Gastrointestinal Pathology Practice Questions

Q: A genetic study identifies a family with multiple members having early-onset colorectal cancer. DNA mismatch repair gene testing reveals a mutation in MLH1 gene. Which molecular phenomenon would be most prominently observed in tumor cells from these patients?

Microsatellite instability (MSI). ***Microsatellite instability (MSI)*** - Mutations in **MLH1** lead to defective **DNA mismatch repair (MMR)**, which is the hallmark of **Lynch syndrome** (HNPCC). - Failure to repair errors in repetitive DNA sequences results in **microsatellite instability**, characterized by the expansion or contraction of short tandem repeats in tumor cells. *Chromosomal translocations* - These are typical of **hematologic malignancies** (e.g., Philadelphia chromosome in CML) or certain sarcomas, rather than MMR defects. - Lynch syndrome tumors usually exhibit **diploidy** and stable karyotypes compared to tumors following the **chromosomal instability (CIN)** pathway. *Telomere shortening* - This is a feature of **cellular senescence** and aging, where repeating sequences at the end of chromosomes are lost over time. - Cancer cells generally find ways to **maintain telomere length** (via telomerase) rather than experiencing shortening, which would limit their proliferative capacity. *DNA methylation* - While **hypermethylation** of the MLH1 promoter can cause sporadic MSI, this case specifies a **germline mutation** in a genetic study context. - Methylation is an **epigenetic modification** that affects gene expression but is not the primary molecular consequence arising directly from the loss of DNA repair enzyme function.

Q: What is the most common neoplasm of the appendix?

Carcinoid. **Explanation:** The appendix is a unique anatomical site where neuroendocrine tumors (NETs) are the most frequent primary malignancy. **Why Carcinoid is Correct:** **Carcinoid tumors** (Well-differentiated Neuroendocrine Tumors) are the most common neoplasms of the appendix, accounting for approximately **50-85%** of all appendiceal tumors. They are usually discovered incidentally during appendectomy for suspected appendicitis. Most are located at the **tip of the appendix**, are less than 1 cm in size, and rarely metastasize. **Why other options are incorrect:** * **Pseudomyxoma peritonei:** This is a clinical condition (gelatinous ascites) resulting from the rupture of an appendiceal mucinous neoplasm; it is a consequence of a tumor, not the primary tumor type itself. * **Adenocarcinoma:** This is the second most common primary malignancy of the appendix but is significantly rarer than carcinoid tumors. It typically presents in older age groups and behaves more aggressively. * **Lymphoma:** Primary appendiceal lymphoma is extremely rare, accounting for less than 2% of appendiceal specimens. **High-Yield Clinical Pearls for NEET-PG:** * **Location:** Most appendiceal carcinoids occur at the **distal tip** (75%). * **Management:** * Tumor ** 2 cm**: Requires **Right Hemicolectomy**. * Tumor **1-2 cm**: Appendectomy is usually enough unless there is mesoappendiceal involvement or high-grade features. * **Carcinoid Syndrome:** Rarely occurs with appendiceal carcinoids unless there are extensive liver metastases. * **Most common site for Carcinoid:** Overall, the **rectum** or **small intestine** (ileum) are now often cited as more common sites in recent registries, but for the **appendix specifically**, carcinoid remains the #1 neoplasm.

Q: What is the most common site for leiomyoma in the gastrointestinal tract?

Stomach. **Explanation:** **Leiomyomas** are benign smooth muscle tumors that can occur anywhere in the gastrointestinal (GI) tract where smooth muscle is present. **Why the Stomach is Correct:** The **stomach** is the most common site for leiomyomas in the GI tract, followed by the esophagus. They typically arise from the *muscularis propria* or *muscularis mucosae*. While GISTs (Gastrointestinal Stromal Tumors) were historically misclassified as leiomyomas, true leiomyomas are still most frequently identified in the gastric wall during endoscopic or histological examinations. **Why Other Options are Incorrect:** * **Appendix:** Leiomyomas are extremely rare in the appendix; the most common mesenchymal tumor here is the neuroma, and the most common primary tumor is the carcinoid (neuroendocrine) tumor. * **Jejunum and Ileum:** While smooth muscle tumors occur in the small intestine, they are significantly less common than in the stomach. In the small bowel, GISTs are more prevalent than true leiomyomas [1]. **High-Yield Clinical Pearls for NEET-PG:** * **Histology:** Leiomyomas consist of bundles of spindle-shaped cells with "cigar-shaped" nuclei and no significant atypia or mitotic activity. * **Immunohistochemistry (IHC):** True leiomyomas are **SMA (Smooth Muscle Actin) positive** and **Desmin positive**, but **CD117 (c-KIT) and DOG-1 negative** (this distinguishes them from GISTs) [1]. * **Most common mesenchymal tumor of the GI tract:** GIST (not leiomyoma) [1]. * **Most common site for GIST:** Stomach (60%) [1]. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. The Gastrointestinal Tract, pp. 783-784.

Question 1

A 60-year-old male chronic smoker presents with a non-healing ulcer on the lower lip for 4 months. The lesion has raised everted edges and an indurated base. A biopsy is taken from the edge of the ulcer. The histology is shown in Image 1. Which of the following best describes the structural feature that most directly confirms the cell of origin of this neoplasm?

Accepted Answer

A. Concentric whorls of keratinized cells with intercellular bridges

Answer

B. Glandular acinar formation with mucin secretion

Answer

C. Small round blue cells arranged in sheets with nuclear molding

Answer

D. Spindle-shaped cells in a storiform pattern with pleomorphic nuclei

Question 2

A genetic study identifies a family with multiple members having early-onset colorectal cancer. DNA mismatch repair gene testing reveals a mutation in MLH1 gene. Which molecular phenomenon would be most prominently observed in tumor cells from these patients?

Accepted Answer

Microsatellite instability (MSI)

Answer

Chromosomal translocations

Answer

Telomere shortening

Answer

DNA methylation

Question 3

A 28-year-old man presents with difficulty swallowing solids and liquids for 2 years. Esophageal manometry shows aperistalsis in the distal esophagus and incomplete lower esophageal sphincter (LES) relaxation with wet swallows. Resting LES pressure is 45 mmHg (normal 10-30 mmHg). What is the underlying pathophysiologic defect?

Accepted Answer

Loss of inhibitory nitric oxide-producing neurons in myenteric plexus

Answer

Increased sensitivity of LES smooth muscle to gastrin

Answer

Hyperactivity of excitatory cholinergic neurons

Answer

Fibrosis of LES smooth muscle from chronic inflammation

Answer

Autoantibodies against nicotinic acetylcholine receptors

Question 4

What is the most common neoplasm of the appendix?

Accepted Answer

Carcinoid

Answer

Pseudomyxoma peritonei

Answer

Adenocarcinoma

Answer

Lymphoma

Question 5

What is the most common site for leiomyoma in the gastrointestinal tract?

Accepted Answer

Stomach

Answer

Appendix

Answer

Jejunum

Answer

Ileum

Gastrointestinal Pathology — MCQs

Gastrointestinal Pathology — MCQs

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