A polyp is an abnormal growth of tissue that projects from a mucous membrane, the moist lining found inside many organs of the body. These growths are quite common, frequently appearing in the colon, nose, and uterus, though they can develop anywhere a mucous membrane exists, such as the stomach or sinuses. While most polyps are benign, they represent a deviation from normal tissue growth, and certain types have the potential to turn cancerous over time. Understanding the reasons behind this abnormal proliferation, from the microscopic level of the cell to the influence of genetics and lifestyle, helps to explain why polyps form.
Cellular and Molecular Basis of Polyp Growth
Polyps fundamentally arise from a malfunction in the highly regulated processes of cell life, division, and death. Normally, cells follow an orderly cycle of renewal, where old cells die off and are replaced by new ones. Polyp formation begins when cells acquire genetic errors, known as somatic mutations, that disrupt this balance, leading to uncontrolled cell proliferation.
This cellular overgrowth is often triggered by changes in specific genes that govern cell behavior. A primary example is the Adenomatous Polyposis Coli (APC) gene, a tumor suppressor responsible for preventing cells from growing out of control. When the APC gene is inactivated by mutation, a protein called beta-catenin accumulates in the cell nucleus, which then activates genes that promote cell division and growth.
The progression from a normal cell to a polyp, and potentially to cancer, is a multi-step process driven by the accumulation of additional mutations. Beyond the initial inactivation of a tumor suppressor like APC, activating mutations in oncogenes, such as KRAS, can occur. Oncogenes, when mutated, actively promote cell growth. The combined effect of losing tumor suppression and gaining growth promotion results in the formation of a visible polyp.
Hereditary and Non-Modifiable Risk Factors
Some causes of polyp development are inherited through genetics or related to factors beyond an individual’s control. Age is a significant non-modifiable risk factor, with the likelihood of developing polyps, particularly in the colon, increasing substantially as a person gets older. This extended time allows for more opportunities for somatic mutations to accumulate in cells, driving polyp formation.
Certain inherited genetic syndromes dramatically increase the risk of developing numerous polyps, often at a young age. Familial Adenomatous Polyposis (FAP) is an autosomal dominant condition caused by an inherited mutation in the APC gene. Individuals with FAP typically develop hundreds to thousands of polyps, nearly guaranteeing the development of colorectal cancer if the colon is not removed.
Lynch Syndrome is the most common inherited cause of colorectal cancer predisposition. This syndrome is caused by inherited mutations in DNA mismatch repair genes, which normally correct errors made during DNA replication. A defect in these repair mechanisms leads to a high rate of genetic mutations, significantly raising the risk for polyps and various cancers, including endometrial, ovarian, and stomach cancers. Men also tend to have higher rates of polyps than women, and women are exclusively at risk for uterine or cervical polyps.
Lifestyle and Environmental Triggers
External factors related to diet, habits, and chronic conditions interact with genetic predispositions to trigger polyp growth. Chronic irritation and inflammation are major environmental stimuli that cause cells to multiply more rapidly as the body attempts to repair damaged tissue. This increased cell turnover creates more chances for genetic errors to occur, tipping the balance toward polyp formation.
In the colon, dietary choices exert a strong influence. A diet high in red and processed meats and low in fiber is associated with an elevated risk because processed meats contain carcinogenic compounds, and low fiber slows transit time. Conversely, a diet rich in fruits, vegetables, and whole grains may help protect against polyps by promoting regular bowel movements and reducing inflammation.
Lifestyle habits such as smoking and excessive alcohol consumption are also linked to increased polyp risk, and obesity is a contributing factor. For polyps in other areas of the body, chronic inflammation remains central. For example, nasal polyps frequently develop due to chronic sinusitis or allergies that cause persistent irritation of the nasal lining. Similarly, the bacterium Helicobacter pylori (H. pylori) can cause chronic inflammation in the stomach, leading to the development of certain stomach polyps.