One third of postmenopausal breast cancers are preventable because of modifiable risk factors.

https://upload.wikimedia.org

Modifiable risk factors account for a large proportions of breast cancer cases and Identification of this factors is the key to bring down the incidence of postmenopausal breast cancer says the result of a study published in December issue of American Journal of Epidemiology. [1]

This study mainly focused on those population based risk factors that are modifiable at menopause.

Incidence of breast cancer vary across the globe and geographical variation in prevalence rate suggest that modifiable risk factors play a role in its causation.

www.nationalbreastcancer.org

Out of multiple population attributable risk factors identified some are non-modifiable like height, BMI, family H/O breast cancer, prior benign breast lump and reproductive factors such as parity, age at first birth and reproductive life span.

This study analyzed the data from Nurses Health study that spanned over 20 years from 1980-2010.   It was seen that 8,421 cases of postmenopausal breast cancer developed out of 121,700 women in the study.[2]

When all the risk factors were analyzed and controlled for age, the PAR% for developing breast cancer was 70%. Population Attributable Risk (or Population Attributable Fraction) indicates the number (or proportion) of cases that would not occur in a population if the factor were eliminated.

That means 70% of cases of breast cancer developed in patients who had known risk factors for the disease other than age. Majority of these attributable risk factors were non-modifiable but nearly one third were modifiable. Greatest risk was seen in patients who gained a substantial weight at age 18.

CDC.gov

The modifiable Population Attributable Risk(PAR) factors identified in the study are weight change since age 18 years, alcohol consumption, physical activity level, breastfeeding, and menopausal hormone therapy use.

Changes in these 5 modifiable risk factors could reduce the rate by 34%.

Variations in the non-modifiable risk factors among different geographical locations explain the large variation in incidence of the disease across international borders.

 To conclude, keeping the weight gain to minimum, no drinking, high physical activity, breast feeding and no hormone replacement therapy was responsible for population attributable risk percentages (PAR%) of 34%, it was moderately higher for ER+ (PAR% = 39.7%) than ER–breast cancers (PAR% = 27.9%).

Breast cancer is a major cause of morbidity and mortality worldwide and it is most common cancer in women in US. Some statistics about breast cancer in US by breastcancer.org are:

• About 1 in 8 U.S. women (about 12%) will develop invasive breast cancer over the course of her lifetime and more than 77% occur in women over the age of 50 years.
• About 85% of breast cancers occur in women who have no family history of breast cancer. 
• In 2017, an estimated 255,180 new cases of invasive breast cancer are expected to be diagnosed in women in the U.S., along with 63,410 new cases of non-invasive (in situ) breast cancer.
• About 40,610 women will die from breast cancer in 2017.

---

[1] https://academic.oup.com/aje/article-abstract/184/12/884/2645430/Population-Attributable-Risk-of-Modifiable-and?redirectedFrom=fulltext

[2] http://www.nurseshealthstudy.org/