Colorectal Cancer: Symptoms, Causes & Treatment Guide

What Is Colorectal Cancer?

Colorectal cancer is a malignant tumor that develops in the colon (large intestine) or rectum. It typically begins as small, noncancerous polyps that can transform into cancer over 10-15 years. As the third most common cancer globally, colorectal cancer affects approximately 1.9 million people annually, but early detection through screening dramatically improves outcomes.

The colon and rectum form the large intestine, the final part of the digestive system. The colon is approximately 5 feet long and absorbs water and nutrients from digested food, while the rectum is the last 6 inches of the large intestine where stool is stored before elimination. Cancer can develop in any part of this system, though the specific location influences both symptoms and treatment approaches.

Colorectal cancer typically develops from abnormal growths called polyps that form on the inner lining of the colon or rectum. While most polyps are benign, certain types, particularly adenomatous polyps (adenomas), can become cancerous over time. This slow progression from polyp to cancer, usually spanning 10-15 years, provides a crucial window for detection and prevention through regular screening colonoscopy.

The disease affects both men and women, though men have a slightly higher risk. While traditionally considered a disease of older adults, recent data shows increasing rates among younger people under 50, prompting many medical organizations to lower the recommended screening age from 50 to 45 years. Understanding the risk factors, recognizing early symptoms, and adhering to screening guidelines are essential for prevention and early detection.

Types of Colorectal Cancer

The vast majority of colorectal cancers (over 95%) are adenocarcinomas, which develop from the glandular cells that produce mucus to lubricate the colon and rectum. However, several other, rarer types exist:

• Adenocarcinoma: The most common type, arising from gland cells lining the intestine
• Carcinoid tumors: Slow-growing tumors originating from hormone-producing cells
• Gastrointestinal stromal tumors (GISTs): Develop from specialized cells in the intestinal wall
• Lymphomas: Cancers of the immune system that can start in the colon or rectum
• Sarcomas: Rare cancers arising from blood vessels, muscle, or connective tissue

How Colorectal Cancer Develops

Colorectal cancer develops through a well-understood sequence of genetic mutations that transform normal intestinal cells into cancerous ones. This process, known as the adenoma-carcinoma sequence, typically takes 10-15 years and involves multiple genetic changes.

Initially, mutations in genes like APC (adenomatous polyposis coli) cause cells to grow and divide more rapidly than normal, forming a polyp. Additional mutations in genes such as KRAS and TP53 progressively accumulate, leading to larger polyps with increasingly abnormal cells. Eventually, cells acquire the ability to invade surrounding tissues and spread to other parts of the body, characteristics that define cancer.

This extended timeline from normal cell to cancer provides an extraordinary opportunity for prevention. Colonoscopy allows physicians to identify and remove polyps before they become cancerous, effectively breaking the chain of cancer development. This is why regular screening has been so successful in reducing colorectal cancer incidence and mortality.

What Are the Symptoms of Colorectal Cancer?

The most common symptoms of colorectal cancer include changes in bowel habits (persistent diarrhea, constipation, or narrower stools), blood in the stool (bright red or very dark), persistent abdominal discomfort, a feeling that the bowel doesn't empty completely, weakness or fatigue from anemia, and unexplained weight loss. Early-stage colorectal cancer often has no symptoms, making screening crucial.

Colorectal cancer symptoms vary depending on the tumor's location, size, and stage. Cancers in the right colon (ascending colon) often grow large before causing symptoms because this area has a wider diameter and liquid stool. These tumors frequently cause iron-deficiency anemia due to slow, chronic blood loss, leading to fatigue, weakness, and shortness of breath.

Left-sided colon cancers and rectal cancers are more likely to cause obstructive symptoms earlier because the colon narrows as it approaches the rectum and stool becomes more formed. Patients may notice changes in bowel habits, narrower stools, or visible blood in stool. Rectal cancers specifically may cause a sensation of incomplete evacuation, rectal pain, or mucus discharge.

It's important to recognize that many people with early colorectal cancer experience no symptoms at all. By the time symptoms appear, the cancer may have grown considerably or even spread to other organs. This underscores why screening is so critical: it can detect cancer or precancerous polyps before symptoms develop.

Common Warning Signs

While symptoms can vary, certain warning signs should prompt medical evaluation. Any persistent change lasting more than a few weeks warrants attention:

• Blood in stool: Bright red blood (more common with rectal cancer) or dark, tarry stools (indicating bleeding higher in the colon)
• Changes in bowel habits: Persistent diarrhea, constipation, or alternating between the two
• Narrower stools: Pencil-thin stools that persist for more than a few days
• Incomplete evacuation: Feeling that the bowel doesn't empty completely
• Abdominal discomfort: Persistent cramps, gas, or pain
• Unexplained weight loss: Losing weight without trying
• Fatigue and weakness: Often from anemia due to chronic blood loss

Symptoms by Cancer Location

What Causes Colorectal Cancer?

Colorectal cancer develops when cells in the colon or rectum acquire genetic mutations that cause uncontrolled growth. While the exact cause isn't always identifiable, risk factors include age over 50, family history of colorectal cancer or polyps, hereditary syndromes (Lynch syndrome, FAP), inflammatory bowel disease, obesity, smoking, excessive alcohol consumption, diet high in red and processed meats, and sedentary lifestyle.

Cancer fundamentally results from accumulated genetic damage that disrupts normal cell growth and division. In colorectal cancer, this process typically unfolds over many years, with cells progressively acquiring mutations that enable increasingly abnormal behavior. While some people inherit genetic mutations that significantly increase risk, most colorectal cancers result from mutations acquired during a person's lifetime.

Environmental and lifestyle factors play a substantial role in colorectal cancer risk. Research consistently shows that diet, physical activity, body weight, smoking, and alcohol consumption all influence the likelihood of developing this disease. Importantly, many of these factors are modifiable, meaning lifestyle changes can meaningfully reduce risk.

Chronic inflammation also contributes to colorectal cancer development. Patients with inflammatory bowel diseases like ulcerative colitis and Crohn's disease have elevated risk, particularly those with extensive, long-standing disease. The persistent inflammation creates an environment where genetic damage accumulates more readily.

Risk Factors You Cannot Change

• Age: Risk increases substantially after age 50, though rates among younger people are rising
• Personal history: Previous colorectal cancer or polyps increases risk of new cancers
• Family history: First-degree relatives with colorectal cancer or advanced adenomas double to triple risk
• Hereditary syndromes: Lynch syndrome accounts for 3-5% of colorectal cancers; familial adenomatous polyposis (FAP) causes nearly 100% risk without treatment
• Inflammatory bowel disease: Ulcerative colitis and Crohn's disease increase risk, especially after 8-10 years of disease
• Type 2 diabetes: Associated with modestly increased colorectal cancer risk
• Race and ethnicity: African Americans have the highest incidence and mortality rates in the United States

Modifiable Risk Factors

Research has identified several lifestyle factors that influence colorectal cancer risk. Addressing these factors offers meaningful opportunities for prevention:

• Diet: High consumption of red meat (especially beef, pork, lamb) and processed meats (bacon, sausage, hot dogs) increases risk. High-fiber diets appear protective.
• Obesity: Excess body weight, particularly abdominal fat, increases risk by 30-60% compared to normal weight
• Physical inactivity: Sedentary lifestyle increases risk; regular exercise reduces it by 20-30%
• Smoking: Long-term smoking increases risk and is linked to larger polyps and earlier-onset disease
• Alcohol: Moderate to heavy drinking (more than 2-3 drinks daily) increases risk substantially

When Should You Get Screened for Colorectal Cancer?

Most guidelines now recommend beginning colorectal cancer screening at age 45 for average-risk individuals. Colonoscopy every 10 years is the gold standard, though other options include annual fecal immunochemical testing (FIT), stool DNA testing every 3 years, or flexible sigmoidoscopy every 5 years. People with higher risk factors should begin earlier with colonoscopy. Screening reduces colorectal cancer mortality by 68%.

Colorectal cancer screening represents one of the most effective cancer prevention strategies available. Unlike screening tests that simply detect cancer earlier, colonoscopy can actually prevent cancer by finding and removing precancerous polyps. This explains why regions with high screening rates have seen substantial declines in both colorectal cancer incidence and mortality.

The choice of screening test depends on individual preferences, risk factors, and access. Colonoscopy remains the gold standard because it allows direct visualization of the entire colon and rectum, with simultaneous removal of any polyps found. However, it requires bowel preparation, sedation, and carries small risks of complications. Stool-based tests offer convenience but require follow-up colonoscopy if positive.

Recent guideline changes lowering the recommended screening age from 50 to 45 reflect concerning trends: colorectal cancer incidence among adults younger than 50 has increased by about 2% annually since the mid-1990s. This rise in "early-onset" colorectal cancer makes it crucial for younger adults to discuss their individual risk with healthcare providers.

Screening Options Compared

When to Start Screening Earlier

Certain individuals should begin screening before age 45 or receive more frequent screening:

• Family history: Begin at age 40, or 10 years before the youngest affected first-degree relative's age at diagnosis, whichever is earlier
• Lynch syndrome: Colonoscopy every 1-2 years starting at age 20-25
• Familial adenomatous polyposis: Annual flexible sigmoidoscopy starting at age 10-12
• Inflammatory bowel disease: Surveillance colonoscopy beginning 8-10 years after diagnosis, every 1-3 years depending on extent of disease
• Personal history of polyps: Follow-up interval based on polyp number, size, and pathology (typically 3-5 years)
• Previous colorectal cancer: Colonoscopy 1 year after surgery, then based on findings

How Is Colorectal Cancer Diagnosed?

Colorectal cancer is diagnosed primarily through colonoscopy with biopsy, which allows direct visualization of the tumor and collection of tissue samples for microscopic examination. Once cancer is confirmed, staging involves CT scans of the chest, abdomen, and pelvis to determine if the cancer has spread. Additional tests may include MRI (especially for rectal cancer), PET scan, and blood tests including CEA tumor marker.

The diagnostic process typically begins when a patient presents with symptoms or has an abnormal screening test. A thorough medical history explores symptoms, duration, family history, and risk factors. Physical examination includes a digital rectal examination, which can detect masses in the lower rectum.

Colonoscopy is the definitive diagnostic procedure. During colonoscopy, a flexible tube with a camera is inserted through the rectum to examine the entire colon. Any suspicious areas can be biopsied, and polyps can be removed. The tissue samples are then examined under a microscope by a pathologist to determine if cancer is present and its characteristics.

Once colorectal cancer is diagnosed, staging determines the extent of disease, which is crucial for treatment planning. The TNM staging system evaluates three components: the size and depth of the primary tumor (T), whether cancer has spread to nearby lymph nodes (N), and whether distant metastases are present (M).

Diagnostic Tests

• Colonoscopy with biopsy: Direct visualization and tissue sampling; gold standard for diagnosis
• CT scan (chest, abdomen, pelvis): Evaluates tumor extent and checks for spread to liver, lungs, and lymph nodes
• MRI: Particularly valuable for rectal cancer to assess local invasion and guide surgical planning
• PET scan: May be used for staging advanced disease or detecting recurrence
• CEA blood test: Carcinoembryonic antigen serves as a tumor marker; elevated levels may indicate advanced disease; primarily used for monitoring treatment response and detecting recurrence
• Molecular testing: Tumor tissue is tested for specific genetic markers (MSI, KRAS, NRAS, BRAF) that guide treatment decisions

Staging and What It Means

How Is Colorectal Cancer Treated?

Colorectal cancer treatment depends on stage and location. Surgery is the primary treatment for localized disease, removing the tumor and nearby lymph nodes. Chemotherapy may be given after surgery (adjuvant) to reduce recurrence risk, or before surgery (neoadjuvant) to shrink tumors. Rectal cancer often requires radiation therapy. Advanced disease may benefit from targeted therapy or immunotherapy, particularly for tumors with specific genetic features like MSI-high status.

Treatment planning for colorectal cancer involves a multidisciplinary team including surgeons, medical oncologists, radiation oncologists, gastroenterologists, radiologists, and pathologists. This collaborative approach ensures that treatment is tailored to each patient's specific situation, considering tumor characteristics, stage, location, overall health, and personal preferences.

The approach to colon cancer and rectal cancer differs in important ways. Colon cancer is primarily treated with surgery, potentially followed by chemotherapy based on pathological staging. Rectal cancer, due to its location in the pelvis and proximity to other structures, often requires a more complex approach that may include radiation therapy and chemotherapy before surgery (neoadjuvant treatment) to shrink the tumor and improve surgical outcomes.

For advanced colorectal cancer that has spread to other organs, treatment focuses on controlling disease progression and maintaining quality of life. Modern treatments including targeted therapies and immunotherapy have significantly improved outcomes for some patients with metastatic disease. In select cases, surgical removal of metastases (particularly liver metastases) can even be curative.

Surgical Treatment

Surgery remains the cornerstone of colorectal cancer treatment for non-metastatic disease. The specific procedure depends on tumor location:

• Colectomy: Removal of the affected portion of the colon along with nearby lymph nodes. Can be performed as open surgery or minimally invasive (laparoscopic or robotic)
• Low anterior resection: For rectal cancers, removes the rectum while preserving the anal sphincter
• Abdominoperineal resection: For very low rectal cancers, removes the rectum and anus, requiring a permanent colostomy
• Local excision: For very early cancers or high-risk polyps, removal through colonoscopy or transanal approach without major surgery

Chemotherapy

Chemotherapy uses drugs to kill cancer cells or prevent them from dividing. It may be used in several settings:

• Adjuvant chemotherapy: Given after surgery for stage III (and some high-risk stage II) cancers to reduce recurrence risk. Typically 3-6 months of treatment.
• Neoadjuvant chemotherapy: Given before surgery, often combined with radiation for rectal cancer, to shrink tumors
• Palliative chemotherapy: For metastatic disease, aims to control cancer growth and extend survival

Common chemotherapy regimens include FOLFOX (5-fluorouracil, leucovorin, oxaliplatin), FOLFIRI (5-fluorouracil, leucovorin, irinotecan), and capecitabine (oral 5-fluorouracil). Side effects vary but may include fatigue, nausea, diarrhea, peripheral neuropathy (particularly with oxaliplatin), and increased infection risk.

Radiation Therapy

Radiation therapy uses high-energy beams to destroy cancer cells. It is primarily used for rectal cancer, where it can shrink tumors before surgery and reduce local recurrence. Radiation is less commonly used for colon cancer except in specific situations such as tumor adhesion to other structures.

Targeted Therapy and Immunotherapy

These newer treatments target specific characteristics of cancer cells:

• Anti-VEGF therapy (bevacizumab, ramucirumab): Blocks blood vessel growth that tumors need to survive
• Anti-EGFR therapy (cetuximab, panitumumab): Blocks the epidermal growth factor receptor; only effective in tumors without KRAS/NRAS mutations
• Immunotherapy (pembrolizumab, nivolumab): Highly effective for tumors with microsatellite instability-high (MSI-H) or mismatch repair deficiency (dMMR), found in about 15% of colorectal cancers

How Can You Prevent Colorectal Cancer?

Colorectal cancer prevention involves both screening (to detect and remove precancerous polyps) and lifestyle modifications. Key prevention strategies include regular screening starting at age 45, maintaining a healthy weight, exercising regularly, eating a high-fiber diet rich in fruits and vegetables, limiting red and processed meat, avoiding excessive alcohol, and not smoking. These lifestyle changes can reduce colorectal cancer risk by 50-60%.

Colorectal cancer offers exceptional opportunities for prevention compared to most other cancers. This is because the disease typically develops slowly from precancerous polyps, providing a window for detection and removal before cancer ever develops. Additionally, research has clearly identified modifiable risk factors that influence disease development.

Screening is the most powerful prevention tool. Colonoscopy doesn't just detect cancer early; it actually prevents cancer by finding and removing precancerous polyps. Studies consistently show that regular colonoscopy reduces colorectal cancer incidence by 40% and mortality by 68%. Even stool-based tests, which are less effective at detecting polyps, significantly reduce cancer deaths when used regularly.

Lifestyle modifications complement screening by addressing underlying risk factors. The evidence for diet, exercise, and weight management is compelling. Population studies consistently show that societies with traditional diets high in fiber and low in red meat have lower colorectal cancer rates, while Westernized diets are associated with higher rates.

Evidence-Based Prevention Strategies

• Get screened: Follow recommended screening guidelines starting at age 45 (or earlier if you have risk factors)
• Maintain healthy weight: Obesity increases risk by 30-60%; even modest weight loss helps
• Exercise regularly: Aim for 150 minutes of moderate activity weekly; reduces risk by 20-30%
• Eat high-fiber diet: Emphasize whole grains, fruits, vegetables, and legumes
• Limit red meat: Reduce consumption of beef, pork, lamb; limit to 12-18 ounces weekly
• Avoid processed meats: Bacon, hot dogs, sausages are classified as carcinogenic
• Limit alcohol: If you drink, limit to 1 drink daily for women, 2 for men
• Don't smoke: Smoking increases colorectal cancer risk and is linked to larger polyps
• Consider aspirin: Daily low-dose aspirin may reduce risk, but discuss with your doctor due to bleeding risks

Protective Factors

Research has identified several factors that may protect against colorectal cancer:

• Calcium and vitamin D: Adequate intake may modestly reduce risk
• Folate: Found in leafy greens, may protect against colorectal cancer
• Garlic: Some evidence suggests protective effects
• Fiber: High-fiber diets consistently associated with lower risk
• Fish: Higher fish consumption associated with lower risk

What Is Life Like After Colorectal Cancer Treatment?

Life after colorectal cancer treatment involves regular surveillance for recurrence (colonoscopy, CEA blood tests, CT scans), managing long-term side effects (bowel function changes, peripheral neuropathy, fatigue), and making healthy lifestyle choices. Most patients return to normal activities within weeks to months after surgery. Support groups and survivorship programs can help address physical and emotional challenges.

Recovery from colorectal cancer treatment varies depending on the treatment received. After surgery, hospital stays typically range from 3-7 days for open procedures and 1-4 days for minimally invasive approaches. Full recovery takes several weeks, during which patients gradually increase activity and adjust to any changes in bowel function.

Bowel function changes are common after colorectal surgery. Many patients experience more frequent bowel movements, urgency, or difficulty controlling bowel movements, especially after rectal cancer surgery. These symptoms usually improve over the first year but may persist long-term for some patients. Dietary modifications, medications, and pelvic floor exercises can help manage these symptoms.

Some patients require a stoma (colostomy or ileostomy) either temporarily or permanently. While adjusting to life with a stoma presents challenges, most people adapt well and return to normal activities including work, exercise, travel, and intimacy. Ostomy nurses and support groups provide valuable guidance and encouragement.

Follow-Up Care and Surveillance

Regular follow-up is essential to detect any cancer recurrence early when treatment may still be curative. Typical surveillance protocols include:

• Clinical visits: Every 3-6 months for the first 2 years, then every 6 months for years 3-5
• CEA blood test: Every 3-6 months for 5 years (for stage II-III cancers)
• CT scan: Annually for 5 years (for stage II-III cancers)
• Colonoscopy: 1 year after surgery, then every 3-5 years if normal

Managing Long-Term Effects

Some treatment side effects may persist or emerge after treatment completion:

• Peripheral neuropathy: Numbness or tingling in hands and feet from oxaliplatin may persist; physical therapy and medications can help
• Chronic fatigue: Common after any cancer treatment; regular exercise actually improves energy levels
• Bowel function changes: May include frequency, urgency, or incontinence; dietary changes and pelvic floor therapy help
• Emotional challenges: Anxiety about recurrence is normal; support groups and counseling are beneficial
• Sexual function: Particularly after rectal cancer surgery; treatable in most cases