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How common is breast cancer?

Breast cancer is the cancer diagnosed most frequently in Canadian women. About 25,000 new cases are diagnosed in Canadian women each year, representing about 26% of all new cancer in women. About 5,000 women die from the disease each year in Canada. Breast cancer can also affect men but it is not very common.

What is my risk of developing breast cancer?

One statistic that is often quoted is that women have a 1 in 9 or even 1 in 8 chance of developing breast cancer. This number is alarming and needs some explanation. While it's true that a woman has a 1 in 9 (or 11%) chance of developing breast cancer, 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, the next 5 years, or up to a certain age.

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

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

  • being female
  • having BRAC1 or BRAC2 gene mutations
  • having a family history of breast and other cancer
  • having a personal history of breast cancer
  • having dense breast tissue
  • being of Ashkenazi Jewish ancestry
  • having started menstruating before the age of 11
  • having gone through menopause after the age of 55
  • having received radiation therapy to the chest
  • having no children or having the first child after the age of 30
  • using oral contraceptives or hormone replacement therapy for a long time
  • drinking alcohol (risk increases with rising consumption)
  • being obese after menopause
  • having atypical hyperplasia (increased number of abnormal cells in the breast tissue)
  • having a rare genetic condition

Let’s have a look at some of the risk factors in detail.

Family history

Having one or more close relatives who had breast cancer increases your risk as well. Having first-degree relatives (mother, sister, or daughter) with breast cancer increases your risk more than second-degree relatives (grandmother, aunt, or niece). The risk is higher if the cancer was diagnosed in your relative before menopause.

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 11) and ended late (after age 55)
  • if you have not been pregnant or if you were older than 30 years old at the birth of your first child. An early first full-term pregnancy (before age 20) seems to have a protective effect on the cells in the milk ducts, and women who have had one have a lower-than-average risk 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.

Ivo Olivotto, MD 
in association with the MediResource Clinical Team 
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