October is Breast Cancer Awareness Month

Breast Cancer Awareness Month: Hormones & Cancer Growth

October is Breast Cancer Awareness Month. This is a good time to learn more about breast cancer and how it affects the body, risk factors, prevention, and treatment. Breast cancer occurs when cells in the breast begin to grow out of control. Breast cancer can start in one breast or both. While breast cancer occurs mostly in women, it can affect men as well.

About Breast Cancer

Breast cancer is the most common cancer for women in the United States, apart from skin cancer. Breast cancer accounts for about 1 in 3 new cancers diagnosed in women each year. The lifetime risk of a woman developing breast cancer is about 13 percent, or 1 in 8. Breast cancer is the second leading cause of cancer death for women. More than 43,000 women will die from breast cancer in the United States in 2023. 

There are different types of breast cancer, and the type depends on the part of the breast where the cancer begins. Lobules are glands in the breast that make milk. Lobular cancer begins in lobules. Ducts are small canals that come out of lobules and carry milk to the nipple. Ductal cancers begin in the ducts. Less common breast cancers can begin the nipple, fat and connective tissue, and blood or lymph vessels in the breast. Breast cancers can spread if cells reach the blood or lymph systems where they can then spread to other parts of the body. 

While it isn’t known exactly what causes breast cancer, there are certain risk factors. Family history of breast cancer and specific genes or gene changes, or mutations, are risk factors for breast cancer. Gene mutations can be passed down, or they can occur on their own. BRCA genes are tumor suppressor genes. These genes control how often cells divide. For those with inherited or acquired BRCA gene mutations, this suppressing ability can be changed or turned off. The gene no longer controls cell growth and division, and cancer is more likely to develop as a result. Other breast cancer risk factors include age, alcohol use, physical activity, race/ethnicity, birth control use, not having children, and not breastfeeding. There are several different treatment options for breast cancer. The most common treatment is surgery. Other types of treatment include radiation, chemotherapy, targeted drug therapy, and immunotherapy. 

Hormones & Breast Cancer

Another type of treatment is hormone therapy. Hormones are chemical substances in the body that travel to parts of the body, such as cells, organs, and tissues, and send messages and regulate functions. Tumor growth can be fueled by hormones for certain cancers, such as breast cancer, ovarian cancer, and prostate cancer. For breast cancer, tumor growth can be fueled by the hormones estrogen and progesterone. These hormones are found in all bodies but are most significant in their effects on female bodies, especially around reproductive function and pregnancy. About 65-75 percent of breast cancers are linked to hormones. Breast cancers that are dependent on hormones are often called HR-positive breast cancer. This means that a tumor contains hormone receptors. 

Hormone Therapy Research

A link between hormones and breast cancer was first explored in the late 1800s. In 1896, an article was published that described a new treatment for breast cancer called ovarian ablation. Ovarian ablation lowers or stops production of estrogen in the body through changes to the ovaries. The ovaries are female reproductive organs that release eggs and secrete hormones like estrogen and progesterone. In the 1800s, ovarian ablation occurred by surgically removing the ovaries completely. This quickly and permanently stopped production of estrogen and progesterone in the body. The first randomized clinical trials of ovarian ablation occurred in the 1940s, and these trials found that ovarian ablation reduced cancer recurrence and increased survival for breast cancer patients under the age of 50. These trials helped establish that ovarian function and hormone production were linked to breast cancer development and tumor growth in women. 

Alternative methods of reducing or stopping estrogen and progesterone in the body were explored in the 1900s, especially those that could be less invasive and risky than surgery. A medication that could block estrogen activity, called tamoxifen, was discovered and tested in multiple clinical trials in the 1970s. In one study, tamoxifen was given to 59 women with breast cancer twice a day for two months. Researchers found that 32 percent of patients had tumors that either fully or partially resolved from the treatment with only mild side effects. Tamoxifen was approved by the Food & Drug Administration (FDA) in 1977. Tamoxifen was a breakthrough breast cancer treatment. It is often used alongside surgery or chemotherapy and has been found to dramatically decrease breast cancer recurrence and increase survival rates. 

Tamoxifen is also used to prevent breast cancer in certain women with a high risk of developing breast cancer, such as a family history or genetic mutations. A large study in the 1990s tested this by recruiting and randomly assigning more than 13,000 women with high risk of developing breast cancer to receive either tamoxifen or a placebo for five years. After five years, researchers found that the women who took tamoxifen had a 49 percent lower risk of developing invasive breast cancer and 50 percent lower risk of developing noninvasive breast cancer than those who took the placebo. 

In the 2000s, another type of medication that impacts estrogen was developed called aromatase inhibitors. These drugs block an enzyme the body needs to make estrogen. These drugs work differently than tamoxifen but are similarly or more effective and typically result in fewer side effects. Aromatase inhibitors and tamoxifen are now considered standard of care for many types of breast cancer. 

Breast Cancer Prevention

It is important to consider cancer prevention during Breast Cancer Awareness Month. While many cases of breast cancer cannot be prevented, there are some lifestyle strategies to lower your risk. Some ways to lower your risk include maintaining a healthy weight, being physically active, and limiting alcohol use. For those with a family history and/or inherited gene changes, some prevention strategies include genetic testing and counseling, certain medications like tamoxifen, preventive surgery, and close observation. Regular breast cancer screening is also important to be able to catch abnormalities or cases early.