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Breast Cancer

Breast cancer starts in the cells that line the ducts or the lobule of the breast.“Diagram of the female breast with a cancerous tumour”

There are 2 ways to describe breast cancer:

  • Invasive breast cancers extend beyond the wall of the milk duct and into the surrounding tissues.
  • Non-invasive breast cancers do not extend beyond the wall of the milk duct into the surrounding breast tissues.

To learn more about breast cancer, visit the Canadian Cancer Society.

What’s on this Page

You will find Cancer Care Ontario information, resources and tools for:

  • patients, families and caregivers 
  • anyone interested in breast cancer 
  • healthcare providers

You will also find links to other organizations that provide information related to breast cancer.


There are several things that can lower your risk of breast cancer:

Limit the Amount of Alcohol You Drink

For breast cancer, there is no safe limit for drinking alcohol. Even drinking small amounts of alcohol can raise your risk. Compared with no drinks a day, each daily alcoholic drink raises your risk of getting breast cancer by almost 10%. 

Maintain a Healthy Weight

If you are not at a healthy weight, losing even a small amount of weight can help lower the risk to your health. Small changes in your diet and physical activity may be enough to help you become healthier.

Stay Active

Being physically active can improve your health, well-being and quality of life, and lower your risk of cancer.

Being “active” does not mean just formal exercise programs — lots of everyday activities, such as gardening, housework, walking to work or the store, or dancing, also count. Being active may also help you to reach and keep a healthy weight.

Talk to Your Doctor About the Benefits and Risks of Birth Control Pills and Hormone Replacement Therapy

If you have taken birth control pills, you may have a higher risk of breast cancer than a woman who has never taken them. When you stop taking birth control pills, your risk of breast cancer starts to go down.

Hormone replacement therapy (HRT) may be used to treat the symptoms of menopause, like hot flashes. Taking HRT may raise your risk of breast cancer, especially if you take the type that contains both estrogen and progesterone for a long time. Your risk quickly falls after you stop taking HRT.

Be sure to speak with your doctor or nurse practitioner before making any medication changes.

Learn About the Effects of Pregnancy and Breastfeeding

Being pregnant and giving birth, especially earlier in life, may lower your risk of getting breast cancer. Breastfeeding, particularly for 1 year or more over the course of a lifetime, may also lower your breast cancer risk.

Check If You Are High Risk

The genes you are born with and whether your family members have had cancer also play a part in your risk of getting cancer. Some women have gene mutations that run in their family and increase their risk for breast cancer (e.g., BRCA1, BRCA2, TP53, PTEN, CDH1). Most women diagnosed with breast cancer do not have a significant family history of the disease.

Genetic testing may tell if you have genetic changes (mutations) that increase the risk of certain cancers, like breast cancer. Genetic testing may be right for you if any of the following are true: 

  • You have a personal or family history of breast or ovarian cancer
  • You are diagnosed with breast cancer before age 35
  • You have a strong family history of breast, ovarian or related cancers. The more relatives you have with a history of cancer and the younger they were when diagnosed, the higher your chances are of having a genetic mutation
  • You are a first-degree relative (parent, brother, sister or child) of someone who has a gene mutation that increases their risk for breast cancer (e.g., BRCA1, BRCA2, TP53, PTEN, CDH1)
  • You have a family history of male breast cancer
  • You are of Ashkenazi Jewish descent

Women who meet the referral criteria on the OBSP Requisition for High Risk Screening are referred to the High Risk Ontario Breast Screening Program (High Risk OBSP) by their doctor. To find out if you are eligible, you may be referred to a High Risk OBSP site or a genetics clinic, which will do a genetic assessment and, if appropriate, genetic testing.

Talk to your doctor to see if you would benefit from genetic assessment. 

For more screening information, visit the Ministry of Health and Long-Term Care's breast cancer screening services

For more details on genetic testing, visit the Canadian Cancer Society.


Cancer screening is testing done on people who may be at risk of getting cancer, but who have no symptoms and generally feel fine.

Regular breast cancer screening is important because it can find cancer early when it may be smaller and easier to treat. Screening mammography can find breast cancers when they are small, less likely to have spread, and more likely to be treated successfully.

Who Should Get Screened

If you are age 50 to 74, the Ontario Breast Screening Program (OBSP) recommends that most women in your age group get screened every 2 years with mammography. Find your nearest OBSP site by calling 1-800-668-9304 or visiting Ontario Breast Screening Program locations.

If you are age 30 to 69 and think you may be at high risk of getting breast cancer, speak with your doctor about being referred to the High Risk OBSP. You can get screened through the High Risk OBSP if you meet certain criteria. See Breast Cancer Screening for Women at High Risk for more information.

To find out when and where to get screened, and learn about mammograms, the Ontario Breast Screening Program and more, go to the Screening for Breast Cancer page.


During diagnosis, a person may need many tests to confirm the cancer. Waiting for test results to come back can be stressful. If you are waiting for a diagnosis, talk to your doctor or nurse practitioner about managing stress during this difficult time.

For information about diagnostic tests for breast cancer, visit the Canadian Cancer Society.

Starting the Diagnostic Process

Not every patient follows the same diagnostic process. Some people may be helped through the process by their family doctor, while others may be helped by a specialist, the Ontario Breast Screening Program or a Diagnostic Assessment Program (DAP).

In many cases, a family doctor is the first contact in the process of diagnosing cancer, and is the one to refer a patient to a specialist or Diagnostic Assessment Program.


Treatment for breast cancer will depend on:

  • the type of cancer 
  • the stage of cancer
  • which treatments the person chooses to have 

Treatments may include:

  • surgery
  • drug therapy (chemotherapy) 
  • radiation therapy
  • other treatment options
  • clinical drug trials

To learn more about types of breast cancer treatment, visit the Canadian Cancer Society.

Drug Therapy Information

You can learn more about specific cancer drugs using our patient information sheets. These provide information about cancer drug therapies, including what they are used for and how to manage side effects. To find patient information sheets, go to the Drugs page.

You can also see About Chemotherapy for general information about cancer drug therapy.

Quitting Smoking Can Help Your Treatment

It’s never too late to quit smoking. Whether you are scheduled to have surgery, radiation treatment or chemotherapy, quitting smoking can help your treatment work better. It also can reduce the chance of your cancer coming back or getting another form of cancer. For more information and resources, see Benefits of Quitting Smoking for People with Cancer.

Managing Symptoms and Side Effects

People with cancer may have symptoms related to their cancer or as a side effect of treatment. 

Our symptom management guides explain:

  • how to recognize symptoms
  • what to do and what not to do 
  • when to contact your healthcare team

The guides are available for patients and for healthcare providers. Each patient guide also comes with links to helpful resources like courses, books, videos and worksheets.

Our side effect information sheets offer tips for people who have side effects from chemotherapy treatment.

If you are a person with cancer, please remember that it’s important to discuss any symptoms or concerns with your healthcare team.

Clinical Trials

Clinical trials are scientific studies that test the safety and effectiveness of a medical treatment. Find clinical trials in Canada.

Palliative Care

Palliative care supports people with life-threatening illness and their families. The goal of this care is to relieve suffering so people can have the best possible quality of life. Palliative care should start when a person is diagnosed with a serious illness.

To learn more, go to the Palliative Care page.

After Treatment

When treatment ends, a person moves into a new phase of their cancer experience. For many patients, a lot of the after-treatment care will be given by healthcare providers in the community, like a family doctor or nurse practitioner.

Follow-Up Care

Follow-up care is the care given after active treatment for breast cancer is over. It focuses on:

  • helping the person recover from the cancer and treatments
  • finding cancer early if it comes back

Follow-up care can also involve Breast Reconstruction Surgery.

To learn more about follow-up care, visit the Canadian Cancer Society.

Managing Ongoing Symptoms

A person may have symptoms from cancer for months or years after treatment has ended. These are called long-term effects or late effects.

If you have ongoing symptoms after being treated for cancer, you can find information on how to manage them in our Symptom and Side Effect Management guides.

To better understand the late or long-term effects of cancer treatment, visit the Canadian Cancer Society for a helpful overview.

End-of-Life Care

Each person has a different experience during their final months and days of life. Their symptoms may change as their illness continues, and their needs for information and support will be unique. Family members will also have questions, concerns and needs of their own.

If you are helping a family member through their final months of life, talk to your healthcare team about your questions and concerns as they come up. They can give you information and resources to support you and your family, and help you make decisions and plan for end-of-life care.

For more information, go to the Palliative Care page.


  • Breast cancer was expected to be the most common cancer diagnosed in Ontario women in 2018.
  • One in 8 Ontario women is expected to be diagnosed with breast cancer in their lifetime. Breast cancer has one of the highest survival rates in Ontario. 
  • Breast cancer risk increases with age.
  • In Ontario, breast cancer occurs mostly in women ages 50 to 74 (61% of cases).
  • It was estimated that about 11,762 Ontario women  would be diagnosed with breast cancer and about 1,977 women  would die from the disease in 2018.
  • Less than 1% of women in the general population are estimated to be at high risk for breast cancer.
  • Women at high risk have a greater estimated lifetime risk of getting  breast cancer (up to 85%) than the general population (10% to 12%).
  • Women at high risk can get breast cancer at an earlier age and their breast cancers tend to be more aggressive than those diagnosed in most women.