📚 Gastroenterology (Git) — L2: Gastrointestinal Tumors

📚 Lecture Overview

This lecture covers gastrointestinal tumors, detailing their classifications, risk factors, and pathophysiology across the esophagus, colon, and stomach. Understanding these malignancies is critical for recognizing clinical presentations, implementing screening modalities, and applying appropriate management strategies like staging, surgery, and palliation.

🎯 Key Concepts & Definitions

• Tumor: Uncontrolled proliferation of cells which may be benign, premalignant, or malignant.
• Benign Tumor: Cells grow as a compact mass and remain strictly at their site of origin.
• Premalignant Tumor: Cells are not yet cancerous, but hold the potential to become malignant over time.
• Malignant Tumor: Growth is uncontrolled; cells can invade nearby tissues and organs and spread to distant sites.
• GIST: Gastrointestinal stromal tumor originating from interstitial cells of Cajal, expressing CD117 antigen.
• TNM Staging: System describing primary Tumor depth, Node involvement, and distant Metastasis.

📖 Main Content

General Risk Factors for GI Cancer

• Environmental factors: Tobacco use, heavy alcohol consumption, low fruit and vegetable intake, physical inactivity, and obesity.
• Chronic infections: Chronic Helicobacter pylori, Hepatitis B (HBV), and Hepatitis C (HCV).
• Genetic factors: Hereditary neoplastic syndromes involving DNA repair genes, DNA mismatch repair, and single nucleotide polymorphism (SNP).

Esophageal Cancer

• Histologically divided into Squamous Cell Carcinoma (SCC) and Adenocarcinoma (ADCA).
• Squamous Cell Carcinoma: Most common worldwide, affects the mid-esophagus, and is strongly linked to smoking, alcohol, and HPV.
• Adenocarcinoma: Largely affects white males, often arising from Barrett's Esophagus (BE).
• Clinical Presentation: Progressive dysphagia, odynophagia, weight loss, and cachexia.
• Management: Endoscopic resection (EMR/ESD) for early stage 1A; esophagectomy and chemoradiation for stages T1b-III; palliative stenting for stage IV.

Colorectal Cancer (CRC)

• Fourth most frequently diagnosed cancer; 95% are adenocarcinomas.
• Risk Factors: Age over 65, male sex, Black ethnicity, personal/family history of colorectal neoplasia, and Inflammatory Bowel Disease (IBD).
• Presentation:
• Proximal tumors: Ill-defined abdominal pain, weight loss, and occult bleeding.
• Distal tumors: Altered bowel habits, decreased stool caliber, and hematochezia.
• Screening: Average-risk screening begins at age 50 for non-African Americans and age 45 for African Americans. Colon polyp to cancer transition takes 10-15 years.

Gastric Cancer & GIST

• Gastric Adenocarcinoma: Accounts for 90% of gastric neoplasms, heavily linked to H. pylori and salted/smoked food diets.
• Lauren Classification: Divides gastric cancer into intestinal or diffuse histologic types.
• Paraneoplastic Syndromes: Associated with Trousseau sign (thrombophlebitis), acanthosis nigricans, and Leser-Trélat syndrome.
• Gastric Lymphoma: Accounts for 20% of extranodal lymphomas; includes MALT lymphoma (low-grade, linked to H. pylori) and Diffuse large B-cell lymphoma.
• GIST: Expresses CD117 antigen (C-Kit); high risk defined by tumors >5 cm with >5 mitoses/50 HPF, treated with imatinib.

📊 Visual Learning

💡 Important Points to Remember

• Esophageal SCC is linked to tobacco, alcohol, and the mid-esophagus; Adenocarcinoma is linked to Barrett's Esophagus and the lower esophagus.
• Barrett's Esophagus management includes proton pump inhibitors and radiofrequency ablation (RFA) for dysplasia.
• Colorectal polyp to cancer transition takes a slow 10 to 15 years, making screening highly effective.
• Proximal CRC presents with occult bleeding and anemia; Distal CRC presents with hematochezia and altered stool caliber.
• Screening age: Start at age 50 for average-risk individuals, but at age 45 for African Americans.
• Gastric cancer types: Adenocarcinoma accounts for 90%; Lauren classification divides them into intestinal and diffuse types.
• Paraneoplastic signs: Trousseau sign (thrombophlebitis), Leser-Trélat syndrome, and acanthosis nigricans point toward malignancy.
• Lymph nodes of note: Sister Mary Joseph nodule (periumbilical), Virchow node (left supraclavicular), and Irish node (anterior axillary).
• GIST marker: GIST tumors originate from interstitial cells of Cajal and express CD117 (C-Kit). Target therapy uses imatinib.
• Common Trap: Confusing MALT lymphoma with gastric adenocarcinoma; MALT is strongly associated with H. pylori and can regress with eradication therapy.

⚠️ Common Exam Questions

• MCQ Trick: Examiners often ask about the specific lymph node locations (e.g., matching Virchow node to the left supraclavicular space or Sister Mary Joseph to the periumbilical region).
• Screening Dilemma: Questions frequently test the exact starting age difference for colorectal cancer screening between African Americans (age 45) and non-African Americans (age 50).
• Pathology Trap: Differentiating between proximal and distal colorectal cancer symptoms (proximal = occult blood/pain; distal = bright red blood/stool caliber changes).
• GIST markers: Expect questions testing the specific cell origin (interstitial cells of Cajal) and molecular marker (CD117/C-Kit).

📝 Quick Review Checklist

I can define gastrointestinal tumors and differentiate between benign and malignant types
I understand the risk factors for esophageal, colorectal, and gastric cancers
I can describe the clinical presentation differences between proximal and distal colorectal tumors
I know the screening guidelines and recommended start ages for colorectal cancer
I can explain the Lauren classification of gastric cancer
I understand the pathology and treatment principles for GIST and MALT lymphoma