Lifestyle and other Environmental Factors Involved in Breast Cancer

Breast cancer epidemiology pattern differences across countries are further compounded by:
- Cultural factors, lifestyle factors and national awareness campaigns
The increase in breast cancer incidence between 1980 and the late 1990s:
- Is likely due to:
  - Changes in reproductive factors:
    - With advanced maternal age for first pregnancy,
  - An increase in awareness and mammography screening
- Several explanations have been offered as to why early pregnancy and high levels of estrogen during pregnancy reduce breast cancer risk:
  - The proposed mechanisms include:
    - Altered sensitivity of the mammary gland to:
      - Later hormonal exposures
    - Reduction in the number of stem or progenitor cells:
      - Consequently, elimination of targets for malignant transformation
    - Changes in gene expression patterns:
      - Resulting in reduced proliferation and increased differentiation
Other risk factors for breast cancer include:
- Early menarche:
  - Before 12 years of age
- Lack of breast feeding
- Late-onset menopause:
  - After 55 years of age
It has been estimated that approximately 20% of breast cancers worldwide:
- Can be attributed to modifiable risk factors, including:
  - Obesity
  - Physical inactivity
  - Alcohol use:
    - Offering the potential for reduction in the disease burden by promoting a healthy lifestyle:
      - For example, each 10 g (roughly one drink) of alcohol consumed daily by an adult woman:
        Will lead to a 7% to 10% increase in breast cancer risk:
        This association is observed in both premenopausal and postmenopausal women
    - Furthermore, the influence of central obesity on breast cancer risk and survival has been studied:
      - Current evidence suggests a stronger adverse effect of obesity on breast cancer risk and survival in women of Asian ancestry than in non-Hispanic white women in the United States and Europe
      - Central obesity seems to have a stronger influence on breast cancer risk:
        In African-American women than general adiposity as measured by body mass index (BMI)
      - Currently, 18% of premenopausal women in the United States have elevated BMI and breast density:
        And may benefit from lifestyle modifications involving weight loss and exercise:
        However, this benefit is not limited to premenopausal women, especially when the Asian breast cancer population is being studied:
        For example, it was noted that postmenopausal Asian women whose BMI increased ≥ 5.0 were significantly more likely to develop breast cancer than those with a stable BMI (defined as a change in BMI of ±2.5)
        Additionally, postmenopausal women with abdominal circumference ≥ 90 cm were significantly more likely to develop breast cancer than those with abdominal circumference < 70 cm
        Among postmenopausal women with BMI ≥ 20:
        Those with high (≥ 6.5) glycated hemoglobin (HbA1c) were more likely to develop breast cancer than those with low (< 5.5) HbA1c:
        Thus, breast cancer incidence, obesity and increased BMI are associated in postmenopausal Asian women
      - The possibility that the use of hormonal contraceptives:
        May increase the risk of breast cancer has been raised for many years
        Two recent papers showed a statistically significant increase in breast cancer with use of hormonal contraception:
        Even contemporary lose-dose formulations
        Thus, counselling may be needed to encourage women of child-bearing age to adopt lifestyle habits that may reduce the cancer risk
- Studies have shown that the risk for breast cancer is due to a combination of factors:
  - The main factors that influence the risk include being a woman and getting older
  - Most breast cancers are found in women who are 50 years old or older
- Some women will get breast cancer even without any other risk factors that they know of:
  - Having a risk factor does not mean you will get the disease, and not all risk factors have the same effect
  - Most women have some risk factors, but most women do not get breast cancer
- Risk Factors that Cannot be Changed:
  - Getting older:
    - The risk for breast cancer increases with age
    - Most breast cancers are diagnosed after age 50
  - Genetic mutations:
    - Inherited changes (mutations) to certain genes, such as BRCA1 and BRCA2:
      - Women who have inherited these genetic changes are at higher risk of breast and ovarian cancer
  - Reproductive history
    - Early menstrual periods before age 12 and starting menopause after age 55:
      - Expose women to hormones longer:
        Raising their risk of getting breast cancer
  - Having dense breasts:
    - Dense breasts have more connective tissue than fatty tissue:
      - Which can sometimes make it hard to see tumors on a mammogram
      - Women with dense breasts are more likely to get breast cancer
  - Personal history of breast cancer or certain non-cancerous breast diseases:
    - Women who have had breast cancer are more likely to get breast cancer a second time
    - Some non-cancerous breast diseases such as atypical hyperplasia or lobular carcinoma in situ:
      - Are associated with a higher risk of getting breast cancer
  - Family history of breast or ovarian cancer:
    - A woman’s risk for breast cancer is higher if she has a mother, sister, or daughter (first-degree relative) or multiple family members on either her mother’s or father’s side of the family who have had breast or ovarian cancer
    - Having a first-degree male relative with breast cancer also raises a woman’s risk
  - Previous treatment using radiation therapy:
    - Women who had radiation therapy to the chest or breasts (like for treatment of Hodgkin’s lymphoma) before age 30 have a higher risk of getting breast cancer later in life
  - Women who took the drug diethylstilbestrol (DES):
    - Which was given to some pregnant women in the United States between 1940 and 1971 to prevent miscarriage, have a higher risk
    - Women whose mothers took DES while pregnant with them are also at risk
Risk Factors You Can Change:
- Not being physically active:
  - Women who are not physically active have a higher risk of getting breast cancer
- Being overweight or obese after menopause:
  - Older women who are overweight or obese have a higher risk of getting breast cancer than those at a normal weight
- Taking hormones:
  - Some forms of hormone replacement therapy (those that include both estrogen and progesterone) taken during menopause can raise risk for breast cancer when taken for more than five years
  - Certain oral contraceptives (birth control pills) also have been found to raise breast cancer risk
- Reproductive history:
  - Having the first pregnancy after age 30
  - Not breastfeeding
  - Never having a full-term pregnancy can raise breast cancer risk
- Drinking alcohol:
  - Studies show that a woman’s risk for breast cancer increases with the more alcohol she drinks
Research suggests that other factors such as:
- Smoking, being exposed to chemicals that can cause cancer, and changes in other hormones due to night shift working also may increase breast cancer risk