Breast cancer
Risk factors

Topic Completed: 1 February 2012

Minor changes: 21 June 2020

Revised: 22 January 2019

Copyright: (c) 2002-2019,, Inc.

PubMed Search: Risk factors [title] breast cancer

Monika Roychowdhury, M.D.
Page views in 2019: 425
Page views in 2020 to date: 431
Cite this page: Roychowdhury M Risk factors. website. Accessed August 7th, 2020.
Definition / general

Genetic risk factors
  • First degree relatives with breast cancer; having one first degree relative (mother, sister, daughter) creates a relative risk of 2 - 3x, higher if relative is affected before age 50 or had bilateral disease (Int J Cancer 1997;71:800); relative risk with two first degree relatives is 4 - 6x
  • Li-Fraumeni syndrome (germline p53 mutations) - 25% of patients develop breast cancer
  • Mutations of BRCA1 and BRCA2 genes are associated with familial breast cancer at an early age, account for 20 - 60% of familial breast cancer, but only 5% of all cases
  • Cowden's disease (multiple hamartoma syndrome) - autosomal dominant, due to 10q mutation: 30 - 50% risk of breast cancer (DCIS or invasive ductal carcinoma) by age 50; also benign skin tumors (Hum Pathol 1998;29:47)
  • Heterozygous carriers for ataxia-telangiectasia have an 11% risk of breast cancer by age 50
  • Blacks (compared to whites) have more frequent breast cancers in women < age 40; present with higher stage tumors with higher nuclear grade that are more likely ER / PR negative, have higher mortality rate
  • Women have 100x risk of breast cancer compared to men

Hormone related risk factors
  • Early menarche
  • Late menopause
  • Nulliparity
  • Having first child after age 30
  • Postmenopausal women with obesity (BJOG 2006;113:1160) or estrogen producing ovarian tumors
  • Women using combined hormone replacement therapy with progestins, or estrogens alone (Int J Cancer 2007;121:645)
  • Risk with oral contraceptives is controversial, but see Mayo Clin Proc 2006;81:1290
  • Proposed mechanism of hormonal related risk factors is strong or prolonged estrogen stimulation, which may allow secretion of growth promoters

Factors associated with reduced risk of breast cancer:
  • Oophorectomy before age 35 or first child before age 18
  • Obesity prior to age 40 - due to anovulatory cycles and lower progesterone levels in late cycle

Environmental risk factors
Other risk factors
Additional references
Back to top