The Facts

A woman's breast is made up of milk glands and milk ducts, surrounded by fatty tissue and connective supports. Uncontrolled growth of cells in any of these breast tissues can cause breast cancer.

Breast cancer is the most common cancer among women. It tends to occur at an earlier age than do other cancers or heart attacks and strokes. Chances of developing breast cancer rise dramatically as women age: 13 out of 1,000 women in their 40s; 23 out of 1,000 women in their 50s; 29 out of 1,000 women in their 60s; 31 out of 1,000 women in their 70s.

Breast cancer is rare in men, accounting for less than 1% of all cases. Breast cancer is the second most common cause of death from cancer in women.


The body's cells reproduce themselves throughout your lifetime, as tissues wear out and their cells are replaced in a controlled manner. Breast cancer - like all cancers - occurs when that control is lost and cells begin to divide at an unusually high rate.

No single trigger or cause has been identified for breast cancer. Certain risk factors exist, though, that increase a woman's chance of developing it:

  • age - it's more common in women over 50
  • family history - if a woman's mother or sister had the disease before menopause, this is occasionally associated with one of two genes linked to breast cancer
  • previous breast cancer
  • family history of ovarian cancer
  • age of pregnancy - women who haven't had children, or whose first child was born after age 30
  • age of menstruation - starting periods at a young age (under 12 years old)
  • entering menopause later (over age 55) increases breast cancer risks
  • recent research suggests that women who start smoking regularly within 5 years of the onset of their menstrual periods are 70% more likely to develop breast cancer before the age of 50 than non-smokers
  • having dense breast tissue
  • radiation treatment to the chest, especially before 30 years of age
  • alcohol consumption contributes to the risk of breast cancer
  • hormone replacement therapy (HRT; estrogen plus progesterone) increases the risk of breast cancer slightly after 5 years of therapy
  • oral contraceptives increase risks slightly, if used over many years
  • obesity with excess caloric and fat intake

The increased risks of getting breast cancer associated with the above factors are often statistically quite small. In fact, for most women, the only risk factor they have is being over 50 years of age. Any concerns should be discussed with your doctor.

Symptoms and Complications

9 out of 10 times, women are the first to notice a lump or mass in their breast. It usually isn't painful, but can cause an unusual sensation in the area where the lump is.

When a tumour grows in the milk ducts, bleeding can occur from the nipple. The size or shape of the breast may change. As well, the nipple might draw in, or some of the skin will pull in, causing what looks like a dimple to appear. Other symptoms may include a lump or swelling in the armpit and redness or swelling of the breast.

While these might be signs of breast cancer, they might also indicate another non-cancerous condition. In fact, about 8 out of 10 breast growths are non-cancerous. However, a doctor should be consulted to determine the exact cause of the lump.

The most serious complication of breast cancer is metastasis. That's when some cells from a tumour break off and move to other areas of the body, either through the blood or the lymphatic vessels - invading the tissue at new, possibly distant sites. When breast cancer cells metastasize, it's most commonly to the lymph nodes, lungs, liver, bones, brain, and skin. It can take years, even after the breast tumour is diagnosed and treated, before cancer that has spread from the original tumour appears.

Once metastatic tumours are discovered, chances are that the cancer has spread to other locations as well, even if they remain undetected.

Making the Diagnosis

A suspicious lump in your breast should be checked by your doctor. Aside from an extensive physical examination, the doctor will also want to do a mammogram, which is a low-level X-ray that can show abnormal areas in your breast. An ultrasound can sometimes be performed to see if the lump is a fluid-filled cyst or a solid growth. Even if the lump that can be felt is not visible on the mammogram, some sort of biopsy may need to be done.

Using a needle, fluid can be removed from a cyst to check if it contains cancerous cells. A solid lump must be analyzed under a microscope. This requires either a needle biopsy, a core biopsy, or a surgical biopsy to be performed.

For a needle biopsy, a fine needle is inserted into the lump and cells are drawn out with the needle. With a core biopsy, a sample of breast cells and tissues is removed for examination. A surgical biopsy is an operation that removes the whole lump and some normal tissue around it. It can be done under a local or general anesthetic.

Cancerous cells can be tested for the presence of estrogen or progesterone receptors. Other tests, including X-rays, bone scans, ultrasounds, CT scans, or an MRI, may be done to see if the cancer has spread to other organs and tissues.

Treatment and Prevention

Early detection of breast cancer minimizes the likelihood that the cancer has spread, and it increases the chances of making a complete recovery.

Treatment depends on individual circumstances, such as the rate of growth, how it responds to treatment, and whether or not it has spread. Treatment options for breast cancer include surgery, radiation therapy, chemotherapy, and medication therapy (including hormone and biological therapy).

With surgery, part or all of the breast is removed. Removal of a small part of the breast (only the tumour and some surrounding tissue) is called a lumpectomy, or partial mastectomy if a larger area of the breast is removed. A simple mastectomy involves removing the whole breast, and a radical mastectomy includes the underlying chest muscle and tissue as well. The lymph nodes in the underarms may also be taken out. Breast reconstruction surgery may be an option for many women either at the time of surgery or at a later date.

Chemotherapy is usually given by injection. Chemotherapy interferes with the growth of cancer cells, but it also affects healthy cells. Common side effects of chemotherapy can include nausea, vomiting, hair loss, and infection.

Hormonal therapy (e.g., tamoxifen*) also helps stop the growth of cancer cells and may be used for up to 5 years for postmenopausal women who have receptor-positive cancer. Common side effects of hormonal therapy include hot flashes and irregular menstruation.

On rare occasions, systemic therapy is used prior to surgery. This is called neoadjuvant therapy. This type of treatment is used to improve chances of recovery, to allow surgery to take place successfully, and to assess the response of the tumour to systemic therapy (which cannot occur if the tumour is already removed).

Radiation therapy is often administered after lumpectomy or partial mastectomy. Radiation kills cancer cells in the breast and sometimes in the armpit and chest wall as well. Side effects of radiation therapy such as skin redness and tiredness are the result of healthy tissue in the area being destroyed, and go away on their own following the completion of therapy.

While successful surgery and radiation therapy rely on exact knowledge of where the tumour is located, systemic therapy does not. Chemotherapy involves taking one or more medications to destroy cancer cells in various parts of the body. Hormone therapy works on cancerous cells that have estrogen receptors, making them susceptible to estrogen-blocking medications. The source of the hormones that stimulate growth - ovaries or the adrenal gland - may also be surgically removed.

Biological therapy interferes with the growth of cancer cells and helps the body to kill cancer cells. It is usually used for breast cancer that has too much of a protein called HER2. Biological therapy is given by injection and is associated with side effects such as fever, chills, and headache.

For some women with a high risk of breast cancer, research has shown that an anti-estrogen medication may be used to help prevent breast cancer.

Since there are risks associated with any medication, the decision to use preventative therapy should be made after knowing all of the risks and benefits of treatment.

There are also other steps you can take to reduce your risk of breast cancer:

  • exercise regularly
  • eat a healthy, low-fat diet with lots of fruits and vegetables
  • reduce alcohol intake (risk increases with the amount of alcohol consumed; even 1 to 2 drinks per day can slightly increase your risk)
  • consider the risks of taking hormone replacement therapy (especially for more than 5 years)
  • avoid smoking

In addition, women should become familiar with the usual look and feel of their breasts. This will ensure you are aware of any changes in your breasts. Report any changes to your doctor.

From age 50 to 69, women of average risk should also have mammograms every 2 years. If you have a higher than average risk of breast cancer or are outside of this age range, ask your doctor when you should have a mammogram. These measures help detect any unusual lumps or abnormalities in breast tissue. Early detection can make a big difference in successful treatment.


*All medications have both common (generic) and brand names. The brand name is what a specific manufacturer calls the product (e.g., Tylenol®). The common name is the medical name for the medication (e.g., acetaminophen). A medication may have many brand names, but only one common name. This article lists medications by their common names. For information on a given medication, check our Drug Information database. For more information on brand names, speak with your doctor or pharmacist.