1. Demographics and Risk Factors

Author: Dr. Nathalie Levasseur
Date of completion: April 2026
Date of next review: May 2027

See Breast Clinical Care Pathway

Breast cancer is a leading cancer in women in all countries. Anticipated average lifetime risk is 1 in 8.1,2

A summary of known risk factors for breast cancer is shown in Table 1 below, which also indicates the strength of the risk factor in the development of breast cancer.3

Table 1: Risk factors associated with breast cancer

Modifiable risk factors

  • Obesity
  • Physical activity
  • Alcohol consumption
  • Diet
  • Smoking
  • Hormone replacement therapy (long term usage, systemically absorbed)

Non-modifiable risk factors

  • Personal history of breast cancer
  • Family history of breast cancer (including males)
  • Genetic mutations (Hereditary Cancer & High Risk Clinic)
  • Female sex at birth
  • Older age
  • Nulliparity
  • Older age at first birth (over age 30)
  • Early menstruation & delayed menopause
  • Socioeconomic status
  • Race/ethnicity
  • Prior breast abnormality requiring biopsy
  • Increased breast density
  • Prior chest wall radiotherapy treatment
  • Breastfeeding (potentially protective) *evidence conflicting*

References

  1. Public Health Agency of Canada. Breast cancer. https://www.canada.ca/en/public-health/services/chronic-diseases/cancer/breast-cancer.html. Accessed 2026 Apr 29.
  2. Canadian Cancer Society. Breast cancer statistics. https://cancer.ca/en/cancer-information/cancer-types/breast/statistics. Accessed 2026 Apr 29.
  3. Łukasiewicz S, Czeczelewski M, Forma A, Baj J, Sitarz R, Stanisławek A. Breast Cancer-Epidemiology, Risk Factors, Classification, Prognostic Markers, and Current Treatment Strategies-An Updated Review. Cancers (Basel). 2021 Aug 25;13(17):4287. doi: 10.3390/cancers13174287. PMID: 34503097; PMCID: PMC8428369​