Colon cancer, a type of colorectal cancer, begins in the large intestine. Understanding its contributing factors is important for prevention and early detection. While many risk factors affect both sexes, some are particularly relevant to women. This article explores the causes of colon cancer, focusing on factors influencing risk in women.
General Risk Factors
Several broad factors contribute to the likelihood of developing colon cancer. Age is a primary consideration, as the risk generally increases after 50 years old, though diagnoses among younger individuals have notably risen. Lifestyle choices also play a substantial role, with dietary habits being particularly impactful. Consuming diets high in red and processed meats, low in fiber, and rich in unhealthy fats and calories can elevate risk. Conversely, a diet abundant in fruits, vegetables, and whole grains may offer protection.
Maintaining a healthy weight is important, as excess body weight increases the risk of developing and dying from colon cancer. Physical inactivity is associated with a higher risk, indicating that regular physical activity can be protective. Smoking and alcohol consumption are recognized contributors; long-term tobacco use increases risk, and even moderate alcohol intake has been linked to an elevated chance of developing colon cancer. A personal or family history of colon cancer or precancerous polyps further raises an individual’s risk, especially if a first-degree relative was diagnosed at a younger age.
Genetic Predispositions
Inherited genetic conditions account for a smaller but significant portion of colon cancer cases, typically around 5%. These conditions involve specific gene mutations passed down through families, leading to a much higher likelihood of cancer at an earlier age. Lynch Syndrome, also known as hereditary nonpolyposis colorectal cancer (HNPCC), is the most common inherited form. This syndrome arises from mutations in DNA mismatch repair (MMR) genes, such as MLH1, MSH2, MSH6, PMS2, and EPCAM.
Individuals with Lynch Syndrome face a substantially increased lifetime risk of colon cancer, with estimates ranging from 40% to 80%, and for women, a 40% to 60% risk. Cancers associated with Lynch Syndrome often develop in the 20s or 30s and are frequently found on the right side of the colon. Beyond colon cancer, Lynch Syndrome also elevates the risk for other cancers, including endometrial and ovarian cancers. Familial Adenomatous Polyposis (FAP) is another inherited condition, causing individuals to develop hundreds to thousands of precancerous polyps in the colon, which can become cancerous if not detected and removed.
Factors Unique to Women
Hormonal factors play a distinct role in colon cancer risk for women. Postmenopausal hormone therapy (MHT or HRT), used to manage menopausal symptoms, has been consistently associated with a reduced risk of colorectal cancer. Studies indicate a risk reduction ranging from 20% to 40% among women who use HRT, particularly current or long-term users. This protective effect has been observed with both estrogen-only therapy and combined estrogen-plus-progestin regimens.
The influence of endogenous estrogen levels also appears significant. Pre-menopausal women generally have a lower risk of colon cancer compared to men of the same age, and the risk tends to increase around menopause. Higher levels of endogenous estradiol in postmenopausal women, not on HRT, have been linked to a decreased risk of colon cancer, suggesting a protective effect of naturally occurring estrogen. While the role of reproductive history, such as the number of pregnancies, has been explored, scientific findings remain conflicting and do not present a clear, consistent association.
Inflammatory Bowel Conditions
Chronic inflammatory bowel diseases (IBD), ulcerative colitis and Crohn’s disease, are recognized as significant risk factors for colon cancer. The persistent inflammation associated with these conditions can damage genetic material within colon cells, leading to mutations and promoting cancerous tumor growth. The risk of developing colon cancer in individuals with IBD increases with the duration and extent of inflammation.
For example, the risk of colon cancer in ulcerative colitis patients is estimated at 2% after 10 years, 8% after 20 years, and 18% after 30 years of disease. Crohn’s disease, particularly when it affects the colon, also elevates the risk. Factors such as a diagnosis at a younger age, widespread inflammation, and the presence of primary sclerosing cholangitis can further increase this risk for IBD patients. Despite the elevated risk, most individuals with IBD do not develop colorectal cancer, partly due to improved screening practices and more effective inflammation management.