Colorectal cancer is a type of cancer that develops in the large intestines, which is often called the colon. This is the final section of your digestive tract before the rectum and anus.
The disease starts out as clumps or clusters of cells that line the colon. These are called polyps. Over time, some polyps will resolve themselves. However, others will continue to grow and may turn into cancer.
Colon cancer is the second deadliest cancer that can affect both men and women. It's also one of the easiest to screen for and, when caught early, has a high survival rate. For every ten people diagnosed early, nine are still living after five years¹.
Colorectal cancer screening involves finding precancerous polyps. If these polyps are removed, they won't become cancerous.
There has long been an understanding that colon cancer was due to abnormal cell growth from sporadic DNA mutations². While this is often true, there has been some controversy over whether anal sex can also cause colon cancer.
After all, over 90% of anal cancer cases are due to previous human papillomavirus (HPV) infection, which can occur after sexual contact³. HPV is the most common sexually transmitted infection.
Can anal sex cause colon cancer? According to some researchers, there may be an association between the two.
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There are 45,300 new HPV-related cancer diagnoses every year, and 35,900 of those cases are caused by the virus³. HPV can infect both males and females. It's the most common sexually transmitted disease that almost all sexually active people come into contact with at some point⁴.
About 37 new colon cancer cases are reported out of every 100,000 Americans each year, and 13 of those cases die from the disease annually⁵.
In a study of 1,436 cases of colorectal cancer, 31.9% were HPV-positive⁶. In another study of 55 patients with colon cancer, 51% had HPV DNA present in their samples⁷.
There are over 200 different types of HPV, and most of them do not cause cancer. The types that do the most harm are linked to cancers of the cervix, oropharynx (back of the mouth), vagina, vulva, penis, and anus. This is because these areas are involved in sexual activity, and if the body cannot fight off the virus, it can cause the tissue to change over time. Most of these cancers are squamous cell carcinomas, affecting the cell walls lining the area.
There is some debate about whether colon cancers are caused by anal sex. However, there is quantitative evidence that HPV is present in many cases. This means that it cannot be ruled out. It also means that while colon cancer is associated with HPV, anal sex may not be the direct cause, like it is in 90% of anal cancer cases³.
Colon cancer is usually caused by a mutation in the DNA of the cells that line the colon and rectum. Doctors do not know the exact cause that triggers the mutation. However, some factors are present in many cases of colon cancer, including anal sex practices and HPV transmission.
Colon cancer is a disease that affects men and women, but more cases are in men. Some general causes and risk factors include:
Age – The older you are, the higher the risk. Most people diagnosed are over 50 years old.
Race – African Americans are at a higher risk of developing colon cancer.
Polyps – A medical history of intestinal, colon, or rectal polyps increases the risk of colon cancers.
Hereditary – If you have a family history of colorectal cancer, you will be at a higher risk yourself.
Diet – High-fat, low-fiber diets have been associated with bowel inflammation and colon cancer.
Lifestyle – Obesity, smoking, alcohol, and a sedentary lifestyle have all been linked to colon cancer.
Because we cannot rule out whether anal sex causes colon cancer, the first step in prevention should be safer sex practices. This advice goes to anyone who is sexually active, as this is how HPV is spread.
Vaccination against HPV is available for people aged 11 – 45 with a series of Gardasil 9 injections. For the best protection, a person should be vaccinated before becoming sexually active.
Most healthcare professionals believe that vaccination at around 9-12 years old offers the best protection against HPV-related cancers⁴. If you are no longer a teenager, your doctor may recommend the shot if you are under 45 and at high risk. However, the vaccine will not fight HPV if you’re already infected.
If you've noticed any symptoms or changes in your bowels, you should see your doctor. The number one sign to look out for is bleeding of any kind when you have a bowel movement. This can be a sign that you have polyps or tears in your gastrointestinal tract. It also warrants screening for colon cancer.
Most doctors recommend regular colon cancer screening after age 50 for people with an average risk of the disease. People that are at higher risk should talk with their doctors about earlier screening.
It is important to remember that this type of cancer is highly treatable when caught early. There are even at-home tests available.
If you have any concerns about your risk of developing colon cancer, you should talk to your doctor. You should be honest with them about your sexual history, including anal sex practices and any symptoms you have. This will help your doctor gauge what your risk is and suggest ways that you can protect yourself.
There is evidence that colon cancer and anal sex are associated, but more research is needed to determine the link. Regular screening is the most effective way to find cancer and, when caught early, prevent the disease from spreading.
If you're diagnosed with colon cancer, your doctor can go over treatment options with you, including various colon cancer research and clinical trials that you may be a match for right now.
What is the Difference Between Anal Cancer and Colon Cancer? | Roswell Park
HPV and Cancer | National Cancer Institute