Colon cancer and rectal cancer

Pathophysiology and clinical classification: Colorectal cancer is a malignant tumor that occurs in the cecum, colon, and rectum, and most cases progress from adenomatous polyps to adenocarcinoma. It is classified as colon cancer or rectal cancer based on anatomical location. In particular, the rectum, located in the narrow pelvic cavity, is adjacent to the autonomic nervous system (urinary and sexual functions) and the anal sphincter, requiring a precise balance between oncologic complete resection and functional preservation.

Domestic and international epidemiological statistics:

Ranked 3rd in domestic cancer incidence, the proportion of early-onset colorectal cancer in people under 50 years old is increasing due to Westernized dietary habits and aging.

The 5-year relative survival rate exceeds approximately 74%, and the early localized stage (Stage I) shows a high survival rate of over 94%. Even in Stage IV patients with distant metastasis, 5-year survival rates have improved remarkably compared to the past due to multidisciplinary metastatic lesion resection and advances in targeted and immunotherapy.

Risk of changes in bowel habits and intermittent hematochezia: In the early stages, there are no obvious symptoms, but as the lesion progresses, constipation and diarrhea recur, stool becomes thinner, there is a sensation of incomplete evacuation, mucous stool appears, and bright red or dark red bloody stool occurs. Many cases are mistaken for hemorrhoids and self-treated, causing the opportunity for treatment to be missed.

Fear of intestinal obstruction and permanent stoma: In the case of patients with advanced colorectal cancer, they often visit the emergency room due to sudden abdominal bloating and bowel obstruction, and patients with lower rectal cancer experience extreme psychological anxiety because they have to have their anus removed and wear a permanent colostomy for life due to the tumor being close to the anus.

Golden time for entering tertiary/secondary advanced care: If a colonoscopy reveals a large or pediceless flat lesion (LST) suspected to be malignant, colon cancer biopsy confirms malignancy, or a mass is palpable on rectal digital examination, immediate referral to an advanced/specialized hospital with pelvic MRI, detailed CT, anus-preserving surgery, and stent insertion capabilities is required.

Colonoscopy and invasion assessment:

Differentiation of deep submucosal invasion through analysis of microduct structures (pit pattern) using high-resolution magnifying endoscopy and NBI.

Depending on the size and location of the lesion, perform endoscopic submucosal dissection (ESD) simultaneously with diagnosis to avoid unnecessary open/laparoscopic surgery.

Pelvic high-resolution 3.0T MRI and endorectal ultrasound (ERUS):

Precisely interpret the primary staging (T) of rectal cancer, depth of bowel wall invasion, involvement of the circumferential resection margin (CRM), and extramural vascular invasion (EMVI) to the nearest 1 mm.

Remote metastasis screening and metabolic imaging:

Evaluation of liver, lung, and peritoneal metastasis via contrast-enhanced CT and PET-CT of chest, abdomen, and pelvis.

Molecular Genomic Biomarker Analysis:

MSI (microsatellite instability)/MMR (DNA mismatch repair proteins) testing is conducted to determine responsiveness to immune checkpoint inhibitors (such as Keytruda).

KRAS, NRAS, BRAF V600E gene mutation testing is conducted to establish criteria for selecting targeted therapy (Cetuximab vs Bevacizumab).

Step 1: Confirmation and precise local/distant staging (Day 1 ~ Day 5)

Confirmation of local invasion and metastasis through colonoscopy biopsy, pelvic 3.0T MRI, and thoracoabdominal contrast CT.

Step 2: Establish treatment strategy at the multidisciplinary tumor board (Day 5 ~ Day 7)

Colon cancer: Decision for immediate laparoscopic/robotic complete mesocolic excision (CME).

Locally advanced rectal cancer (T3 or higher or lymph node positive): To increase anal preservation rates and reduce recurrence, priority is given to [Total Neoadjuvant Therapy (TNT)].

Metastatic colorectal cancer: Establish a pathway for simultaneous resection of primary colorectal cancer and liver/lung metastatic lesions following oncologic medical treatment.

Step 3: Precision surgery and early recovery program (Week 2 ~ Week 3)

Minimally invasive (laparoscopic, Da Vinci robot, TaTME) surgery performed. In rectal cancer patients, sphincter preservation is achieved through intersphincteric resection (ISR).

Activation of ERAS (Enhanced Recovery After Surgery) protocol to control postoperative pain, promote early ambulation, and facilitate rapid gastrointestinal function recovery.

Stage 4: Stoma management, bowel rehabilitation, and adjuvant chemotherapy (Week 4 ~)

If a temporary protective stoma is created, stoma reconstruction is performed 3–6 months later. Specialized stoma care by a dedicated stoma nurse and biofeedback bowel rehabilitation.

Oral/intravenous adjuvant chemotherapy (FOLFOX, CAPOX) based on final pathological stage (high-risk Stage 2 and Stage 3) and regular 5-year follow-up.