What causes breast cancer

Overview

Breast cancer is a complex disease that arises when cells in the breast begin to grow uncontrollably, forming a tumor. These tumors can be benign (non-cancerous) or malignant (cancerous). Malignant tumors can invade surrounding tissues and spread (metastasize) to other parts of the body. The vast majority of breast cancers begin in the ducts or lobules of the breast. Ductal carcinoma originates in the milk ducts, while lobular carcinoma starts in the lobules, the glands that produce milk. Understanding the causes of breast cancer involves looking at a combination of genetic predispositions and environmental and lifestyle influences.

Genetic Factors

A significant factor in breast cancer development is genetics. While most breast cancers are sporadic, meaning they occur by chance without a specific inherited cause, a portion (estimated between 5-10%) are hereditary. This means they are linked to inherited mutations in certain genes that significantly increase a person's risk of developing cancer. The most well-known genes associated with hereditary breast cancer are BRCA1 and BRCA2. Mutations in these genes are responsible for a large percentage of inherited breast and ovarian cancers. Other genes, such as TP53, PTEN, and ATM, have also been linked to increased breast cancer risk. When these genes are mutated, they often fail to properly repair DNA damage or control cell division, leading to the accumulation of mutations and potentially cancer. If a close relative (mother, sister, daughter) has had breast cancer, especially at a young age or in both breasts, a person's risk of carrying a hereditary mutation increases.

Age and Hormonal Influences

Age is one of the most significant non-genetic risk factors for breast cancer. The incidence of breast cancer rises sharply after the age of 50. This is partly due to the cumulative effect of environmental exposures and DNA damage over a lifetime, as well as natural hormonal changes associated with aging. Hormonal factors also play a crucial role. Breast cells are sensitive to hormones, particularly estrogen and progesterone. Exposure to these hormones, especially over long periods, can stimulate the growth of breast cells, including any that may have become cancerous. Factors that increase cumulative estrogen exposure include:

• Starting menstruation at an early age (before age 12)
• Experiencing menopause at a later age (after age 55)
• Never having had children or having the first child after age 30
• Using hormone replacement therapy (HRT) after menopause, particularly combined estrogen-progestin therapy.

Conversely, factors that decrease exposure, such as early pregnancy, breastfeeding, and early menopause, can be protective.

Lifestyle and Environmental Factors

A variety of lifestyle choices and environmental exposures can influence breast cancer risk. These factors often interact with genetic predispositions and hormonal influences.

• Diet and Weight: Being overweight or obese, especially after menopause, is a significant risk factor. Fat tissue is a source of estrogen, so more fat tissue means higher estrogen levels. A diet high in saturated fats and low in fruits and vegetables may also contribute.
• Physical Activity: A lack of regular physical activity is associated with an increased risk of breast cancer. Exercise helps maintain a healthy weight, can reduce hormone levels, and may directly affect cancer cell growth.
• Alcohol Consumption: The risk of breast cancer increases with the amount of alcohol consumed. Even moderate drinking can increase risk, and the risk rises with higher intake.
• Smoking: While traditionally linked more strongly to lung cancer, smoking is now recognized as a risk factor for breast cancer, especially in younger women and postmenopausal women.
• Radiation Exposure: Exposure to ionizing radiation, such as from radiation therapy for other cancers (especially to the chest area during adolescence or young adulthood), significantly increases the risk of developing breast cancer later in life.
• Certain Chemical Exposures: Research is ongoing into the potential links between certain environmental chemicals (e.g., pesticides, industrial pollutants, chemicals in plastics) and breast cancer risk, though definitive links are still being investigated.

Other Factors

Other factors that can influence breast cancer risk include:

• Dense Breast Tissue: Women with dense breasts (more glandular and fibrous tissue and less fatty tissue) have a higher risk of developing breast cancer. Dense breasts can also make it harder to detect tumors on mammograms.
• Previous Breast Conditions: Certain non-cancerous breast conditions, such as atypical hyperplasia, are associated with an increased risk of breast cancer.
• Family History: A personal or family history of breast cancer, particularly in close relatives (mother, sister, daughter) or in multiple family members, increases risk. This is often related to inherited genetic mutations but can also reflect shared environmental or lifestyle factors.

It's important to note that having one or more risk factors does not guarantee that a person will develop breast cancer. Conversely, many women diagnosed with breast cancer have no identifiable risk factors other than being female and aging. Ongoing research continues to explore the intricate interplay of genetics, environment, and lifestyle in the development of this disease.