According to the World Health Organization, colorectal cancer is one of the most common cancers and the second leading cause of cancer deaths in the world. This slow moving disease predominantly affects people over the age of 50, but it can happen to anyone of any age. While the most common cause associated with colorectal cancer is polyps, there is a lesser-known but equally important type of growth called a sessile serrated adenoma (SSA). These flat, subtle lesions in the colon can be easily missed during routine screenings, yet they pose a significant risk for developing into colorectal cancer.1

Overview of Colorectal Cancer

Colorectal cancer, a term that encompasses both colon cancer and rectal cancer, is a type of cancer that typically develops slowly, over many years. In most cases, the cancer starts as a small growth on the inner lining of the colon or rectum called a polyp; in fact, it can be said that while not all polyps become cancerous, the majority of cases of colorectal cancer begin as polyps. Over time, these abnormal growths grow into the wall of the colon and can eventually travel to other parts of the body via the bloodstream.

Colorectal polyps can develop anywhere in the mucosa lining the large intestine, though they are more likely to show up in the ascending colon (also known as the proximal colon or right colon), the sigmoid colon, or the rectum. There are also several different types of polyps:

  • Adenomatous: Tubular adenomas are the most common type of adenomatous polyp, and they are typically small and mushroom-shaped. Villous adenomas are less common but usually larger and more likely to become cancerous. Tubulovillous adenomas combine features of both tubular and villous types.
  • Serrated: Serrated polyps are known for their distinctive shape, and some versions are considered low risk for becoming cancerous. Traditional serrated adenomas (TSA) are a rarer type that nevertheless comes with increased risk.
  • Hamartomatous: These benign overgrowths are also rare and are usually seen in children.
  • Inflammatory: This type is often associated with inflammatory bowel diseases like Crohn's disease or ulcerative colitis. They are typically not precancerous but may indicate underlying inflammation.

The development and progression of colorectal cancer is a complex process that is believed to involve both genetic and environmental factors. Under normal circumstances, the APC (adenomatous polyposis coli) gene plays an important role in suppressing the formation of tumors and regulating cell growth. When this gene becomes mutated, however, the ability to suppress cell growth is inhibited and polyps or other lesions and abnormalities can begin to form. Mutations to this gene (cytologic dysplasia) can be inherited from a parent or can occur without an apparent cause.

The genetic component of colorectal cancer is of course fixed and can’t really be mitigated, but there are also a number of environmental factors that can be adjusted for. Food choices, for instance, are a significant factor in the United States given the propensity of the American diet to include ultra-processed foods as well as red and processed meats; these foods have long been associated with increased risk of numerous poor health outcomes, including colorectal cancer. Lifestyle choices like smoking and excessive alcohol consumption are also significant risk factors, as is living a sedentary lifestyle.

What Are Sessile Serrated Adenomas?

As noted above, most cases of colorectal cancer begin as polyps of the colon, but not all polyps are the same. One of the most common subtypes is hyperplastic polyps, but these are typically benign and often go unnoticed for a person’s entire life. Sessile serrated adenomas, on the other hand, are known to be precursors of colorectal cancer. Unlike other types though, serrated polyps are harder to detect during a colonoscopy because of their size and shape.2

Serrated lesions are so named because of the sawtooth-like appearance that is visible when the crypt epithelium is viewed under a microscope. They are also fairly flat (sessile), which is one of the main reasons they can be missed during an examination. The serrated pathway is distinct from the adenocarcinoma pathway of other precancerous polyps; whereas most incidences of colorectal cancer are associated with the APC gene, SSAs are thought to begin with mutations to the BRAF gene, another protein connected to cell growth.

The prevalence of SSAs is estimated to be about 10% of all colorectal polyps, though this figure may be underestimated due to historical challenges in detection. They are more common in women and tend to occur at a slightly younger age compared to traditional adenomas. This difficulty in detection of SSAs is part of what has brought new attention to this pathway in colonoscopy screening programs. It has led to the use of more advanced imaging techniques in an attempt to catch this type more quickly.

How Are SSAs Diagnosed?

Sessile serrated adenomas are mainly diagnosed through visual inspection during a colonoscopy, a kind of endoscopy procedure that involves a long flexible tube with a camera mounted on the end. During the procedure, the endoscopist will examine the wall of the colon to look for lesions and other abnormalities. The location of a polyp can also be an important indicator, because most SSAs are found in the ascending colon or cecum, the first section of the large intestine.

Once a suspicious lesion has been identified, a biopsy is taken for a histologic examination under a microscope. The biopsy can reveal, for instance, if the polyp has the characteristic sawtooth shape that indicates a serrated lesion. Doctors can also make determinations about the extent of the problem by evaluating other aspects like the growth pattern and size. In some cases, molecular tests may also be performed to identify specific genetic mutations associated with SSAs, such as BRAF mutations. The diagnostic process also involves differentiating SSAs from other types of polyps, particularly hyperplastic polyps that can appear similar but have different potential for malignancy.

Treatment Options

If and when a serrated adenoma is detected, the main treatment is complete removal through a procedure called a polypectomy. This resection procedure is typically done during a colonoscopy with tools that are mounted on the end next to the camera. For smaller SSAs, this can be done with a wire loop, but larger or more complex SSAs require more advanced procedures like endoscopic mucosal resection (EMR). In severe cases, a portion of the colon may actually need to be removed.

After resection, the tissue is examined to confirm complete removal and to check for dysplasia or early signs of cancer. These results will then guide much of the follow-up treatment; follow-up procedures are also more common than with conventional adenomas because they can become cancerous more quickly. This means that patients with a diagnosed SSA will likely have to be checked more often because of the increased risk of new polyps. Careful monitoring becomes a key element of preventing further incidence.3

Contact Cary Gastroenterology

Colorectal cancer remains a risk for many Americans, but it is a risk that can be significantly mitigated through lifestyle choices. But since symptoms of colorectal cancer generally only arise late into the progression, it’s critically important for especially those at higher risk to take preventative measures. For most people, this means getting a screening colonoscopy at regular intervals once reaching the age of 45.

At Cary Gastro, we are dedicated to providing excellent digestive healthcare for our patients, and our team of board-certified gastroenterologists is passionate about providing peace of mind and good quality of life. If you are 45 or older and have yet to get screened for colorectal cancer, it may be the right time to get checked out. For information about screenings, colonoscopy, prep, or any other issue, please contact us to request an appointment.

1https://www.who.int/news-room/fact-sheets/detail/colorectal-cancer
2https://www.gastroendonews.com/Endoscopy-Suite/Article/06-23/Sessile-Serrated-Polyps-finding-management/70523
3https://www.gastrojournal.org/article/S0016-5085(17)35865-1/fulltext