Rectal Cancer Clinical Overview
I. The "On-Call" Snapshot
Clinical Significance in Malaysia: This is not a rare disease. Colorectal cancer is the number one cancer in Malaysian men and number two in women. A significant portion of these are rectal, and they often present late. You will see this in ED, in the surgical clinic, and on the wards.
High-Yield Definition: Rectal cancer is an adenocarcinoma arising from the epithelial lining of the rectum, which is defined as the distal 15 cm of the large bowel as measured from the anal verge by rigid proctoscopy.
Clinical One-Liner: Basically, it's a common cancer in our population that causes bleeding, bowel changes, and obstruction, where management is highly dependent on how deep the tumour has gone and whether it has spread.
II. Etiology & Risk Factors
Etiology: Primarily sporadic adenocarcinoma developing from an adenomatous polyp over years (the adenoma-carcinoma sequence). A smaller percentage is due to inherited genetic syndromes.
Risk Factors:
Non-Modifiable:
Age > 50 (though we are seeing it in younger patients).
Personal history of polyps or colorectal cancer.
History of Inflammatory Bowel Disease (Ulcerative Colitis > Crohn's).
Family history of colorectal cancer.
Inherited syndromes (e.g., Lynch Syndrome/HNPCC, Familial Adenomatous Polyposis/FAP).
Modifiable (Relevant to our Malaysian diet & lifestyle):
High intake of red and processed meats.
Low fibre diet (low intake of fruits and vegetables).
Obesity and physical inactivity.
Smoking.
Heavy alcohol consumption.
III. Quick Pathophysiology
The adenoma-carcinoma sequence is key. It's a multi-step process involving mutations in genes like APC, KRAS, and p53. This transforms normal mucosa into an adenomatous polyp, which then becomes dysplastic and finally invades the submucosa, making it malignant. The tumour grows locally, invading through the rectal wall. Because the rectum is in a tight space (the pelvis) and has a rich lymphatic drainage, it can spread to pelvic lymph nodes and nearby organs early. Venous drainage to both the portal (superior rectal vein) and systemic (middle/inferior rectal veins) systems means it can metastasize to the liver and lungs.
IV. Clinical Assessment
Red Flags & Immediate Actions:
Large volume rectal bleeding / hemodynamic instability: Alert senior, secure two large-bore IV cannulas, send GXM, start fluid resuscitation.
Signs of large bowel obstruction (abdominal distension, vomiting, absolute constipation): Alert senior, keep patient nil by mouth (NBM), insert a Ryle's tube on free drainage, get an urgent plain abdominal X-ray, and prepare for potential emergency surgery.
Peritonism (guarding, rebound tenderness): Suspect perforation. Alert surgical senior immediately, resuscitate, and prepare for theatre.
History:
Common (>50%): Change in bowel habit (especially tenesmus, narrowed stools), rectal bleeding (usually bright red, mixed with stool).
Less Common (10-50%): Anemia symptoms (fatigue, dyspnea), unexplained weight loss, abdominal or perineal pain.
Pertinent Negatives: Ask about hemorrhoid symptoms (itch, perianal lump, bleeding that is on the paper or drips after defecation) to help differentiate. Ask about fever and mucus to rule out infective or inflammatory causes.
Physical Examination:
General: Look for pallor (anemia) and cachexia (advanced disease).
Abdomen: Palpate for masses, hepatomegaly (metastases), and ascites. Check for signs of obstruction.
Digital Rectal Examination (DRE) is MANDATORY:
Feel for a mass: Note its location (anterior/posterior/lateral wall), size, distance from the anal verge, and fixity (mobile or tethered to underlying structures like sacrum or prostate).
Check for blood on the glove.
Assess anal sphincter tone, which is crucial for surgical planning.
Inguinal Lymph Nodes: Palpate for any enlarged nodes.
Clinical Pearl: Don't ever attribute rectal bleeding in an older patient to "just hemorrhoids" without performing a DRE and ensuring a scope has been done. That's a classic miss.
V. Diagnostic Workflow
Differential Diagnosis:
Hemorrhoids:
Points For: Bright red bleeding (drips, on paper), perianal itch/lump.
Points Against: No change in bowel habit, no weight loss. DRE is usually normal unless thrombosed.
How to Differentiate: Proctoscopy/Colonoscopy is definitive.
Diverticular Disease:
Points For: Bleeding (can be massive, maroon), lower abdominal pain.
Points Against: Tenesmus is uncommon. Often a history of diverticulosis.
How to Differentiate: Colonoscopy or CT scan.
Infective/Inflammatory Proctitis (e.g., IBD):
Points For: Bleeding, tenesmus, mucus discharge. Patient may be younger.
Points Against: Systemic symptoms like fever are more common. No palpable mass on DRE usually.
How to Differentiate: Colonoscopy with biopsy (histopathology shows inflammation, not malignancy).
Investigations Plan:
Bedside / Initial:
Digital Rectal Exam (DRE): Your first step. Assesses the tumour directly.
First-Line Labs & Imaging:
Full Blood Count (FBC): To check for anemia from chronic bleeding.
Liver Function Test (LFT), Renal Profile (RP): Baseline for fitness for treatment and to check for liver metastases.
Carcinoembryonic Antigen (CEA): This is NOT a screening test. It's a baseline tumour marker for monitoring treatment response and detecting recurrence.
Colonoscopy & Biopsy: This is the gold standard for diagnosis. The entire colon must be visualized to rule out synchronous polyps or cancers. Biopsy confirms adenocarcinoma.
Staging / Gold Standard:
Contrast-Enhanced CT of Thorax, Abdomen, and Pelvis (CT-TAP): To look for distant metastases (liver, lungs, nodes).
High-Resolution Pelvic MRI: This is the most crucial investigation for local staging of rectal cancer. It tells us the tumour depth (T-stage), nodal involvement (N-stage), and most importantly, the relationship of the tumour to the mesorectal fascia (potential circumferential resection margin, CRM). This information determines the need for neoadjuvant therapy.
Endorectal Ultrasound (ERUS): Can be used for very early tumours (T1/T2) to assess depth of invasion with high accuracy, but MRI is the standard for most cases.
VI. Staging & Severity Assessment
We use the TNM (Tumour, Node, Metastasis) staging system, 8th edition. The pelvic MRI is key to determining the clinical stage.
T-stage (Tumour Depth):
T1: Invades submucosa.
T2: Invades muscularis propria.
T3: Invades through muscularis propria into perirectal tissues.
T4: Invades peritoneum or adjacent organs.
N-stage (Nodal Status): Based on number of suspicious regional lymph nodes on MRI.
M-stage (Metastasis): M0 (no distant spread) or M1 (distant spread present), determined by CT-TAP.
Why this matters for management:
Early Disease (some T1/T2, N0): May proceed directly to surgery.
Locally Advanced (T3/T4 or any N+): These patients require neoadjuvant therapy (chemo-radiotherapy) before surgery to shrink the tumour, increase the chance of a clear resection margin, and reduce local recurrence risk.
VII. Management Plan
Management is decided in a Multidisciplinary Team (MDT) meeting involving surgeons, oncologists, and radiologists.
Immediate Stabilisation (ABCDE Plan):
Address any obstruction or perforation as above. Resuscitate, manage bleeding. This is rare but critical.
Definitive Treatment (The Ward Round Plan):
Locally Advanced (cT3/4 or N+): Neoadjuvant Therapy
Long-Course Chemoradiotherapy (LCCRT): The standard in Malaysia. Radiotherapy to the pelvis (approx. 50.4 Gy in 28 fractions over 5.5 weeks) given concurrently with a radiosensitising agent.
Chemotherapy: Typically oral Capecitabine.
Surgery is planned ~8-12 weeks after completing LCCRT to allow for maximal tumour shrinkage.
Surgery: Total Mesorectal Excision (TME)
This is the cornerstone of curative surgery. It involves removing the rectum along with its surrounding envelope of fatty tissue (the mesorectum) which contains the lymph nodes.
Low Anterior Resection (LAR): For mid to upper rectal tumours. The colon is re-joined to the remaining rectum. A temporary ileostomy is often created.
Abdominoperineal Resection (APR): For very low tumours involving the sphincter complex. The rectum and anus are removed, resulting in a permanent colostomy.
Adjuvant Chemotherapy (Post-op):
Offered to high-risk patients (e.g., positive lymph nodes found on final histology) to treat micrometastatic disease.
Regimens are typically 5-FU based, like FOLFOX (5-FU, Leucovorin, Oxaliplatin) or CapeOx (Capecitabine, Oxaliplatin), for about 6 months.
Metastatic Disease (Stage IV):
Treatment is primarily palliative chemotherapy. The goal is to control the disease and maintain quality of life. Surgery may be considered for palliation of symptoms like bleeding or obstruction.
VIII. Complications
Immediate (Post-op):
Anastomotic Leak (for LAR): Management: Urgent re-laparotomy, washout, and formation of an end colostomy (Hartmann's procedure).
Surgical Site Infection, Ileus: Management: Antibiotics, NBM, supportive care.
Short-Term:
Chemo/Radiotherapy Side Effects: Diarrhea, skin reactions, fatigue. Management: Symptomatic (loperamide, barrier creams).
Pelvic Sepsis: Management: IV antibiotics, may require radiological drainage.
Long-Term:
Low Anterior Resection Syndrome (LARS): Urgency, frequency, incontinence. Management: Dietary modification, pelvic floor exercises, anti-motility agents.
Sexual/Urinary Dysfunction: Due to pelvic nerve damage. Management: Urologist/specialist referral.
Stoma Complications: Retraction, stenosis, parastomal hernia. Management: Stoma nurse specialist review.
IX. Prognosis
Prognosis is highly dependent on the stage at diagnosis. Unfortunately, data from the Malaysian National Cancer Registry (2012-2016) shows over 70% of our colorectal cancer patients present at Stage III & IV.
Overall 5-year survival in Malaysia is around 40-50%.
Stage-specific survival (data from Seremban hospital study):
Stage I & II: ~68%
Stage III: ~51%
Stage IV: ~13%
Key Prognostic Factors:
Stage at diagnosis (most important).
Circumferential Resection Margin (CRM) status: A positive margin after surgery is a very poor prognostic factor.
Pathological response to neoadjuvant therapy.
X. How to Present to Your Senior
"Dr, for your review, this is [patient name/age/gender] in [bed number], with a new diagnosis of rectal adenocarcinoma.
Background: He presented with [key symptom, e.g., per-rectal bleeding for 2 months].
Examination: On DRE, there is a hard, fixed mass approximately 5 cm from the anal verge on the posterior wall. Abdomen is soft.
Investigations: Colonoscopy confirmed a tumour and biopsy is adenocarcinoma. Staging CT-TAP shows no distant metastases. The pelvic MRI report suggests a T3N1 tumour with a threatened circumferential resection margin.
Plan: My plan is to discuss this case in the next multidisciplinary team meeting. My impression is he will require neoadjuvant long-course chemoradiotherapy prior to surgical consideration. For now, we are managing his anemia with a blood transfusion. I would like your opinion on this plan."
XI. Summary & Further Reading
Top 3 Takeaways:
DRE is not optional. It's a vital part of the initial assessment.
Pelvic MRI is the key investigation for local staging. It dictates who needs pre-operative treatment.
Management is multidisciplinary. Locally advanced disease (T3/4 or N+) gets neoadjuvant chemoradiotherapy before TME surgery.
Key Resources:
Malaysian CPG for Management of Colorectal Carcinoma (Quick Reference): MOH Quick Reference Guide
UpToDate: Search for "Clinical presentation, diagnosis, and staging of colorectal cancer" and "Neoadjuvant therapy for rectal adenocarcinoma".
Amboss: Search "Rectal Cancer".
