Special Surgery 18. Malignant Diseases of the Large Intestine: Symptoms, Diagnosis, Treatment

I. Definition, Etiology and Spread

Definition and Epidemiology

• Colorectal cancer: malignant tumor from epithelial lining of colon or rectum
• Most common histology: adenocarcinoma
• 3rd most common cancer and major cause of cancer-related death
• Peak age: 50-70 years; incidence increasing in younger adults
• Most cases are sporadic; minority are hereditary

Etiology and Risk Factors

• Adenoma-carcinoma sequence: adenoma → dysplasia → invasive adenocarcinoma
• Diet: low fiber, fatty/red/processed meat
• Alcohol, smoking, obesity, physical inactivity
• Type 2 diabetes mellitus
• IBD: ulcerative colitis, Crohn colitis
• Hereditary syndromes:

• FAP: APC tumor suppressor gene mutation
• Lynch syndrome / HNPCC: mismatch repair defect → microsatellite instability

Spread

• Local invasion through bowel wall into adjacent organs
• Lymphatic spread to regional mesocolic/mesorectal lymph nodes
• Hematogenous spread: liver most common, lung also common
• Peritoneal seeding / carcinomatosis
• Bone and brain metastases: late stage

II. Clinical Features, Complications and Diagnosis

Clinical Features by Location

1. Proximal / Right-Sided Colon Cancer

• Cecum, ascending colon
• Occult bleeding → iron-deficiency anemia, fatigue, pallor
• Vague abdominal pain
• Weight loss, anorexia
• Melena or dark stool can occur
• Palpable mass possible
• Obstruction less common early because lumen is wider and stool is liquid

2. Distal / Left-Sided Colon Cancer

• Descending colon, sigmoid colon
• Change in bowel habits: constipation, diarrhea, alternating pattern, narrow stool
• Hematochezia / visible bleeding, mucus
• Colicky abdominal pain from partial obstruction
• Mechanical bowel obstruction more common
• Tenesmus if rectal involvement

Complications

• Bowel obstruction
• Perforation
• Bleeding and iron-deficiency anemia
• Abscess or fistula formation
• Liver metastases
• Peritoneal carcinomatosis

Diagnosis

• History: bleeding, bowel habit change, anemia symptoms, abdominal pain, obstruction, weight loss, family history
• Physical examination: abdominal mass, distension, hepatomegaly, ascites
• DRE: mandatory; can detect rectal mass and bleeding
• Labs: CBC for anemia/decreased Hb/Hct, iron deficiency; renal/liver function before CT/treatment
• CEA: baseline and follow-up/recurrence monitoring only; not diagnostic
• FOBT/FIT: screening test; positive result requires colonoscopy
• Colonoscopy + biopsy: gold standard
• CT colonography: alternative if colonoscopy incomplete; cannot biopsy
• CT chest/abdomen/pelvis: staging, liver/lung/peritoneal metastasis
• MRI pelvis: required for rectal cancer local staging

III. Staging and Curative Treatment

TNM and Stage Groups

• Tis: carcinoma in situ / lamina propria
• T1: submucosa
• T2: muscularis propria
• T3: through muscularis propria into pericolorectal tissue
• T4a: serosa / visceral peritoneum
• T4b: adjacent organs/structures
• N0: no regional lymph node metastasis
• N1: 1-3 regional lymph nodes
• N2: 4 or more regional lymph nodes
• M1: distant metastasis

• Stage 0: Tis
• Stage I: T1-2 N0
• Stage II: T3-4 N0
• Stage III: N+
• Stage IV: M1

Treatment by Stage

• Stage 0: endoscopic polypectomy/local excision if complete; surgery if not endoscopically removable
• Stage I: oncologic surgical resection with lymphadenectomy
• Stage II: surgical resection; adjuvant chemotherapy only if high-risk features
• Stage III: surgical resection + adjuvant chemotherapy, commonly FOLFOX/CAPOX-type regimen
• Rectal cancer stage II-III: neoadjuvant chemoradiotherapy → TME surgery ± adjuvant chemotherapy

Surgical Principles and Operations

• Oncologic principle: en bloc bowel resection + regional lymphadenectomy + adequate margins
• Right hemicolectomy: cecum/ascending colon

• Vascular logic: ileocolic, right colic if present, right branch of middle colic; not whole SMA ligation

• Transverse colectomy / extended colectomy: transverse colon depending on exact site
• Left hemicolectomy: descending colon / splenic flexure region
• Sigmoid colectomy: sigmoid colon, with sigmoid vessels/superior rectal pathway depending on level
• Low anterior resection: upper/mid rectal tumors if sphincter can be preserved
• Abdominoperineal resection: low rectal tumors involving sphincter → permanent colostomy
• Hartmann procedure: emergency cases such as mechanical bowel obstruction, perforation or unsafe anastomosis

IV. Stage IV, Palliative Treatment and Follow-Up

Stage IV / Palliative Treatment

• Stage IV: distant metastasis, most commonly liver/lung/peritoneum
• Main treatment: systemic chemotherapy + targeted therapy according to tumor biology and patient fitness
• Examples:

• Chemotherapy: FOLFOX/CAPOX/FOLFIRI-type regimens
• Targeted therapy: anti-VEGF or anti-EGFR in selected molecular settings

• Selected resectable liver/lung metastases: curative-intent metastasectomy/ablation + systemic therapy may be possible
• Obstructing tumor in non-operative/high-risk patient: endoscopic stent in selected left-sided tumors
• Palliative surgery: diverting stoma, bypass, Hartmann/resection in selected obstruction, perforation, bleeding or severe symptoms

Follow-Up

• CEA monitoring if initially useful
• Colonoscopy: detect metachronous cancer/polyps and assess anastomosis if relevant
• CT chest/abdomen/pelvis: metastasis surveillance according to stage/protocol
• Clinical review: recurrence symptoms, bowel function, stoma/anastomosis problems, chemotherapy toxicity

Prognosis

• Depends on TNM stage, tumor grade, margin status and treatment response
• Approximate 5-year survival:

• Stage I: >90%
• Stage II: ~75%
• Stage III: ~50-60%
• Stage IV: <15%, but improving with modern therapy and metastasis surgery in selected patients