Breast cancer is the second most common type of cancer among American women, just behind skin cancer. The disease occurs when cells in the breast grow out of control.

The breasts are composed of glands called lobules that produce milk, thin tubes called ducts that transport milk to the nipple, connective tissue consisting of fibrous and fatty tissue, lymph nodes, and blood vessels. Breast cancer usually starts in the ducts and is classified as ductal carcinoma, but the disease may also occur in other parts of the breast.

The vast majority of patients with breast cancer are women, with an estimated 292,000 new cases diagnosed in 2015 in the U.S. alone. However, men can also develop breast cancer.

After a diagnosis, it is normal for patients to question what caused the disease. The exact causes for breast cancer are still not fully understood, despite extensive research. In almost every case, a doctor is unable to determine the exact causes of the disease, but breast cancer itself is a result of damage to the DNA of a cell.

Breast Cancer Caused by Inherited Gene Mutations

Genetics can play an important part in the development of breast cancer; gene mutations may be inherited or acquired. There are specific DNA mutations that run in families and drastically increase the probability of breast cancer.

The most common mutations occur in the BRCA1 and BRCA2 genes, which are tumor suppressor genes. A mutation in one of the BRCA genes makes the gene unable to prevent abnormal growth, and these mutated genes can be inherited from a parent. Other genes that may inherit mutations and cause breast cancer include ATM, TP53, CHEK2, PTEN, CDH1, STK11, and PALB2.

According to theAmerican Cancer Society, genetic testing can identify some women who have inherited mutations in the BRCA1 or BRCA2 tumor suppressor genes. The mutations are considered ‘high-penetrance’ because they often lead to cancer. Still, most cases of cancer including breast cancer are not caused by mutations. More often, low-penetrance mutations or gene variations lead to cancer development. In spite of mutations or variant genes, the overall effect is significant due to commonality and  because more than one proposed cause is usually present at the same time.

Breast Cancer Caused by Acquired Gene Mutations

While many patients have family members who also had breast cancer, the vast majority of DNA mutations responsible for the development of the disease are not inherited and occur in single breast cells during a woman’s life.

Acquired mutations affecting the oncogenes or tumor suppressor genes are due to several factors, including radiation or exposure to cancer-causing chemicals. The exact causes are not known. Researchers believe many unknown factors cause DNA mutations.

In fact, several gene mutations occur. But tests to spot acquired gene changes, including too many copies of the HER2 oncogene which leads to an aggressive cancer, do exist. Drugs to target the cancers and improve prognosis are available.

Risk Factors That Impact Breast Cancer Development

Many risk factors increase the probability of breast cancer – some are  beyond a person’s control and others are lifestyle choices.

Risk factors s that cannot be changed are age, gender, race and ethnicity, breast tissue density, specific benign breast diseases, number of lifetime menstrual cycles, chest radiation, and exposure to the drug diethylstilbestrol (DES).

The lifestyle-related, or choice factor include having no children or a first child after the age of 30; oral contraceptive use; the birth control injection depot-medroxyprogesterone acetate (DMPA Depo-Provera); hormone therapy after menopause with estrogen and progesterone; alcohol consumption; smoking; being overweight or obese; and a sedentary lifestyle.

Additional suspected factors for breast cancer that currently cause lively debate among healthcare workers include diet and vitamin intake, chemicals in the environment, and night work.

Note: Breast Cancer News is strictly a news and information website about the disease. It does not provide medical advice, diagnosis, or treatment. This content is not intended to be a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your physician or other qualified health provider with any questions you may have regarding a medical condition. Never disregard professional medical advice or delay in seeking it because of something you have read on this website.