Revisiting Old Facts and Exploring New Data in Breast Cancer

Cancer remains a leading cause of death in the United States, having claimed nearly 600,000 lives in 2017, according to the CDC. Among the most common forms of cancer in the United States is breast cancer, the fourth most common form of cancer behind skin, lung, and prostate cancers, respectively.

Approximately 1 in 8 women living in the United States will develop an invasive form of breast cancer at some point in her life, and experts project that more than 268,000 new cases of breast cancer diagnosed in the United States will be invasive in nature in 2019. In fact, in early 2019, there were more than 3.2 million women with either a current or past medical history of breast cancer living in the United States.

Experts project the remaining 62,930 of new cases will be non-invasive, or in-situ, cancer. An estimated 30% of newly-diagnosed cancers in women are breast cancer.

Despite these numbers and the fact that breast cancer ranks second only to skin cancer in women, the incidence rate of breast cancer first began to decline in 2000. Experts attribute some of the decline to the decreased use of hormone replacement therapy observed after the publication of the Women’s Health Initiative in 2002. The paper was among the first of several studies published from 2002 to 2006, collectively known as the Women's Health Initiative Studies. The studies investigated the outcomes of estrogen and progestin and estrogen alone in postmenopausal women.¹ The findings of the first study suggested that women who receive estrogen plus progesterone therapy had an increased risk of various cardiovascular morbidities, such as coronary heart disease, venous thromboembolism, and stroke. They also faced a higher risk of developing invasive breast cancer.

There are few factors that can affect a woman's breast cancer risk in women, such as race, ethnicity, family history, and genetics. Breast cancer is more common among African American women than white women who are younger than 45 years of age. African American women are also more likely to succumb to the disease. Meanwhile, not only do women who are Asian, Hispanic, or Native American have a lower risk of receiving a breast cancer diagnosis, they are less likely to die from it.

Breast cancer risk almost doubles in women who have first-degree female relatives who have been diagnosed with the disease.  Still, the number of women who receive a breast cancer diagnosis and also have a relative diagnosed with the condition is less than 15%. Inheritable genetic mutations passed from the woman’s mother or father account for approximately 5-10% of breast cancers. Of these genes, BRCA1 and BRCA2 are the most common; the lifetime risk for breast cancer is almost 75% in women who carry the BRCA1 mutation.

The remainder of women diagnosed with breast cancer do not have a family history of the disease.

In addition to these statistics, new research from the National Institutes of Health draws a link between the use of permanent hair dyes, hair-straightening chemical, and breast cancer risk. Published in the International Journal of Cancer, the study found that women who used hair dye regularly in the year before enrolling in the study were 9% more likely to develop breast cancer than women who did not use permanent dye.² Black women who used permanent dyes every 5 to 8 weeks were 60% more likely to develop breast cancer. Their white counterparts who used permanent dyes regularly were only 8% more likely to develop the disease.

Regular use of chemical hair straighteners also increased risk. Women who used chemicals to straighten their hair every 5 to 8 weeks were more 30% more likely to develop cancer. The associations between white and African American women was similar.²

References:

1. Writing Group for the Women's Health Initiative Investigators. Risks and benefits of estrogen plus progestin in healthy-post menopausal women: Principal results from the Women's Health Initiative randomized controlled trial. JAMA. 2002. Doi: doi:10.1001/jama.288.3.321

2. Eberle CE, Sandler DP, Taylor KW, et al. Hair dye and chemical straightener use and breast cancer risk in a large US population of black and white women. Cancer Epidemiology. 2019. Doi: https://doi.org/10.1002/ijc.32738