Breast Cancer Risk Factors

1. See Also
   1. Breast Cancer Risk Factors in Men
2. Breast Cancer Risk Resources
   1. Gail Model Breast Cancer Risk Calculator
      1. http://www.cancer.gov/bcrisktool/
   2. Extended Breast Cancer Risk Calculator (Steven Hall, MD)
      1. http://www.halls.md/breast/risk.htm
3. Risk Factors: Major
   1. Female Gender: 75% have no other known risk factors
   2. Age related Breast CancerIncidence in women
      1. Age 25 years = 1:19608 risk
      2. Age 30 years = 1:2525 risk
      3. Age 35 years = 1:622 risk
      4. Age 40 years = 1:217 risk
      5. Age 45 years = 1:93 risk
      6. Age 50 years = 1:50 risk
      7. Age 55 years = 1:33 risk
      8. Age 60 years = 1:24 risk
      9. Age 65 years = 1:17 risk
      10. Age 70 years = 1:14 risk
      11. Age 75 years = 1:11 risk
      12. Age 80 years = 1:10 risk
      13. Age 85 years = 1:9 risk
      14. Lifetime = 1:8 risk
   3. Reference
      1. Feuer (1993) J Natl Cancer Inst 85:892-7
4. Risk Factors: Other
   1. History of Breast Cancer
      1. Personal History
         1. Inversely related to Age
         2. Risk: 0.5% - 1% per year for at least 15 years
      2. Family History relative risk
         1. First Degree relative: 2.3 relative risk
            1. Unilateral/Postmenopausal: 1.2 relative risk
            2. Unilateral/Premenopausal: 1.8 relative risk
            3. Bilateral/Postmenopausal: 4.0 relative risk
            4. Bilateral/Premenopausal: 8.8 relative risk
         2. Second Degree relative: 1.5 relative risk
         3. Mother and Sister affected: 14.0 relative risk
      3. References
         1. Anderson (1985) Cancer 56:383
         2. Sattin (1985) JAMA 253
   2. Gene Mutations
      1. Most common types (>20 mutations have been identified)
         1. BRCA (BRCA1, BRCA2): 60% of Breast Cancer gene mutations
         2. AT (Ataxia telangiectasia) on Chromosome 11
      2. Associated risk
         1. Overall, these mutations account for only 3-5% of all Breast Cancers
         2. Cummulative lifetime risk of Breast Cancer in those with mutation: 25-85%
   3. Parity
      1. Age at first birth
         1. Age at first birth <20 years: 1.0 relative risk
         2. Age at first birth 20-24 years: 1.2 relative risk
         3. Age at first birth 25-29 years: 1.6 relative risk
         4. Age at first birth 30-35 years: 1.9 relative risk
         5. Age at first birth >35 years: 1.9 relative risk
         6. Nulliparous: 1.6 relative risk
      2. References
         1. Modified from McMahon based on Gail Model
         2. McMahon (1970) Bull World Health Organ 43:209-12
   4. Ethnicity
      1. Latinas may have higher Breast CancerIncidence
         1. Many of these latina patients were under age 35
         2. Also more aggressive Breast Cancer in this group
      2. References
         1. Biffl (2001) Am J Surg 182:596-600
   5. Hyperplasia on Breast Biopsy
      1. Fibrocystic Breast changes: No increased risk
      2. Hyperplasia
         1. No atypia: 2.0 relative risk
         2. Atypia (4% Incidence): 5.0 relative risk
   6. Increased Breast density
      1. Breast density >75% confers 4.7 odds ratio over those with Breast density <10%
         1. Boyd (2007) N Engl J Med 356(3): 227-36
5. Risk Factors: Other Risks
   1. Estrogen Replacement Therapy (ERT or HRT)
      1. Controversial (study results vary widely)
      2. Some studies show significant risk with >5 years use
         1. Risk increased by 40% (1.4 relative risk)
         2. Colditz (1995) New Engl J Med 332:1589-93
      3. Meta analysis shows no increased Breast Cancer risk
         1. Bush (2001) Obstet Gynecol 98:498-508
      4. HRT associated with reduced Breast Cancer mortality
         1. May be a result of earlier detection
         2. Bush (2001) Obstet Gynecol 98:498-508
   2. Tobacco abuse
      1. Does not appear to increase the risk of the primary Breast Cancer
      2. Does appear to increase pulmonary metastasis risk (Odds Ratio 1.96)
         1. Murin (2001) Chest 119:1635-40
   3. Alcohol
      1. Relative Risk increases 7% per drink consumed over 1 per day
      2. Hamajima (2002) Br J Cancer 87(11): 1234-45
   4. Red meat consumption
      1. Increased risk of Estrogen receptor positive cancer
      2. Relative risk: 1.97 for >1.5 red meat servings/day
      3. Cho (2006) Arch Intern Med 166:2253-9
   5. Overweight
      1. Postmenopausal weight gain >20 kg doubles Breast Cancer risk
      2. BMI >31 confers 1.6 fold increased Breast Cancer risk
6. Risk Factors: No effect on Breast Cancer risk
   1. Oral Contraceptives
      1. No (or minimal) increased Breast Cancer risk
      2. Reference
         1. Swanson (1992) J Am Med Womens Assoc 47:140-8
   2. Elective or Spontaneous Abortion
      1. No increased risk of Breast Cancer
      2. Reference
         1. Melbye (1997) JAMA 336:81-5
         2. Beral (2004) Lancet 363:1007-16
   3. Cummulative antibiotic use
      1. Was thought to be associated with Breast Cancer risk
         1. Velicer (2004) JAMA 291:827-35
      2. Other studies suggest no increased risk
         1. Kaye (2005) Epidemiology 16(5): 688-90
7. Risk Factors: Protective against Breast Cancer
   1. Lactation
      1. Risk decreases with 2 years of cumulative Lactation
      2. Affects premenopausal risk (not postmenopausal risk)
      3. Reference
         1. Newcomb (1994) N Engl J Med 338: 81-7
   2. Bilateral oophorectomy before age 50 years
      1. Cuts Breast Cancer relative risk by half
   3. Later onset Menarche
      1. Risk decreases 10% per every 2 years of Menarche delayed beyond age 12 years
   4. Exercise (greater risk reduction with increased duration and intensity)
      1. Premenopause: Breast Cancer relative risk drops up to 30%
      2. Postmenopause: Breast Cancer relative risk drops by up to 22%
   5. Selective Estrogen Receptor Modulators
      1. Tamoxifen
      2. Raloxifene (Evista)
8. References
   1. Steiner (2008) Am Fam Physician 78(12): 1361-6