Gastrointestinal Tract Tumours

Tissues of the Body

Tissues are derived from three primary germ layers, each contributing to distinct structures and functions within the body:

• Ectoderm: The outermost layer gives rise to several key tissues:

  • Some epithelial tissue, specifically in the oesophagus and anus.

  • All nerve tissue, forming the central and peripheral nervous systems.

  • Modified epidermal tissue, including nails, hair, and glands of the skin.

  • Salivary glands and mucous glands of the nose and mouth.

• Mesoderm: The middle layer differentiates into:

  • Muscle tissue, responsible for movement.

  • Fibrous tissue, providing support and structure.

  • Bone and cartilage, forming the skeletal system.

  • Adipose tissue (fat), involved in energy storage and insulation.

  • Blood and lymph vessels, crucial for circulation and immune function.

  • Blood cells, including red and white blood cells.

  • Kidneys, essential for filtration and waste removal.

  • Gonads (ovaries and testes), responsible for reproduction.

• Endoderm: The innermost layer develops into:

  • Epithelial tissue lining the majority of the digestive tract (excluding the open ends).

  • Epithelium lining outpouchings of the digestive tract, such as the biliary, urothelial, and respiratory tracts.

  • Liver, responsible for metabolic functions.

  • Pancreas, producing digestive enzymes and hormones.

  • Thymus, crucial for T-cell maturation.

  • Thyroid and parathyroids, regulating metabolism and calcium levels.

GI Tract Tumours

Tumours of the GI tract can originate from any of the three germ layers, each potentially leading to different types of malignancies:

• Ectoderm: Squamous mucosa, derived from ectoderm, can give rise to squamous cell carcinoma. This type of cancer is often associated with the oesophagus and anus.

• Mesoderm: Vessels and soft tissue, originating from mesoderm, can lead to sarcoma. Sarcomas are less common in the GI tract but can occur in the connective tissues and muscles.

• Endoderm: Glandular mucosa, derived from endoderm, can result in adenocarcinoma. Adenocarcinomas are the most common type of GI cancer, frequently found in the stomach, colon, and rectum.

Malignant Tumours of the GI Tract

The prognosis of a malignant tumour depends mainly on its grade and stage. Higher grade and stage tumours tend to be more aggressive, indicating rapid growth and increased likelihood of metastasis.

Markers used to diagnose GIT carcinoma:

• Serum marker: CEA (Carcinoembryonic antigen) - Elevated levels can indicate the presence of carcinoma, especially colorectal cancer. However, it is not specific and can be elevated in other conditions.

• Tissue marker: CDX-2 (Caudal-related homeobox transcription factor 2) - A transcription factor expressed in the nuclei of intestinal epithelial cells. Useful in identifying the primary site of metastatic adenocarcinomas.

Grade of a Malignant Tumour

The grade indicates how well-differentiated the tumour is, reflecting its resemblance to the original cell type:

• Grade 1: Well-differentiated - The tumour looks like the cell of origin, indicating slower growth and less aggressive behaviour.

• Grade 2 and 3: Moderate & poor differentiation - Tumours show some but not all of the features of the original cells which indicates a higher proliferation rate.

• Grade 4: Undifferentiated - The tumour has lost almost all resemblance to the original cells, indicating rapid growth and aggressive behaviour.

Stage of a Malignant Tumour

Stage indicates how far the tumour has spread and is crucial for determining treatment strategies and predicting prognosis:

• TNM (Tumour, Node, Metastasis) classification: Differs for different tumours, providing a standardized way to describe the extent of the primary tumour (T), involvement of regional lymph nodes (N), and presence of distant metastasis (M).

• Specific classifications for certain tumours (e.g., Dukes’ classification for colorectal cancer): These classifications are tailored for specific cancer types, offering more detailed staging information.

The staging significantly impacts treatment decisions. For example, a colonic tumour staged as T1N0M0 would typically be treated with surgical resection alone, whereas a tumour staged as T3N2M0 would require surgery plus adjuvant chemotherapy to prevent recurrence.

Types of GI Tract Tumours

Common and largely influenced by diet and genetic factors, GI tract tumours can be classified into several types:

• Epithelial:

  • Squamous cell carcinoma: Arising from squamous cells, often found in the oesophagus.

  • Adenocarcinoma: Originating from glandular cells, common in the stomach, colon, and rectum.

  • Neuroendocrine tumours: Arising from neuroendocrine cells, can occur throughout the GI tract.

• Mesenchymal: Gastrointestinal stromal tumours (GISTs) - Tumours of the connective tissues and smooth muscles of the GI tract.

• Haematological: Lymphomas - Cancers of the lymphatic system that can occur in the stomach and intestines.

Oesophageal Carcinoma

Histological classification is divided based on the location within the oesophagus:

• Upper 2/3: Often squamous cell carcinoma, associated with smoking and alcohol, which are major risk factors that cause chronic irritation and inflammation.

• Lower 1/3: Often adenocarcinoma, associated with GORD (Gastro-Oesophageal Reflux Disease) and Barrett’s oesophagus, a condition where the normal squamous epithelium is replaced by columnar epithelium.

Aetiology of Squamous Cell Carcinoma

• Tobacco: Contains carcinogenic compounds that directly damage the DNA of oesophageal cells.

• Alcohol: Contains many carcinogenic compounds and irritates the oesophageal lining, promoting inflammation and cell damage.

• Diet:

  • High nitrite/nitrosamine levels: Found in preserved and processed foods.

  • Smoked fish and fungal contamination: Can introduce carcinogenic substances.

  • Low intake of fresh fruits & vegetables (antioxidants): Antioxidants protect cells from damage caused by free radicals.

Pathogenetic Mechanisms of Squamous Cell Carcinoma

Inflammation (oesophagitis) caused by irritants:

• Leads to epithelial cell damage, disrupting normal cell function.

• Increases epithelial cell turnover, accelerating the risk of errors during cell division.

• Increases risk of dysplasia and then malignancy as abnormal cells proliferate.

The progression:

$Squamous metaplasia \rightarrow Carcinoma in situ \rightarrow Invasive carcinoma$

Pathogenetic Mechanisms of Adenocarcinoma

Reflux of acid/bile leads to epithelial cell damage:

• Increases epithelial cell turnover, promoting cellular changes.

• Leads to metaplasia (squamous → gastric → intestinal-type), where the squamous epithelium is replaced by columnar epithelium.

• Increases the risk of dysplasia and then malignancy because of previous metaplasia.

The progression:

$Normal mucosa \rightarrow Gastric metaplasia (Barretts Oesophagus) \rightarrow Adenocarcinoma$

Oesophageal Carcinoma: Complications and Spread

• Oesophageal obstruction: Tumour growth narrows the oesophageal lumen, causing difficulty in swallowing.

• Hematemesis (vomiting of blood): Erosion of blood vessels by the tumour.

• Tracheo-oesophageal fistula: Abnormal connection between the trachea and oesophagus, leading to coughing and aspiration.

• Spread:

  • Direct: To trachea and mediastinal structures, invading nearby tissues.

  • Lymphatic: Longitudinal extension in submucosal lymphatics, then to supraclavicular (upper ⅓), mediastinal (middle ⅓), or celiac (lower ⅓) nodes.

    • Upper 1/3 = cervical

    • middle and upper ½ of lower third= thoracic

    • lower ½ of lower third (abdominal)= celiac

  • Blood: Late spread to liver, lungs, etc.

Gastric Cancer

Predisposing Factors

• Adenomatous polyps: Precancerous growths that can develop into adenocarcinoma.

• Chronic gastritis and peptic ulcer: Chronic inflammation increases the risk of dysplasia.

• Blood group A: Associated with a slightly higher risk of gastric cancer.

• Diet: Smoked food and food containing nitrates, which can be converted to carcinogenic nitrosamines.

Site Distribution

The percentage can vary in different studies and locations. Common sites include the antrum and body of the stomach.

Gross Picture (Bormann Classification)

• Type I Polypoid: Well-circumscribed polypoid tumours, often protruding into the lumen.

• Type II Fungating: Fungating tumours with marked central infiltration, characterized by an irregular, cauliflower-like appearance.

• Type III Ulcerated: Ulcerated tumours with infiltrative margins, forming deep ulcers with poorly defined edges.

• Type IV Infiltrating: Diffusely infiltrated tumours, spreading along the stomach wall without forming a distinct mass (linitis plastica).

Histologic Classification

• Adenocarcinoma (95%): The predominant type, arising from glandular cells.

• Lymphoma (4%): Cancers of the lymphatic tissue in the stomach.

• Leiomyosarcoma (1%): Rare mesenchymal tumours from smooth muscle cells.

• Rare: Squamous cell carcinoma - Very uncommon in the stomach.

• Metastatic: Colon/pancreas/breast - Cancers from other sites can metastasize to the stomach.

Intestinal vs. Diffuse Gastric Carcinoma

Hereditary Diffuse Gastric Cancer (DGC)

Consider CDH1 testing in the family if:

1. Two or more documented cases of diffuse gastric cancer in first- or second-degree relatives.

2. At least one diagnosed before the age of 50, or three or more first- or second-degree relatives with diffuse gastric cancer at any age.

Management of a CDH1 mutation carrier:

• Endoscopic surveillance is inadequate due to the diffuse nature of the disease.

• Prophylactic gastrectomy may be advised to reduce cancer risk.

• Female carriers also have a 60% lifetime risk of lobular breast carcinoma, necessitating regular screening.

Pathogenesis of Gastric Carcinoma (Intestinal Type)

$Intestinal metaplasia \rightarrow cancer$

Gastric Carcinoma: Diffuse, Signet Ring Type

Signet ring cells lead to linitis plastica, a condition where the stomach wall becomes thickened and rigid.

Gastric Cancer TNM Staging

The TNM Staging should be stated here

Gastric Carcinoma: Spread and Complications

• Spread:

  1. Direct: To pancreas, liver, spleen, and colon, invading adjacent organs.

  2. Lymphatic: To gastric, celiac, para-aortic, and supraclavicular lymph nodes, following the lymphatic drainage pathways.

  3. Blood: To liver, lungs, and bones, spreading through the bloodstream.

  4. Trans-coelomic: Peritoneal deposits and hemorrhagic ascites, seeding cancer cells within the abdominal cavity.

• Complications:

  1. Gastrointestinal bleeding: Hematemesis and melena, caused by tumour erosion of blood vessels.

  2. Pyloric obstruction: Blockage of the pylorus, leading to vomiting and abdominal distension.

  3. Hypochlorhydria and intrinsic factor deficiency (Parietal cells secrete HCL and intrinsic factor): Reduced acid and intrinsic factor production, affecting digestion and B12 absorption.

  4. Anemia due to hemorrhage and intrinsic factor deficiency: Results from chronic blood loss and impaired B12 absorption.

Gastric Sarcoma

Gastrointestinal Stromal Tumour (GIST)

• Most common mesenchymal tumour of the abdomen, arising from connective tissues.

• The stomach is the most frequent site (more than 50%), but can also occur in the small intestine and colon.

• Prognosis correlates with tumour size, mitotic index, and location (gastric GISTs are less aggressive than those in the small intestine). Smaller size and lower mitotic index indicate less aggressive behaviour.

Pathogenesis

• Mutations of the gene encoding tyrosine kinase C-KIT (75-80 %), receptor for stem cell factor. These mutations lead to constitutive activation of the receptor, promoting cell growth.

• Mutations that activate a related tyrosine kinase, platelet-derived growth factor receptor A (PDGFRA). Similar to C-KIT mutations, these drive uncontrolled cell proliferation.

• GISTs appear to arise from, or share a common stem cell with, the interstitial cells of Cajal (ICC). ICCs are specialized cells that regulate gut motility.

• Interstitial cells of Cajal express c-KIT and are located in the muscularis propria; they serve as pacemaker cells for gut peristalsis. Their role makes them susceptible to GIST development.

Morphology

• Gross picture: Solitary, well-circumscribed, fleshy, submucosal mass. The tumours are typically round or oval and can vary in size.

• Metastases may form multiple small serosal nodules or fewer large nodules in the liver. Liver is the most common site for metastasis.

• Microscopic picture: GISTs can be composed of thin, elongated spindle cells or plumper epithelioid cells. The cell type influences the tumour's appearance under the microscope.

• Most specific marker: DOG1 - Discovered on GIST-1, aids in definitive diagnosis.

• Most useful marker: c-KIT (CD117) {targeted therapy} - A tyrosine kinase receptor, targeted by drugs like imatinib.

Lymphoma

Primary lymphomas comprise nearly 5% of all gastric malignancies. Types include:

• Lymphomas of mucosa-associated lymphoid tissue (MALT), or MALTomas (the most common type). These are typically low-grade lymphomas associated with Helicobacter pylori infection.

• Diffuse large B cell lymphoma. A more aggressive type of lymphoma.

Chronic Gastritis and Role of Helicobacter pylori

Pathogenetic mechanisms related to Helicobacter pylori need to be explained here

Small Intestinal Tumours

Uncommon. Types include:

• Adenocarcinoma of ampulla - Arising from the ampulla of Vater.

• Endocrine tumours - Such as carcinoid tumours.

• GIST

• Lymphoma

Large Bowel Tumours

Aetiology and Predisposing Factors

• Diet:

  • Low vegetable fibre intake: Reduces stool bulk and transit time, increasing exposure to carcinogens.

  • High content of refined carbohydrates: Can lead to insulin resistance and inflammation.

  • Diminished vitamin A, C, and E (protective micronutrients): Antioxidants that protect against cell damage.

  • Excess fat intake: Particularly saturated and trans fats, linked to increased risk.

• Genetic factors:

  • Genes increasing adenoma formations. Mutations in APC and other genes.

  • Genetic cancer syndromes (FAP, HNPCC).

• Inflammatory bowel disease: Chronic inflammation increases the risk of dysplasia and cancer.

FAP: Familial Adenomatous Polyposis [mutation of APC gene]

HNPCC: Hereditary Non-Polyposis Colorectal Cancer [ alteration of DNA of mismatch repair gene]

Presenting Symptoms of Colorectal Cancer

1. Change in bowel habits, most common symptom (74%): Altered frequency or consistency of stools.

2. Rectal bleeding in combination with change in bowel habits (51%): Indicates possible tumour erosion.

3. Rectal or abdominal mass (24.5- 12.5%): Palpable lump.

4. Iron deficiency anemia (9.6%): Due to chronic blood loss.

5. Abdominal pain is the least common symptom (3.8%).

Staging of Colorectal Cancer

1. T.N.M. staging:

   • Tis: Carcinoma in situ - Cancer cells are confined to the epithelium.

   • T1: Tumour invades into submucosa

   • T2: Tumour invades musculosa

   • T3: Tumour invades till subserosa

   • T4: Tumour invades visceral peritoneum and may involve nearby tissue or organ

   • N0: no lymph node metastasis

   • N1: metastasis in 1- 3 pericolic or peritoneal nodes

   • N2: metastasis in 4 or more pericolic or peritoneal nodes

   • N3: metastasis in any nodes along the course of major blood vessels.

   • M0: no distant metastasis

   • M1: distant metastasis

2. Dukes’ staging:

   • Dukes’A Tumour confined to bowel wall

   • Dukes’ B Tumour extending through the bowel wall

   • Dukes’ C Regional lymph nodes involved

   • Dukes’ D Metastatic disease

3. Modified Dukes’ staging: Correlates Tumour invasion with both the number of metastatic Lymph Nodes and distant Metastasis

   • Stage A: $T1, N0, M0$

   • Stage B1: $T2$

   • Stage B2: $T3 \text{ or } T4$

   • Stage C1: $T2, N1, 2 \text{ or } 3$

   • Stage C2: $T3 \text{ or } T4$

   • Stage D: Any T, Any N, M1

Carcinoma of the Large Bowel: Pathogenesis

Two separate pathogenic pathways:

• Adenoma-carcinoma sequence

• Inflammation-dysplasia sequence

Adenoma-Carcinoma Sequence

• The initial lesion is a benign tumour – adenoma.

• The degree of dysplasia increases over time. Dysplasia refers to abnormal cell growth.

• Eventually invades through basement membrane, at which point it is an adenocarcinoma.

Genetic mutations of APC, K-ras, and p53 genes; MMR genes (mismatch repair genes).

Inflammation-Dysplasia Sequence

(a less common pathway)

• Inflammatory bowel disease causes chronic inflammation.

• Inflammation leads to epithelial cell damage.

• Increases epithelial cell turnover.

• Increases the risk of dysplasia and then malignancy.

Colonic Adenocarcinoma

Case Studies

Case 1

An omental biopsy shows diffuse infiltration by adenocarcinoma with signet ring cells. The most likely primary site is the stomach.

Case 2

A 56-year-old woman has an ultrasound scan of the liver that reveals multiple deposits consistent with metastases. A liver biopsy shows squamous cell carcinoma. The most likely primary site of the malignancy is the oesophagus.

Case 3

A 68-year-old lady is admitted to hospital with symptoms and signs of large bowel obstruction. At laparotomy, there was evidence of an obstructing lesion at the rectosigmoid junction. An anterior resection is preformed.

1. The most likely histological diagnosis is adenocarcinoma.

2. The histopathology report states: Sections show a moderately differentiated adenocarcinoma which extends through the wall into the subserosa but does not breach the serosal surface. Three lymph nodes show metastatic adenocarcinoma. The high tie node is free of tumour (nodes above the root of the Inferior mesenteric artery).

What is the TNM staging of this tumour? T3N1Mx

Case 4

A 65-year-old man has recently noticed bleeding/rectum. Endoscopy reveals the presence of a malignant fungating mass in the colon. MRI has shown multiple hepatic nodules suggestive of metastasis.

Which is the most specific immunohistochemical marker used to confirm malignancy of primary colon origin in the hepatic nodules? CDX-2.

Question 1

Case: A 58‐year‐old obese man with a long history of gastroesophageal reflux disease (GERD) presents with progressive dysphagia for solids and unintended weight loss. Endoscopy reveals an ulcerated mass in the distal esophagus.

Which histological type is most likely?

A. Squamous cell carcinoma B. Adenocarcinoma C. Gastrointestinal stromal tumor D. Lymphoma E. Neuroendocrine tumor

Answer: B. Adenocarcinoma

Explanation: Adenocarcinoma of the distal esophagus is strongly linked to chronic GERD and Barrett’s esophagus. In contrast, squamous cell carcinoma is more common in the middle to upper esophagus, especially in patients with a history of smoking or alcohol abuse.

Question 2

Case: A 68‐year‐old woman presents with chronic epigastric pain, early satiety, and weight loss. Endoscopy shows a diffusely thickened, rigid stomach with a “leather bottle” appearance (linitis plastica).

Which histopathological description best fits this lesion?

A. Well‐differentiated adenocarcinoma with prominent glandular formation B. Moderately differentiated ulcerated adenocarcinoma C. Diffuse, poorly differentiated adenocarcinoma with signet ring cells D. Squamous cell carcinoma E. Gastrointestinal stromal tumor

Answer: C. Diffuse, poorly differentiated adenocarcinoma with signet ring cells

Explanation: Linitis plastica is the classic gross appearance of diffuse gastric adenocarcinoma, which is characterized by infiltration of signet ring cells leading to diffuse thickening of the stomach wall.

Question 3

Case: A 65‐year‐old heavy smoker and drinker presents with progressive dysphagia. Endoscopy reveals an ulcerated lesion in the mid‐esophagus.

Which histological type does this clinical scenario most likely represent?

A. Adenocarcinoma B. Squamous cell carcinoma C. Gastrointestinal stromal tumor D. Lymphoma E. Neuroendocrine tumor

Answer: B. Squamous cell carcinoma

Explanation: Smoking and alcohol consumption are strong risk factors for squamous cell carcinoma, which typically arises in the upper or mid‐esophagus where the mucosa is squamous epithelium.

Question 4

Case: A 70‐year‐old man presents with melena and iron deficiency anemia. Endoscopy reveals an ulcerated mass in the antrum of the stomach.

Which risk factor is most commonly associated with this type of gastric cancer?

A. Alcohol consumption B. Helicobacter pylori infection C. Obesity D. High‐fiber diet E. NSAID use

Answer: B. Helicobacter pylori infection

Explanation: Helicobacter pylori infection is well known to cause chronic gastritis that can lead to intestinal metaplasia and, ultimately, intestinal‐type gastric adenocarcinoma, most frequently arising in the antrum.

Question 5

Case: A 50‐year‐old man is found to have a large polypoid lesion in the colon on screening colonoscopy. Histopathology demonstrates adenocarcinoma arising from an adenomatous polyp, in keeping with the adenoma‐carcinoma sequence.

Which genetic mutation is typically involved in the early stages of this sequence? (Note: Among the options provided, choose the one most commonly seen in progression from adenoma to carcinoma.)

A. CDH1 mutation B. KRAS mutation C. BRAF mutation D. p16 deletion E. EGFR amplification

Answer: B. KRAS mutation

Explanation: The adenoma‐carcinoma sequence in colorectal cancer usually begins with an APC mutation, followed by additional mutations such as in the KRAS gene and later p53. In these options, KRAS is the critical step in progression from adenoma to carcinoma.

Question 6

Case: A 65‐year‐old man with known colorectal cancer undergoes imaging. The tumor is described as invading through the muscularis propria into the subserosa (but not breaching the serosa), with metastasis in 2 regional lymph nodes and no distant spread on further imaging.

What is the TNM staging for his tumor?

A. T2N0M0 B. T3N1M0 C. T3N0M0 D. T4N2M0 E. T1N1M0

Answer: B. T3N1M0

Explanation: Tumor invasion into the subserosa without serosal breach corresponds to T3. Involvement of 1–3 regional lymph nodes is N1, and the absence of distant metastases is M0.

Question 7

Case: A 56‐year‐old woman undergoes resection of a colonic tumor. The pathology report describes a lesion extending through the bowel wall with metastases in regional lymph nodes, while the high‐tie lymph node (above the root of the inferior mesenteric artery) is free of tumor. Using Dukes’ classification, what stage is most appropriate for her cancer?

A. Dukes’ A B. Dukes’ B C. Dukes’ C D. Dukes’ D E. Not classifiable by Dukes’ criteria

Answer: C. Dukes’ C

Explanation: Dukes’ staging classifies tumors with regional lymph node involvement as Dukes’ C. Dukes A is confined to the bowel wall and Dukes B involves extension without nodal metastasis.

Question 8

Case: A 62‐year‐old man with weight loss and epigastric pain undergoes endoscopy revealing a large fungating mass in the stomach. Immunohistochemical staining of biopsy tissue shows strong positivity for CDX-2.

Which tumor marker does CDX-2 represent for GI malignancies?

A. A serum marker for pancreatic cancer B. A tissue marker specific for gastrointestinal adenocarcinoma C. A marker for gastrointestinal stromal tumors D. A marker of squamous cell differentiation E. A marker for neuroendocrine tumors

Answer: B. A tissue marker specific for gastrointestinal adenocarcinoma

Explanation: CDX-2 is a transcription factor expressed in the nuclei of intestinal epithelial cells and is used as a tissue marker to identify GI adenocarcinomas, particularly of colonic origin.

Question 9

Case: A 45‐year‐old man presents with gastrointestinal bleeding. Endoscopy reveals a well-circumscribed, exophytic polypoid mass in the stomach. According to the Borrmann gross classification of gastric carcinoma, which type does this lesion most likely represent?

A. Type I (polypoid) B. Type II (fungating) C. Type III (ulcerated) D. Type IV (diffusely infiltrative or linitis plastica) E. Type V (cystic degeneration)

Answer: A. Type I (polypoid)

Explanation: Borrmann Type I lesions are polypoid, exophytic masses that are well circumscribed. This contrasts with Type II (fungating or exophytic with central ulceration), Type III (infiltrative ulcerated masses), and Type IV (diffuse infiltration leading to linitis plastica).

Question 10

Case: A 75‐year‐old woman with a long-standing history of ulcerative colitis presents with a change in bowel habits and rectal bleeding. Colonoscopy and biopsy reveal adenocarcinoma of the colon arising in a background of chronic inflammation.

Which sequence is most likely responsible for her malignancy?

A. Adenoma‐carcinoma sequence B. Inflammation‐dysplasia sequence C. De novo carcinoma without precursor lesion D. Viral-induced transformation E. Radiation-induced oncogenesis

Answer: B. Inflammation‐dysplasia sequence

Explanation: Chronic inflammatory bowel disease, such as ulcerative colitis, predisposes to cancer through the inflammation‐dysplasia sequence whereby repeated cycles of inflammation and regeneration lead to dysplasia and malignant transformation.

Question 11

Case: A 52‐year‐old man is found to have a submucosal gastric mass on endoscopy. Endoscopic ultrasound–guided biopsy shows a tumor composed of spindle cells arranged in fascicles. Immunohistochemistry is positive for c-KIT (CD117) and DOG-1.

What is the most likely diagnosis?

A. Gastric adenocarcinoma B. Gastric lymphoma C. Gastrointestinal stromal tumor (GIST) D. Leiomyoma E. Neuroendocrine tumor

Answer: C. Gastrointestinal stromal tumor (GIST)

Explanation: GISTs are the most common mesenchymal tumors of the GI tract and are characteristically positive for c-KIT (CD117) and DOG-1. They often originate from the interstitial cells of Cajal.

Question 12

Case: A 63‐year‐old man with colon adenocarcinoma undergoes staging workup. Imaging reveals multiple liver lesions, and biopsy of one lesion confirms metastases.

What is the most common route of metastasis of colorectal cancer to the liver?

A. Direct invasion B. Lymphatic spread C. Hematogenous spread via the portal circulation D. Transcoelomic spread E. Neural spread

Answer: C. Hematogenous spread via the portal circulation

Explanation: Colorectal cancer most commonly metastasizes to the liver through hematogenous spread via the portal venous system.

Question 13

Case: A 66‐year‐old woman with a family history of gastric cancer undergoes endoscopy. The biopsy reveals intestinal-type adenocarcinoma arising in the background of chronic atrophic gastritis with intestinal metaplasia.

Which environmental factor is most strongly associated with this type of gastric carcinoma?

A. High salt diet B. Alcohol abuse C. Tobacco smoking D. Obesity E. NSAID use

Answer: A. High salt diet

Explanation: A high salt diet—as well as Helicobacter pylori infection—is a known risk factor for the development of intestinal-type gastric adenocarcinoma via chronic gastritis and intestinal metaplasia.

Question 14

Case: A 40‐year‐old woman presents with dyspepsia. Endoscopic biopsy of a gastric lesion shows malignant glandular structures. Serum studies reveal an elevated carcinoembryonic antigen (CEA) level.

What is the primary utility of CEA in gastrointestinal cancers?

A. It is specific for squamous cell carcinoma. B. It is used as a serum marker to monitor tumor burden and recurrence. C. It is exclusively expressed in benign lesions. D. It is diagnostic of gastrointestinal stromal tumors. E. It is a marker for neuroendocrine differentiation.

Answer: B. It is used as a serum marker to monitor tumor burden and recurrence.

Explanation: CEA is widely used as a tumor marker in GI adenocarcinomas to assess treatment response and detect recurrence. It is not specific for squamous cell carcinoma or neuroendocrine tumors.

Question 15

Case: A 68‐year‐old man presents with a several-month history of rectal bleeding and altered bowel habits. Colonoscopy reveals an obstructing lesion at the rectosigmoid junction. Among the common presenting symptoms of colorectal cancer, which one is considered least frequent?

A. Change in bowel habits B. Rectal bleeding C. Iron deficiency anemia D. Abdominal pain E. Palpable abdominal mass

Answer: D. Abdominal pain

Explanation:While changes in bowel habits, rectal bleeding, and anemia are common presentations, abdominal pain is generally noted as the least common presenting symptom in colorectal cancer.