Factors that modify breast cancer risk in women

Cancer prevention is action taken to lower the chance of getting cancer. Dr Nirasha Chiranjan lists the factors that modify breast cancer risk in women.

Breast cancer occurs in every country of the world in women at any age after puberty but with increasing rates in later life. It is a leading cause of mortality in women. In 2020, there were 2,3 million women diagnosed with breast cancer and 685 000 deaths globally.1 

As of the end of 2020, there were 7,8 million women alive who were diagnosed with breast cancer in the past five years, making it the world’s most prevalent cancer.

Approximately half of breast cancers can be explained by known risk factors, like reproductive factors and proliferative breast disease. An additional 10 percent are associated with family history and genetics. 

In addition, risk may be modified by demographic, lifestyle, and environmental factors. 

Risk factors2-7 

  • Increasing age
  • Female sex
  • Weight and body fat in post-menopausal women
  • Dense breast tissue
  • Benign breast disease
  • Hormone therapy
  • Early menarche and later menopause
  • Nulliparity
  • Tobacco and alcohol usage
  • Increasing age at first pregnancy
  • Family history of breast cancer
  • Genetic mutations
  • Previous exposure to ionizing radiation

Behavioural choices and related interventions that reduce the risk of breast cancer include:


The protective effect of breastfeeding has been shown in multiple studies. The magnitude of which depends on the duration of breastfeeding.

A large pooled analysis estimated that for every 12 months of breastfeeding, there was a 4,3% reduction in the relative risk of breast cancer.8 A postulated mechanism for the protective effect of breastfeeding is that it may delay the re-establishment of ovulatory cycles.

Regular physical activity and weight control

The risk of breast cancer is lower in physically active women compared to their least active counterparts. The reduction in breast cancer risk through physical activity may be from weight control and the effect that exercise plays on circulating hormonal influences.9


  • Low-fat dietary pattern in postmenopausal women. This pattern has been associated with reducing deaths following breast cancer diagnosis. The proposed mechanism is thought to be from a reduction in metabolic syndrome.
  • Diet rich in fruits and vegetables (Mediterranean diet) – plant based diets may decrease breast cancer risk.  
  • Diet high in fibre – studies show that dietary fibre intake is associated with a risk reduction in breast cancer incidence.10

Medical and surgical risk reduction strategies 

In women with a high-risk of breast cancer, chemoprevention with aromatase inhibitors in postmenopausal women, or tamoxifen in pre- or postmenopausal women, reduces breast cancer risks. Mastectomy also greatly decreases breast cancer risks and is an appropriate option for select patients at high-risk, for example BRCA carriers. 

Protect our mothers, sisters and daughters

To ensure we protect ourselves, our mothers, our sisters, our daughters, and many others, it is extremely important to be aware and talk about the dietary and behavioural interventions that are safe and effective ways to reduce breast cancer risk. 

Breast cancer is treated with a multi-disciplinary approach involving surgical oncology, radiation oncology, and medical oncology, which has been associated with a reduction in breast cancer mortality.

Cancer prevention is action taken to lower the chance of getting cancer. By preventing cancer, the number of new cases of cancer in a group or population is lowered. Hopefully, this will lower the number of deaths caused by cancer.


  1. Global Cancer Statistics 2020: GLOBOCAN Estimates of Incidence and Mortality Worldwide for 36 Cancers in 185 Countries Hyuna Sung PhD 04 February 2021
  2. Siegel RL, Miller KD, Fuchs HE, Jemal A. Cancer Statistics, 2021. CA Cancer J Clin 2021; 71:7.
  3. Chlebowski RT, Chen Z, Anderson GL, et al. Ethnicity and breast cancer: factors influencing differences in incidence and outcome. J Natl Cancer Inst 2005; 97:439.
  4. .Morimoto LM, White E, Chen Z, et al. Obesity, body size, and risk of postmenopausal breast cancer: the Women’s Health Initiative (United States). Cancer Causes Control 2002; 13:741.
  5. Nelson HD, Zakher B, Cantor A, et al. Risk factors for breast cancer for women aged 40 to 49 years: a systematic review and meta-analysis. Ann Intern Med 2012; 156:635.
  6. McCormack VA, dos Santos Silva I. Breast density and parenchymal patterns as markers of breast cancer risk: a meta-analysis. Cancer Epidemiol Biomarkers Prev 2006; 15:1159.
  7. Braithwaite D, Miglioretti DL, Zhu W, et al. Family History and Breast Cancer Risk Among Older Women in the Breast Cancer Surveillance Consortium Cohort. JAMA Intern Med 2018; 178:494.
  8. Collaborative Group on Hormonal Factors in Breast Cancer. Breast cancer and breastfeeding: collaborative reanalysis of individual data from 47 epidemiological studies in 30 countries, including 50302 women with breast cancer and 96973 women without the disease. Lancet 2002; 360:187.
  9. Hardefeldt PJ, Penninkilampi R, Edirimanne S, Eslick GD. Physical Activity and Weight Loss Reduce the Risk of Breast Cancer: A Meta-analysis of 139 Prospective and Retrospective Studies. Clin Breast Cancer 2018; 18:e601.
  10. Chlebowski RT, Aragaki AK, Anderson GL, et al. Association of Low-Fat Dietary Pattern With Breast Cancer Overall Survival: A Secondary Analysis of the Women’s Health Initiative Randomized Clinical Trial. JAMA Oncol 2018; 4:e181212.
Dr Nirasha Chiranjan is a radiation oncologist. 
Her special interests are breast, gynaecological, head and neck, and central nervous system 
cancers. She is based at the Life Flora Hospital, Sandton Oncology (Morningside) and Ahmed Kathrada Cancer Institute.

MEET THE EXPERT – Dr Nirasha Chiranjan

Dr Nirasha Chiranjan is a radiation oncologist. Her special interests are breast, gynaecological, head and neck, and central nervous system cancers. She is based at the Life Flora Hospital, Sandton Oncology (Morningside) and Ahmed Kathrada Cancer Institute.

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