Colon cancer

Disease Description (Causes and Symptoms)

• Definition: Colon cancer is a malignant tumor arising from the mucosa of the colon or rectum, and commonly occurs in the sigmoid colon and rectum.
• Pathophysiology: It generally follows the “adenoma–carcinoma sequence,” progressing from normal mucosa → adenoma (polyp) → advanced adenoma → cancer; this process usually takes 10–18 years (7–10 years for polyp formation, 3–8 years from polyp to cancer).
• Causes
  • Genetic factors: Familial diseases account for approximately 10–30% of all cases (familial polyposis, hereditary nonpolyposis colorectal cancer, etc.).
  • Environmental and lifestyle factors: Excessive consumption of animal fat and red meat, insufficient fiber, obesity (associated with insulin resistance and IGF-1), smoking, heavy alcohol consumption, etc.
• Main symptoms
  • Many cases are asymptomatic in the early stages. As the disease progresses, symptoms may include changes in bowel habits, bloody stool (hematochezia or melena), mucous stool, a feeling of incomplete evacuation, decreased stool caliber, abdominal pain, indigestion, weight loss, and anemia due to chronic blood loss (dizziness, tachycardia, shortness of breath).
  • Characteristics according to lesion location: Right-sided colon cancer commonly causes anemia, black stool, and an abdominal mass, whereas left-sided colon cancer commonly causes changes in bowel habits, a feeling of incomplete evacuation, hematochezia, narrowed stool, and symptoms of intestinal obstruction.

Treatment Methods (Including Standard Treatment, Medications, Procedures/Surgery, and Lifestyle Management) and Precautions

• Principle before treatment: A treatment plan is established according to the stage (depth of cancer invasion, lymph node involvement, and presence or absence of metastasis).
• Endoscopic treatment
  • Lesions limited to the mucosa or submucosa: Complete cure may be possible with colonoscopic resection (polypectomy, EMR, ESD). If there is no residual cancer or lymphovascular invasion at the resection margin, additional surgery is unnecessary.
• Surgical treatment
  • Curative surgery: Performed mainly in stages II and III. The involved segment of bowel (right or left hemicolectomy), anterior resection, abdominoperineal (pelvic) resection, etc., is performed together with en bloc removal of the corresponding mesentery, blood vessels, and lymph nodes (lymph node dissection).
  • Depending on whether anal function can be preserved, surgery is classified as low anterior resection (sphincter preservation) versus abdominoperineal resection (removal of the anus).
  • Minimally invasive approaches (laparoscopy and robotic surgery) may be possible, and the method is determined according to the patient’s condition, lesion characteristics, and surgeon’s experience.
  • Palliative surgery: Performed in advanced cancer to relieve symptoms (such as obstruction, bleeding, and pain), including ostomy formation and bypass surgery.
• Chemotherapy
  • Adjuvant therapy (after surgery): Mainly administered for stage III and high-risk stage II disease. Examples of standard regimens include FOLFOX (5-FU/leucovorin/oxaliplatin) and CAPOX (capecitabine + oxaliplatin).
  • Metastatic disease (systemic therapy): Depending on the indication, treatment may include combination therapy with targeted therapy (e.g., bevacizumab, an anti-VEGF agent) or anti-EGFR antibodies (for patients without RAS mutations).
  • Immunotherapy: Immune checkpoint inhibitors (e.g., pembrolizumab) may be used in patients with MSI-H or deficient DNA MMR.
• Radiation therapy
  • Mainly used for rectal cancer (as adjuvant therapy before or after surgery). Preoperative radiation or concurrent chemoradiation may reduce tumor size and help preserve the anus.
• Follow-up examinations (surveillance)
  • Monitor for recurrence and metastasis through postoperative CEA (tumor marker) measurements, regular colonoscopy (to check for recurrence or new polyps), and imaging tests (CT).
• Lifestyle management and prevention
  • Diet: Limit red meat and high-fat intake, and increase consumption of fruits, vegetables, and fiber.
  • Manage weight, stop smoking, limit alcohol, and exercise regularly. Regular checkups are recommended according to public health guidelines.
• Precautions and complications
  • After surgery: Bleeding, infection, intestinal adhesions, urinary and sexual dysfunction due to pelvic nerve damage, and the need for ostomy-related care.
  • Adverse effects of chemotherapy and radiation: Vomiting, decreased appetite, diarrhea, peripheral neuropathy (oxaliplatin), bone marrow suppression, kidney and liver toxicity, and radiation-induced proctitis and skin necrosis.
  • Emergency signs: If severe abdominal pain, symptoms of intestinal obstruction, persistent or heavy bleeding, high fever, or other symptoms occur, visit a medical institution immediately.

Checklist Before an Outpatient Visit (Items to Prepare, Things to Confirm, and Example Questions)

• Items to prepare (recommended to bring)
  • A list of current medications (including prescriptions, OTC medications, and supplements) and any drug allergies
  • Previous test results: Colonoscopy findings, biopsy results (pathology report), abdominal CT/MRI reports, and recent blood test results (FBC, CEA, etc.)
  • Family history (colon cancer, polyps, and hereditary cancer syndromes) and a history of previous polyps or colon surgery
  • Symptom records: When symptoms began, the appearance of bloody stool (bright red/black), the type and duration of changes in bowel habits, weight changes, and the nature of the pain
• Examples of useful questions to confirm during an outpatient visit (patients may record these themselves)
  • Is the blood in the stool bright red or black (suggesting upper gastrointestinal bleeding)? How often does it occur?
  • What are the caliber and shape of the stool (such as narrowing), and is there a feeling of incomplete evacuation after bowel movements?
  • Has there been a change in weight (how many kilograms lost recently), and are there fatigue or dizziness (symptoms of anemia)?
  • Is there a family history of colon cancer or multiple polyps?

Examples of General Questions to Ask the Doctor

• "What is the exact classification of my cancer stage, and what does it mean? What is the outlook for my prognosis (survival rate)?"
• "What are the recommended treatment options (surgery, chemotherapy, and radiation), and what are the advantages, disadvantages, and expected adverse effects of each method?"
• "If surgery is necessary, how will it affect anal function (bowel and sexual function), and how likely is an ostomy?"
• "What is the recurrence surveillance plan (types and intervals of tests), and what lifestyle changes should I make in particular?"

Examples of Disease-Specific Questions (Colorectal Cancer, 2 Questions)

• "What are the tumor differentiation, the degree of invasion into the mucosa, submucosa, and muscular layer, and the presence or absence of lymphatic or vascular invasion in the biopsy results? How will these results affect the treatment plan?"
• "Have molecular tests of the tumor (MSI/MMR status, KRAS/NRAS/BRAF, etc.) been performed? Depending on the results, could targeted therapy or immunotherapy be used?"

(If necessary, bring your test results, pathology report, and image interpretation reports and discuss them in detail with your treating doctor.)