Breast cancer facts & risk factors

How common is breast cancer?

Breast cancer is the cancer diagnosed most frequently in North American women. Nearly 200,000 new cases are diagnosed in American and Canadian women each year and nearly 65,000 women die from the disease each year in the USA and Canada.

What is my risk of developing breast cancer?

One statistic that is often quoted is that women have a 1 in 9, or even a 1 in 8 chance of developing breast cancer. This number is alarming and needs explanation. It is true that a woman has a 1 in 9 (or 11%) chance of developing breast cancer, but this is true only if she lives to the age of 90. Many women do not live to this age. A more useful way of assessing your risk for developing breast cancer is to know your risk over the next year, or the next 5 years or up to a certain age.

The chance of developing breast cancer increases with age. Therefore, your age at the present time very much determines your risk of breast cancer over the next year or 5 to 10 years.

Number of women per year at risk of developing breast cancer
Age Risk
30 1 in 6,000
40 1 in 1,200
50 1 in 550
60 1 in 400
70 1 in 300
80 1 in 250
Average woman's risk of developing breast cancer
Age Risk
25 under 1 in 1,000
50 1 in 63
75 1 in 15
90 1 in 9


Other risk factors, besides age, that add to the risk of developing breast cancer include the following:

Strong risk (greater than 4 times normal)

  • female sex
  • advancing age
  • previous cancer in one breast (especially lobular carcinoma)
  • family history of breast cancer: pre-menopausal or in both breasts
  • past breast biopsy showing severely abnormal cells and hyperplasia

Moderate risk (2 to 4 times normal)

  • over 30 years old at birth of first child
  • past breast biopsy: any sign of cell abnormality or hyperplasia
  • post-menopausal obesity
  • diet (possibly)

Weak risk (up to 2 twice normal)

  • first menses before the age of 12 years
  • menopause after the age of 54 years
  • family history of breast cancer: older post-menopausal
  • prolonged hormone use (more than 15 years)
  • moderate to heavy alcohol consumption

Risk factors that increase your chances of developing breast cancer:

Family history

A single case of breast cancer among close relatives (mother, sisters, daughters, grandmothers and aunts) only increases your personal risk a small amount, especially if the cancer was diagnosed when your relative was over 50 years old. However, the risk of a hereditary predisposition to cancer is higher if there are several cases of breast cancer in your family. This is especially true if any cases were diagnosed before age 50, or if anyone had cancer in both breasts.

Your menstrual and reproductive history

Prolonged exposure to estrogen increases your chance of developing breast cancer. Estrogen stimulates the cells in the breasts' milk ducts, from which cancers develop. The risk of breast cancer is increased:

  • if your periods started early (before age 12) and ended late (after age 56).
  • if you have not been pregnant. However, an early first full term pregnancy (before age 20) seems to have a protective effect on the cells in the milk ducts and such women have a lower than average risk of breast cancer.
  • if you have used estrogen after menopause for a long time, more than 5 to 10 years. This weakly increases the chance of breast cancer.

Previous breast biopsies

Most benign or fibrocystic changes seen in a breast biopsy are not indicators of future cancer. However, if the cells in the normal milk ducts are beginning to look abnormal (called atypia) or heap up in an abnormal number (called hyperplasia), the risk of developing breast cancer later is increased by a modest amount.


The North American lifestyle results in higher rates of breast cancer than the lifestyles in Africa or Asia. This may be due to differences in menstrual and reproductive patterns, but affluence and diet are also likely important.


Regularly drinking more than 2 alcoholic drinks a day and obesity after menopause have been linked to higher rates of breast cancer. It is hard to define a specific 'good' or 'safe' diet but emphasizing green and yellow fruits and vegetables, reducing the number of total calories consumed and exercising regularly to achieve an ideal body weight are most likely to be helpful.

The contents of this health site are for informational purposes only. Always seek the advice of your physician or other qualified healthcare provider regarding any questions you may have about a medical condition.

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