What is Colon Cancer?
Colorectal cancer is the third most common type of cancer and a leading cause of death due to cancer in the United States for both men and women. Globally, it’s the third most common cancer, with only lung cancer having a higher mortality rate. In recent years, the number of cases has been decreasing in Western countries, thanks mainly to regular screenings via colonoscopy. However, more young adults are being diagnosed with this disease.
Most cases of colon cancer develop sporadically, but about 5 percent are caused by inherited genetic mutations, primarily linked to Lynch syndrome and familial adenomatous polyposis (FAP). The process from normal colon tissue to invasive cancer usually takes several years and typically involves a sequence of genetic mutations, the formation of benign growths known as adenomas, and then the development of cancer. However, some cancers may develop through different processes, such as those involving DNA mismatch repair and the BRAF gene.
Doctors recommend regular screening for colon cancer using various methods. Different medical organizations may have different recommendations for when to start screening and how often to get checked. To confirm a diagnosis of colon cancer, a tissue sample is usually taken during a colonoscopy. All newly diagnosed cases should be checked for common genetic mutations, and a complete colonoscopy and baseline carcinogenic test should be performed. Most patients with invasive cancer will also need a CT scan of the chest and abdomen.
Surgery is typically the first line of treatment for early-stage colon cancer that is still localized. The most important factor in determining the prognosis is the pathological stage of the cancer. This stage also determines whether further treatment is necessary, which might involve chemotherapy, immunotherapy, or, in rare cases, radiation. After treatment, regular monitoring is vital to detect any spread of the disease or local recurrence, which can often be treated with a combination of therapies. Palliative care, aimed at improving the quality of life and survival rate, is reserved for cases where cancer cannot be surgically removed, or has spread widely throughout the body.
What Causes Colon Cancer?
About 70% of colon cancer cases happen randomly and aren’t tied to any known genetic mutations. Conditions with identified inherited genetic changes, like HNPCC and FAP, make up 3% to 5% of cases. Around 20% to 25% of patients with colon cancer have a strong family history of the disease, but no detected inherited mutation.
There are several risk factors that increase the chances of developing colon cancer:
- Age: Most people diagnosed with spontaneous colon cancer are over 65.
- Family history: Having a relative with colon cancer increases your risk.
- Inherited genetic conditions: Specific inherited conditions such as HNPCC, FAP, and Peutz-Jegher polyposis increase the likelihood of getting colon cancer.
- Adenomas detected during colonoscopy: The presence of certain types of polyps significantly increases cancer risk.
- History of inflammatory bowel disease (IBD): People with Ulcerative colitis have a yearly risk of developing colon cancer that increases over time. Crohn’s disease may also raise the risk if it affects specific regions of the colon.
- Environmental and lifestyle factors: Certain factors like drinking alcohol, smoking, being obese, eating lots of processed red meat, insulin resistance, previous radiation exposure, and suppression of the immune system can increase colon cancer risk.
However, some factors have been found to potentially protect against colon cancer:
- Regular physical activity
- Eating a diet rich in fruits, vegetables, fiber, resistant starch, and fish
- Taking supplements with folate, folic acid, pyridoxine, calcium, vitamin D, and magnesium
- Eating garlic
- Drinking coffee
- Taking certain medications, including aspirin, other nonsteroidal anti-inflammatory drugs, hormone replacement therapy in postmenopausal women, statins, bisphosphonates, and angiotensin inhibitors.
Note that the evidence supporting these protective factors varies in quality.
Risk Factors and Frequency for Colon Cancer
Colorectal cancer is known as the third most common type of cancer in the United States. The Surveillance, Epidemiology, and End Results (SEER) database estimated that over 153,000 new cases were diagnosed in 2023, making up 7.8% of all new cancer diagnoses. Among these, around 70% were found in the colon, while the remaning were tumors in the rectum.
Men are more prone to this condition, making up 53% of the cases and generally getting diagnosed at a younger age than women – approximately 68 years versus 72 years respectively. Despite an overall decrease in cases, the pace of decrease has slowed down lately. Notably, an increasing number of cases are found in individuals under the age of 55. There is also an observed rise in right-sided colon cancers and rectal cancers.
- Colorectal cancer is the third most diagnosed cancer in the United States.
- Over 153,000 new cases were identified in 2023, making up 7.8% of all new cancer diagnoses.
- About 70% of these cases were tumors in the colon, while the rest were in the rectum.
- Men are more susceptible to this condition, usually getting diagnosed at a younger age than women (on average, 68 years vs. 72 years).
- Although there’s a decreasing trend in the number of cases, the rate of decrease has slowed recently.
- An increasing number of diagnoses are found in individuals younger than 55.
- There’s an increase in the proportion of right-sided colon cancers and rectal cancers.
Race and socioeconomic status play a significant role in both the number of cases and how the disease progresses. Alaskan natives and African Americans have been noted to have the highest rates. Globally, the rates of colorectal cancer can vary considerably based on the population, race, and socioeconomic status, with the highest rates found in more developed countries.
Signs and Symptoms of Colon Cancer
Colon cancer is often detected during routine screenings before any symptoms appear. However, if symptoms do manifest, they’ll vary depending on the size and location of the tumor. These symptoms can trigger colonoscopy tests and include rectal bleeding, belly pain, and anemia. Sometimes, tumors on the right side of the colon can lead to anemia, while those on the left side can disrupt bowel movements. In some cases, people may experience severe conditions like obstructions, perforations, or excessive bleeding due to the tumor. Advanced colon cancer may show different symptoms based on the affected organ.
- Rectal bleeding
- Abdominal pain
- Anemia
- Disrupted bowel movements
- Obstructions
- Perforations
- Excessive bleeding
If colon cancer is suspected, a detailed physical examination is performed, focusing on signs of the disease spreading. This could include a thorough examination of the abdomen for any discomfort, detectable lumps, hernias, unusual scars, and enlarged organs. A rectal exam is a crucial part of this process, helping medical professionals check for signs of cancer and assess sphincter muscle control and bowel continence.
Testing for Colon Cancer
The first step in testing for colon cancer often involves a barium enema or a type of CT scan specially designed to examine the colon. However, for a definitive diagnosis, a colonoscopy, a test where a long flexible tube is inserted into the rectum to view the entire colon, is needed. Colonoscopies are generally accurate, catching about 94.7% of issues when carried out by an experienced professional and with a well-prepared bowel. However, it is possible to miss between 2% to 6% of problems, particularly on the right side of the colon or with growths that lie flat or are attached by a broad base.
During the colonoscopy, the doctor will take several samples of the suspicious area and mark the surrounding colon for easy identification during any further procedure. Routine blood tests, including complete blood counts, iron levels, basic metabolic rate, liver function, and blood clotting tests should also be done. This is because colon cancer can sometimes lead to iron deficiency anemia due to ongoing bleeding from the tumor.
The most commonly used indicator for colon cancer is a biomarker called CEA, which should be measured as a starting point. If CEA levels are high, it often indicates a worse prognosis, and checking these levels after treatment can help detect if the disease comes back.
The National Comprehensive Cancer Network (NCCN) recommends everyone diagnosed with colon cancer undergo testing for MMR/MSI status. This status affects approximately 15% to 20% of all colon cancer cases without a known genetic link. Additionally, they recommend mutation testing for genes like KRAS, NRAS, HER2, and BRAF in patients with colon cancer that cannot be surgically removed. Chest, abdomen, and pelvic CT scans are suggested for all patients diagnosed with colon cancer. If a patient is allergic to the contrast dye used in CT scans or if liver metastasis is suspected, MRI could be used. Positron Emission Tomography-CT scans, however, are not regularly recommended.
Treatment Options for Colon Cancer
Surgery to remove the affected part of the colon is the normal treatment for colon cancer that hasn’t spread too widely. The specific surgical methods and how many surrounding lymph nodes are removed will depend on how advanced and where the cancer is located. Some more severe colon cancers may also be treated with additional chemotherapy after surgery. When the cancer has spread to other parts of the body, treatment will involve medications that work throughout the body. Radiation therapy isn’t often used in colon cancer treatment. In more advanced cases, certain surgical procedures can be used to alleviate symptoms and improve comfort for the patient.
What else can Colon Cancer be?
When a doctor is trying to diagnose colon cancer, it’s important to remember there are other conditions that can mimic its symptoms. These include:
- Arteriovenous malformation: This might lead to bleeding from the rectum.
- Carcinoid tumors: These are unusual growths that may originate from specific cells within the lining of the colon. They can cause belly aches, changes in bowel movements, rectal bleeding, or symptoms similar to bowel obstruction. But sometimes, these tumors don’t cause any symptoms and are found during a colonoscopy.
- Crohn’s disease: This can cause inflammation and narrowing of the colon that might look like cancer.
- Gastrointestinal lymphoma: This can form a blockage or a large mass in the bowel.
- Ischemic bowel: This can cause abdominal pain and blood in the stool.
- Ileus: This is a condition where the bowels stop working and might cause symptoms similar to those seen in advanced colon cancer.
- Small intestine carcinomas: These can present with nonspecific symptoms, like abdominal pain and bowel obstruction, similar to colon cancer.
- Small intestine diverticulosis: This can cause belly pain and bleeding, and is accompanied by changes in bowel habits.
- Ulcerative colitis: The symptoms of this condition can overlap with those of cancer.
Careful assessment and testing by a doctor can help differentiate colon cancer from these other conditions.
Surgical Treatment of Colon Cancer
Surgery is an essential part of colon cancer treatment, helping both in diagnosis and treatment of the disease. Surgeons aim to remove the entire tumor while trying to keep as much of the bowel’s normal function as possible and minimizing the risk of complications. In some cases, emergency procedures may be needed to relieve a blockage before the main surgery can take place.
One of the surgical methods used is endoscopic resection. This involves using a thin, flexible tube called a colonoscopy to remove cancerous growths, like polyps. This can be done in several ways, including simply removing the polyp (polypectomy), trimming off layers of cancer cells (endoscopic mucosal resection), or taking out the whole layer of cells where the cancer started (endoscopic submucosal dissection). Depending on the cancer’s characteristics, further operations may be needed. Some potential side effects, though rare, include perforation or bleeding. Afterwards, it’s recommended that patients have regular check-ups.
The key goal of surgical resection is the total removal of the cancerous part of the colon, along with clearance of surrounding lymph nodes. The exact surgical method used depends on the cancer’s location within the colon. Whether done through traditional, minimally invasive (laparoscopic), or robotic-assisted surgery, the same basic principles apply.
For cancers located in different parts of the colon, specific surgeries are performed. Sigmoid colon cancers (in the lower part of the colon) are treated with a sigmoid colectomy, which involves removing part of the colon. Cancers in the left colon and area near the spleen (splenic flexure) are dealt with through a left colectomy. Tumors in the middle section of the colon (transverse colon) are typically removed via a transverse colectomy. Right-side colon and hepatic flexure tumors are managed with a right colectomy.
In emergency cases where there’s a risk of obstruction, heavy bleeding, or twisting of the intestine (volvulus), immediate surgical intervention may be needed. If possible, the primary cancer should be removed during this operation. However, to avoid complications, it may be necessary to create an alternate path for waste to leave the body (a stoma) instead of reconnecting the bowel. Another option in these situations is to place a temporary stent to relieve the obstruction and later conduct a planned colon resection.
Lastly, it’s worth noting that different types of surgery might be necessary for patients with inherited conditions that result in many polyps in the colon. These cases are discussed in detail in social chapters.
What to expect with Colon Cancer
The outlook for colon cancer patients largely depends on the stage of the cancer at diagnosis. The most crucial factor determining the outlook is the pathological stage, as indicated by SEER data. Specifically, the five-year survival rate is as follows: 74% for stage I, 66% for stage IIA, 58% for stage IIB, 37% for stage IIC, 73% for stage IIIA, 46% for stage IIIB, 28% for stage IIIC, and only 5% for stage IV.
When you look at it from a different angle, the five-year survival rate is 90% for localized disease, 73% for regional disease, and 13% for distant disease. The average five-year survival rate for all cases is 63%.
Moreover, certain factors related to the patient can also affect the outlook. These include the patient’s age, other existing medical conditions, and specific aspects related to the tumor itself.
Possible Complications When Diagnosed with Colon Cancer
Colon cancer can lead to a variety of complications. These can be related to the primary tumor itself or due to the spread of the cancer to other parts of the body. When related to the primary tumor, complications can include bleeding, blockages, tearing, and the development of abnormal connections to surrounding organs. When the disease spreads, symptoms vary depending on where the cancer has spread to. There can also be complications related to surgery such as bleeding, infections at the surgical site or within organ spaces, leakages at stitched connections, injury to nearby structures like the tubes connected to the kidneys and the first part of the small intestine, and complications over time like incisional hernias. The side effects of chemotherapy are a different topic and are not covered here.
Common complications of colon cancer and its surgery are:
- Bleeding
- Blockage
- Tearing
- Abnormal connections to surrounding organs
- Symptoms based on where the cancer has spread
- Bleeding and Infections linked to surgery
- Leakages at stitched connections
- Injury to nearby parts like kidney-connected tubes and small intestine parts
- Long-term complications like hernias
Preventing Colon Cancer
Colon cancer ranks as the third most common cancer among men and women. This type of cancer usually originates from polyps, or small clumps of cells in the colon, and develops over several years. A medical procedure known as a colonoscopy is effective in finding these polyps and screening for colon cancer. Doctors generally recommend starting these check-ups at age 45 for most people who are at a normal risk.
However, for those who have a higher chance of getting colon cancer, such as those having genetic conditions like FAP or HNPCC or a strong family history of colon cancer, it’s advised to start these screenings earlier. Treatment for colon cancer usually involves surgery, especially for cases that are localized and haven’t spread to other parts of the body. In situations where the cancer has deeply invaded the tumor or affected the lymph nodes, chemotherapy after surgery might be necessary.
For cancer that has spread to distant parts of the body, known as metastatic cancer, chemotherapy is the main form of treatment, with surgery used mainly to relieve symptoms or improve quality of life. In some instances, if the cancer has spread only to specific areas like the liver, peritoneum, or lungs, surgical management might be possible and is often linked with better outcomes. The five-year survival rate for patients diagnosed with colon cancer is 63%, and this figure continues to improve with advancements in medical treatments and care.