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1. Demographics and Risk Factors

Updated February 2016

Breast cancer is the most common life-threatening cancer among women in British Columbia and the second most common cause of cancer mortality. Age-standardized incidence rates increased somewhat over the 15 year period from 1977-1991,  declined slightly for 10 years, and now are essentially stable. Mortality from breast cancer appears to have decreased by 30% over the last decade in British Columbia, Canada, the US and UK. The reasons for this decline appear multifactorial and are likely a combination of screening, earlier diagnosis and multi-disciplinary care including more adjuvant therapy. In British Columbia, the estimated number of cases for the year 2012 was 3200.  This number is estimated to be 3400 in 2015. Although breast cancer is more frequently seen in older women, due to the demographics of the population, the actual number of women diagnosed with breast cancer is highest in the 50-60 year age range. 

Numerous risk factors for breast cancer have been well established, including age, mammographic density, nulliparity or late age at first birth, early menarche, late menopause, and use of hormonal replacement therapy. All these factors increase risk, while early age at first delivery, physical activity and lactation appear to reduce risk. 

There is growing evidence that premenopausal and post-menopausal breast cancer may be different entities. International differences in breast cancer incidence curves have led to the hypothesis that environmental factors predominantly influence the development of postmenopausal breast cancer whereas genetic and other endogenous factors predominantly influence premenopausal breast cancer.

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.

Table 1. 

Risk Factors Associated with Breast Cancer by Level of Risk

Weak risk factors for breast cancer (RR <2)

  • Family history of postmenopausal breast cancer, except if associated with male breast cancer + bilateral disease
  • High Socioeconomic status
  • Nulliparity
  • Later age at first birth (> 30 yr vs >20 yr)
  • Later age at menopause (>55 yr vs >45 yr)
  • Early age at menarche (<11 yr vs >15 yr)
  • Postmenopausal obesity
  • Alcohol consumption
  • Diet
  • Hormone replacement therapy (long term usage)
Moderate risk factors for breast cancer (RR 2-4)

  • Older age
  • North American and Northern European residence
  • Family history of premenopausal breast cancer
  • Personal history of breast cancer
  • Breast hyperplasia without atypia
  • Mammographic density occupying >50% of the breast volume
Strong risk factors for breast cancer (RR>4)

  • Family history of premenopausal bilateral breast cancer or premenopausal breast cancer in mother, grandmother, sister, daughter and aunt or DEL of ovarian cancer in mother, grandmother, sister, aunt or of male breast cancer or of breast cancer at any age in multiple (≥3) female relatives
  • Evidence of susceptibility gene including, but not restricted to, BRCA1/ BRCA2, PTEN, TP53, CDH1, STK11, PALB2
  • Personal history of lobular carcinoma in situ
  • Breast atypical hyperplasia
  • Mammographic density occupying > 75% of the breast volume
Reference: (BC Med J 1997;39:496-500)

SOURCE: 1. Demographics and Risk Factors ( )
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