancer cells, but they have not invaded nearby tissue. These cells may become cancerous if left untreated.

Ductal Carcinoma in Situ (DCIS)

Ductal carcinoma in situ (DCIS) is the most common type of non-invasive breast cancer, and is defined as abnormal cells in the ducts of the breasts. This condition is not cancerous, but may develop into an invasive breast cancer if left untreated. DCIS is often treated similarly to invasive breast cancers.

Lobular Carcinoma in Situ (LCIS)

Lobular carcinoma in situ (LCIS) is a less common type of non-invasive breast cancer, and is defined as abnormal cells in the lobules of the breasts. This condition is not cancerous, but may increase the risk of developing an invasive breast cancer later in life. 

Invasive Breast Cancer

Invasive breast cancers are cancerous conditions that have spread outside of the ducts and lobules, and into nearby tissue. Most breast cancers are invasive. 

Invasive breast cancers can be classified by how much they have spread. Some of these classifications include:

• Early breast cancer (cancer confined to the breast, less than 5cm, and may affect lymph nodes in the breast).
• Locally advanced breast cancer (cancer is over 5cm, or has spread to areas near the breast to the skin, chest wall and/or muscle). 
• Metastatic breast cancer (cancer that has spread to more distant parts of the body, such as the bones, liver, and/or lungs). 

Invasive breast cancers can also be classified by the type of cells they develop from.

Invasive Ductal Carcinoma 

Invasive ductal carcinoma (IDC), also known as infiltrating ductal carcinoma, is the most common type of breast cancer. It occurs when abnormal cells in the ducts of the breast have spread beyond the lining of the milk duct, and into surrounding breast tissue. While IDC can be aggressive and may metastasise, it can have a good prognosis when caught early. 

While IDC is common, there are rare subtypes of this disease, including:

• Medullary carcinoma of the breast (IDC with cells that look similar to the medulla in the brain).
• Mucinous (colloid) carcinoma of the breast (IDC that produces excess mucus (or mucin)). 
• Papillary carcinoma of the breast (IDC with cells that have finger-like projections, or papules).
• Apocrine breast cancer (IDC that have cells that appear similar to those generally found in sweat glands). 
• Tubular breast cancer (IDC that has cells that look like tubes).

Invasive Lobular Carcinoma 

Invasive lobular carcinoma (ILC) is the second most common type of breast cancer. It occurs when abnormal cells in the lobules of the breast have spread beyond the lining of the lobule, and into surrounding breast tissue. While ILC can be aggressive and may metastasise, it can have a good prognosis when caught early.

Paget’s Disease of the Nipple

Paget’s disease of the nipple, also known as Paget’s disease of the breast or mammary Paget’s disease, is a rare type of breast cancer that primarily affects the nipple and areola (area surrounding the nipple). This type of cancer is often associated with carcinomas, and often develops in people who have another form of breast cancer.

For more information on Paget’s disease of the nipple, please refer to the Rare Cancers Australia Paget’s Disease of the Nipple page.

Inflammatory Breast Cancer

Inflammatory breast cancer is a rare subtype of breast cancer that develops from the blood vessels in the skin of the breast and/or the lymphatic vessels of the breast. It generally occurs when cancer cells block these vessels, causing the breast to become swollen and red. Inflammatory breast cancer is generally aggressive, likely to metastasise, and may not have as good of a prognosis as other types of breast cancer.

Phyllodes Tumours in the Breast

Phyllodes tumours in the breast are a very rare subtype of breast cancer that begins in the connective or stromal tissue in the breast (outside of the ducts, lobules and lobes). Most of these cancers are benign, however in rare cases they may be malignant. Malignant phyllodes tumours of the breast can be aggressive, rarely metastasise, and can have a good prognosis when caught early.

Metaplastic Breast Cancer

Metaplastic breast cancer is a very rare subtype of breast cancer that may contain different types of cancer cells. It begins in the ducts of the breast, and contains cells that look like IDC. However, in addition to these cells, the cancer may also contain cells resembling soft tissue and connective tissue in the breast. While it is not known how this occurs, it is thought that ductal cells undergo a change in form (or metaplasia) to become different cells. Metaplastic breast cancer is generally aggressive, likely to metastasise, and may not have as good of a prognosis as other types of breast cancer.

Angiosarcoma of the Breast

Angiosarcomas of the breast are a very rare subtype of breast cancer that develop in the lining of blood vessels or lymph vessels in the breast. This type of cancer is often more aggressive than other types of breast cancer.

For more information on angiosarcoma of the breast, please refer to the Rare Cancers Australia Angiosarcoma page.

Pregnancy-Associated Breast Cancer

Pregnancy-associated breast cancer (PABC), also known as pregnancy-related breast cancer or gestational breast cancer, is a very rare type of breast cancer that is diagnosed in women during pregnancy, or in the first year after the baby has been born. In most cases, PACB occurs as an IDC, but can also occur as other types. This type of cancer is often diagnosed late due to the changes of the body throughout pregnancy and/or breastfeeding. PACB is often aggressive, likely to metastasise, and may not have as good of a prognosis as other types of breast cancer.

Breast Cancer Receptor Status

In addition to the types of cells they originate from, breast cancers are also classified by their receptor status. 

Receptors are defined as proteins on the surface of the cells that signal a specific response in the body. These cells can initiate many important functions within a cell, such as cell growth, cell division, or cell death. Cancer cells have unique receptors that promote their growth and survival.

In breast cancer, there are three main types of receptors that cancer cells are tested for.

Hormone Receptors

When breast cancers have hormone receptors on them (or are hormone receptor positive), the growth of the cancer cells are influenced by the female hormones’ oestrogen and progesterone. The cancer cells can have oestrogen receptors (OR), progesterone receptors (PR), or a combination of both. Many cancers are hormone receptor positive, and are often treated hormone-blocking therapy. 

Human Epidermal Growth Factor Receptor 2 (HER2)

Human epidermal growth factor receptor 2 (HER2) is a receptor on the surface of normal cells that help maintain cell growth. In HER2 positive cancer cells, there is excess HER2 which promotes the growth of cancer cells. HER2 breast cancers are generally hormone receptor negative, but can be positive in rare instances. Breast cancers that are positive for this receptor generally grow faster than those without it. 

Triple Negative Breast Cancer

Triple negative breast cancer occurs when breast cancer cells are negative for both hormone receptors (oestrogen and progesterone receptors) and HER2. This type of cancer is rare, grows quickly, and is often aggressive. 

Treatment 

If breast cancer is detected, it will be staged and graded based on size, metastasis (whether the cancer has spread to other parts of the body) and how the cancer cells look under the microscope. Staging and grading helps your doctors determine the best treatment for you. 

Cancers can be staged using the TNM staging system: 

• T (tumour) indicates the size and depth of the tumour. 
• N (nodes) indicates whether the cancer has spread to nearby lymph nodes. 
• M (metastasis) indicates whether the cancer has spread to other parts of the body. 

This system can also be used in combination with a numerical value, from stage 0-IV: 

• Stage 0: this stage describes cancer cells in the place of origin (or ‘in situ’) that have not spread to nearby tissue. 
• Stage I: cancer cells have begun to spread to nearby tissue. It is not deeply embedded into nearby tissue and had not spread to lymph nodes. This stage is also known as early-stage cancer.
• Stage II: cancer cells have grown deeper into nearby tissue. Lymph nodes may or may not be affected. This is also known as localised cancer. 
• Stage III: the cancer has become larger and has grown deeper into nearby tissue. Lymph nodes are generally affected at this stage. This is also known as localised cancer. 
• Stage IV: the cancer has spread to other tissues and organs in the body. This is also known as advanced or metastatic cancer.

Cancers can also be graded based on the rate of growth and how likely they are to spread: 

• Grade I: cancer cells present as slightly abnormal and are usually slow growing. This is also known as a low-grade tumour. 
• Grade II: cancer cells present as abnormal and grow faster than grade-I tumours. This is also known as an intermediate-grade tumour.  
• Grade III: cancer cells present as very abnormal and grow quickly. This is also known as a high-grade tumour.  

Once your tumour has been staged and graded, your doctor may recommend genetic testing, which analyses your tumour DNA and can help determine which treatment has the greatest chance of success. They will then discuss the most appropriate treatment option for you.  

Treatment for breast cancers may include:

• Surgery, potentially including:
  • Breast-conserving surgery/Lumpectomy (removal of the tumour and a healthy margin of tissue around it).
  • Unilateral mastectomy (complete removal of one breast).
  • Bilateral mastectomy (complete removal of both breasts). 
  • Breast reconstruction (usually performed after a mastectomy to make a new breast shape). 
  • Lymphadenectomy (removal of affected lymph nodes). 
• Chemotherapy.
• Radiation therapy. 
• Hormone-blocking therapy (for hormone receptor positive cancers), potentially including:
  • Tamoxifen.
  • Aromatase inhibitors.
  • Ovarian suppression. 
• Targeted therapy (commonly for HER2 positive cancers), including:
  • Trastuzumab.
  • PARP (poly adenosine diphosphate ribose polymerase) inhibitors.
  • Herceptin.
  • Perjeta.
  • Kadcyla.
  • Tykerb.
• Clinical trials.
• Palliative care.

For more information on the treatment options, please refer to the Rare Cancers Australia treatment options page.  

Breastfeeding and Breast Cancer Treatment

Treatment for breast cancer may affect your ability to breastfeed. If this is a concern to you, discuss your options with your doctor prior to the commencement of treatment.

Risk factors 

While the cause of breast cancer remains unknown, the following factors may increase the likelihood of developing the disease:

• Being female. 
• Being over 40 years old.
• Being overweight/obesity.
• Alcohol consumption.
• Not getting enough exercise. 
• Having a history of smoking. 
• Having specific genetic mutations, most commonly associated with the BRCA1 and BRCA2 genes.
• Certain hormonal therapies, potentially including:
  • Menopause hormonal therapy (MHT). 
  • Hormone replacement therapy (HRT).
  • Oral contraceptive over long periods of time. 
  • Hormonal intrauterine devices (IUDs) over long periods of time. 
  • Diethylstilboestrol (DES) when your mother or you were pregnant.
  • Gender-affirming hormones for more than five years.
• Having a family history of breast cancer, DCIS, and/or LCIS.
• Hyperplasia of breast cells. 
• Previous radiation therapy to the chest area for Hodgkin lymphoma.
• Klinefelter syndrome.
• Li-Fraumeni syndrome. 
• Reproductive factors, potentially including:
  • Never having given birth.
  • Beginning menstruation before the age of 12.
  • Being over 30 when you gave birth to your first child.
  • Never having breastfed.
  • Going through menopause over the age of 55.
• Having a personal history of cancer.

Not everyone with these risk factors will develop the disease, and some people who have the disease may have none of these risk factors. See your general practitioner (GP) if you are concerned.

Early symptoms 

In the early stages of breast cancer, the disease may be asymptomatic. As the cancer progresses, some of the following symptoms may appear:

• A lump or lumpiness in the breast(s).
• A change in the size and/or shape of the breast.
• Swollen breasts. 
• Changes to the nipple, potentially including:
  • Changes in shape.
  • Crusting, sores and/or ulcers.
  • Unusual redness.
  • Pain.
  • Clear or bloody discharge.
  • Inverted nipple (nipple turns inward when it used to face outward).
• Dimpling or indentation on the skin of the breast.
• A rash and/or itchiness of the breast.
• A scaly appearance and/or changes in the colour of the breast.
• Swelling or discomfort in the armpit or near the collarbone.
• Persistent, unusual pain not associated with the menstrual cycle.

Not everyone with the symptoms above will have cancer, but see your GP if you are concerned. 

Diagnosis/diagnosing 

If your doctor suspects you have breast cancer, they may order the following tests to confirm the diagnosis and refer you to a specialist for treatment. 

Physical examination 

Your doctor will collect your overall medical history, as well as your current symptoms. Following this, they will examine your body (more specifically, around breasts) to check for any abnormalities. 

Imaging & blood tests 

The doctor will take images of your body using magnetic resonance imaging (MRI), a computed tomography scan (CT scan), mammogram, tomosynthesis/DBT, and/or positron emission tomography (PET scan), depending on where it is suspected the cancer is. The doctor may also look at other parts of the body and looks for signs of metastasis. Additionally, a blood test may be taken to assess your overall health and help guide treatment decisions. 

Biopsy

A biopsy is a procedure that is undertaken to remove a sample of tissue or cells from the body to be tested in a laboratory to detect any abnormalities. The tissue sample will then be analysed for cancer cells. This can be done by a fine needle aspiration (FNA), a core needle biopsy (CNB), a vacuum-assisted core biopsy, or a surgical biopsy.  

Prognosis (Certain factors affect the prognosis and treatment options) 

While it is not possible to predict the exact course of the disease, your doctor may be able to give you a general idea based on the rate and depth of tumour growth, susceptibility to treatment, age, overall fitness, and medical history. Generally, early-stage breast cancers have a better prognosis and survival rates. However, if the cancer is advanced and has spread, the prognosis may not be as good and there may be a higher risk of cancer recurrence. It is very important to discuss your individual circumstances with your doctor to better understand your prognosis.   

References 

• Breast Cancer Network Australia
• Cancer Australia
• Cancer Council
• Johns Hopkins Medicine

^{Some references are to overseas websites. There may be references to drugs and clinical trials that are not available here in Australia.}