Colorectal cancer, commonly referred to as colon cancer, is a malignancy where abnormal cell growth begins in the large intestine. A family history of this disease is a recognized factor that increases an individual’s personal risk. This familial connection, including a history on the maternal side, prompts many to consider the likelihood of cancer being passed down through generations. Understanding this risk requires distinguishing between a general family pattern and a specific inherited genetic condition.
Familial Risk vs. Inherited Syndromes
The connection between family history and colon cancer is divided into two main categories of risk. Familial risk is the more common scenario, involving an increased chance of developing the disease when a close relative, such as a mother, father, or sibling, has been diagnosed. This elevated risk often results from a combination of shared lifestyle factors, common environmental exposures, and the cumulative effect of multiple low-risk genes.
Hereditary cancer syndromes, in contrast, represent a smaller but higher-risk percentage of cases, accounting for five to ten percent of all colorectal cancers. These syndromes are caused by a specific, high-penetrance mutation in a single gene passed directly from a parent to a child. When a high-risk mutation is present, the pattern of inheritance is autosomal dominant.
This means a person needs only one copy of the altered gene to inherit the predisposition. The risk of transmission is the same regardless of whether the affected parent is the mother or the father. Therefore, the cancer predisposition is not distinctly maternal or paternal; it has an equal fifty percent chance of being passed on to any child. A confirmed inherited syndrome carries a much higher lifetime risk compared to general familial clustering.
Key Hereditary Colon Cancer Syndromes
The two most frequently encountered high-risk syndromes are Lynch Syndrome and Familial Adenomatous Polyposis (FAP). Lynch Syndrome, also known as Hereditary Non-Polyposis Colorectal Cancer, is the more common, resulting from inherited defects in DNA mismatch repair (MMR) genes. These genes (MLH1, MSH2, MSH6, and PMS2) normally fix errors that occur when DNA is copied, and their malfunction allows mutations to accumulate rapidly.
Individuals with Lynch Syndrome have a significantly increased lifetime risk of colorectal cancer, ranging from forty to eighty percent, often developing at a younger age. The syndrome is also associated with an elevated risk for several other malignancies, most notably endometrial (uterine) cancer, ovarian, stomach, and urinary tract cancers. The specific cancer risks vary depending on which of the MMR genes is mutated.
Familial Adenomatous Polyposis (FAP) is a less common but extremely high-risk syndrome caused by a mutation in the APC gene. This mutation results in the growth of hundreds to thousands of adenomatous polyps throughout the colon and rectum, often beginning in childhood. Without preventative intervention, a person with FAP has a nearly one hundred percent chance of developing colorectal cancer, typically diagnosed around age forty. FAP also increases the risk for polyps and cancer in other parts of the gastrointestinal tract, particularly the duodenum.
Genetic Testing and Counseling
Identifying a hereditary risk begins with a detailed review of family history, noting the number of affected relatives and their ages at diagnosis. Genetic testing confirms the presence of a specific, high-risk gene mutation. Testing is recommended if a person has a first-degree relative diagnosed with colorectal cancer before age fifty or if the family history includes multiple relatives with cancers associated with Lynch Syndrome.
The first step often involves a referral to a genetic counselor, who assesses the family pedigree and determines the likelihood of a hereditary condition. Genetic counselors explain the complex implications of a positive or negative test result and assist with informed decision-making. Ideally, testing is performed on the family member who has already had cancer, as finding a mutation in an affected individual makes it easier to offer targeted testing to other relatives.
A positive test result confirms the hereditary syndrome, allowing for personalized cancer prevention strategies. Conversely, a negative result for a known family mutation can provide reassurance, though the individual may still remain at an increased familial risk due to shared non-syndromic factors. The test results provide clarity that guides medical management for the individual and their relatives.
Tailored Screening for High-Risk Individuals
Once a high-risk profile is established, screening protocols must be significantly accelerated compared to the general population. For individuals who have a first-degree relative with colon cancer but no identified genetic syndrome, screening typically begins earlier. Guidelines suggest starting colonoscopy at age forty, or ten years younger than the age of the relative’s diagnosis, whichever comes first, with surveillance repeated every five years.
For those diagnosed with Lynch Syndrome, the aggressive nature of the disease necessitates more frequent surveillance. Colonoscopy is recommended to begin between ages twenty to twenty-five, performed every one to two years. Women with Lynch Syndrome also require surveillance for endometrial cancer, often involving transvaginal ultrasound or endometrial biopsies.
Individuals with Familial Adenomatous Polyposis face the most intensive screening schedule due to the near-certainty of cancer development. Screening with flexible sigmoidoscopy or colonoscopy often starts as early as age ten to twelve, performed annually to detect and remove polyps before they become malignant. Surveillance for polyps in the stomach and small intestine, typically with an upper endoscopy, is a regular part of managing FAP.