Modifiable and Non-Modifiable Risk Factors for Breast Cancer
Breast cancer risk factors may be modifiable or non-modifiable. Modifiable risk factors are those that are related to lifestyle factors. Whereas, non-modifiable are ones that are related to genetic factors, age, ethnicity, etc.
Hormonal causes may be included in both. Like early menarche or late menopause comes under non-modifiable, whereas, intake of hormone replacement therapy, late marriage or late childbirth and obesity come under modifiable risk factors.
Below are some common modifiable and non-modifiable risk factors for breast cancer.
- Genetic factors – mutations in BRCA1 or BRCA2; 50-60% of women inheriting a BRCA1 mutation from either parent will have breast cancer by age 70
- Family history of breast cancer (not related to BRCA mutations)
- Personal history of hyperplastic breast disease
- Race: incidence is higher in Caucasian compared with African-American, Hispanic or Asian women
- Radiation treatment: chest irradiation as a child/young woman can significantly increase risk of developing breast cancer
- Menstrual history: early menarche (<12 yr) or late menopause (>50yr) has some association with increased risk. Also nulliparous, or first childbirth at >30 yrs.
- Oral contraceptives
- Hormone replacement therapy – >5 years of therapy with combined estrogen and progesterone may increase risk
- Not breast feeding
- Diet and obesity; physical inactivity
- Alcohol – 2-5 drinks/day can increase risk x 1.5 over non-drinkers.
Modifiable Risk Factors of Breast Cancer
Now let’s discuss the modifiable risk factors of breast cancer in detail-
It has been reported that women who get married and have children by the age of 26 years are generally at lower risk of developing breast cancer. While women who got married at a later age and have pregnancy after 35 years of age or who never have had a full-term pregnancy are at increased risk of developing breast cancer. Inadequate breastfeeding also increases the risk of the disease.
Breastfeeding is an important modifiable risk factor for breast cancer. It has been found to have health benefits for both mother and the child. Studies have shown an inverse relationship between breastfeeding and premenopausal breast cancer. Apart from breast cancer, women who do not breastfeed are also at higher risk of ovarian cancer, obesity, type 2 diabetes, metabolic syndrome, etc.
Prolonged hormonal replacement therapy (HRT)
Women who are using or who have used hormone replacement therapy (HRT) after menopause for many years are generally at higher risk of developing breast cancer. Although HRT intake helps in relieving postmenopausal symptoms, like hot flusher and night sweats, it has found to increase the risk of breast cancer, ovarian cancer and cardiovascular comorbidities.
The risk of breast cancer increases with with the duration of intake of HRT. Increased risk starts after 1 year of intake of HRT and may remain for more than 10 years after they have stopped taking it. Combined progesterone and estrogen containing HRT has greater risk compared to estrogen only.
Intake of oral contraceptives has been found to increase the risk of breast and cervical cancer. On the other hand, it may reduce the incidence of colorectal, ovarian and endometrial cancer.
Irrespective of the duration of intake, women have a higher risk of breast cancer if they have ever used oral contraceptives. The risk does not increase with the duration of OCP intake, and declines after stopping it’s intake.
Overweight or obese females are at higher risk of developing breast cancer which may be due to the higher exposure to estrogen produced in the fat tissue after menopause. Actually, after menopause, ovaries stop producing estrogen. So fat is major source of estrogen production due to activity of enzyme aromatase.
Increased obesity leads to an increase estrogen production that acts on breast cancer cells and increases their growth rate, thereby increasing the risk of breast cancer in postmenopausal women.
Moreover, excessive visceral fat may lead to excess inflammation due to low oxygen environement. This may also be a trigger for breast cancer development.
Studies have shown that smoking causing an increased risk of breast cancer, mainly hormone receptor positive breast cancer. It doesn’t increase the risk of triple negative breast cancer.
Smoking also causes poor outcomes in breast cancer patients with increased breast cancer specific mortality.
Excessive alcohol consumption has been reported to increase the risk of breast cancer and the risk increases with the increase in the amount of alcohol consumed. Studies have shown 15% higher risk of breast cancer in women who have 3 alcoholic drinks per week.
It may increase the risk of hormone receptor positive breast cancer by increasing the level of estrogens. Another mechanism is damaging the DNA in breast cancer cells.