Gastrointestinal Neoplasms: High-Yield Exam Review

## Summary This article provides an exam-focused overview of common and high-yield gastrointestinal tumours, covering the oesophagus, stomach, and colon/appendix. It emphasizes key clinical features, risk factors, pathogenesis, histological differentiators, and genetic pathways crucial for understanding disease progression and diagnosis. Special attention is given to distinguishing features, common precursors, and prognostic indicators to aid in effective study for medical examinations. ## Key Points - **Oesophageal Adenocarcinoma**: Arises in the distal 1/3 of the oesophagus, strongly linked to Barrett oesophagus (columnar metaplasia due to chronic GERD) and TP53 mutations. Predominant in white males in Western countries. - **Oesophageal Squamous Cell Carcinoma (SCC)**: Typically affects the middle 1/3 of the oesophagus. Key risk factors are synergistic alcohol and tobacco use. Associated with squamous dysplasia and potentially HPV in high-risk regions. - **Gastric Adenocarcinoma**: Classified as intestinal or diffuse type. The diffuse type is characterized by signet ring cells and linitis plastica ("leather bottle stomach"). *H. pylori* infection is a major risk factor for both types. - **Gastric MALT Lymphoma**: A primary gastric lymphoma developing in response to chronic *H. pylori* gastritis. Early-stage disease often regresses with *H. pylori* eradication. - **Carcinoid Tumours**: Neuroendocrine tumours most common in the GIT, especially the small intestine (most aggressive) and appendix (almost always benign). Carcinoid syndrome occurs with liver metastases. - **Gastrointestinal Stromal Tumour (GIST)**: The most common mesenchymal tumour of the abdomen, primarily in the stomach. Arises from Interstitial Cells of Cajal with activating mutations in *c-KIT* or *PDGFRA*, responsive to tyrosine kinase inhibitors like Imatinib. - **Colorectal Adenomas**: Premalignant neoplastic polyps characterized by cytologic dysplasia. Sessile serrated adenomas lack dysplasia but are also premalignant. - **Familial Adenomatous Polyposis (FAP)**: Autosomal dominant condition due to an *APC* gene mutation, leading to >100 adenomatous polyps and near-certain colorectal cancer by age 30 if untreated. Represents the chromosomal instability pathway. - **Hereditary Non-Polyposis Colorectal Cancer (HNPCC/Lynch Syndrome)**: Caused by defects in DNA mismatch repair genes (*MLH1*, *MSH2*). Characterized by fewer polyps than FAP but an increased risk of colorectal and extracolonic cancers via the microsatellite instability pathway. - **Colorectal Cancer Prognosis**: Primarily determined by the depth of invasion (T stage) and the presence or absence of lymph node metastases (N stage). - **Pseudomyxoma Peritonei**: A severe complication of mucin-producing appendiceal tumours, leading to the abdomen filling with tenacious mucin, managed by debulking but ultimately fatal. ## Detailed Notes ### I. OESOPHAGUS **1. Oesophageal Adenocarcinoma** This rapidly increasing cancer primarily affects white males in Western countries. Its development is a classic example of metaplasia-dysplasia-carcinoma sequence: * **Pathogenesis**: Chronic GERD leads to **Barrett oesophagus** (intestinal metaplasia of squamous epithelium). Accumulation of genetic (e.g., *TP53* mutation) and epigenetic changes drives progression through low-grade and high-grade dysplasia to invasive adenocarcinoma. * **Morphology**: Typically located in the **distal 1/3** of the oesophagus, often invading the gastric cardia. Microscopically, it's a mucin-producing, gland-forming tumour, frequently with adjacent Barrett oesophagus. **2. Oesophageal Squamous Cell Carcinoma (SCC)** More common in adults >45, especially African Americans and in specific high-incidence regions globally. * **Risk Factors**: Alcohol and tobacco use are **synergistic**. Other risks include poverty, nutritional deficiencies, caustic injury, achalasia, Plummer-Vinson syndrome, very hot beverages, and, in high-risk regions, HPV. * **Pathogenesis**: Progression from normal squamous epithelium through squamous dysplasia (an in situ lesion) to invasive SCC. * **Morphology**: Most often found in the **middle 1/3** of the oesophagus. Early lesions are plaque-like; later stages can be polypoid, ulcerated, or diffusely infiltrative. Microscopic features include squamous differentiation. * **Spread**: Rich submucosal lymphatics allow for widespread local and longitudinal spread, including "skip lesions." Lymph node metastasis patterns vary by location: upper 1/3 to cervical nodes, middle 1/3 to mediastinal nodes, lower 1/3 to gastric/coeliac nodes. Local invasion can lead to tracheoesophageal fistulas (aspiration pneumonia) or aortic haemorrhage. **Clinical Features (Both Oesophageal Tumours)** Symptoms like progressive dysphagia, odynophagia, weight loss, and haemorrhage usually indicate advanced disease. Tracheoesophageal fistulas can present with aspiration. **High-Yield Differentiators: