Molecular Pathology Practice Questions

Q: Stellate granuloma is found in which condition?

Cat scratch disease. **Explanation:** **Cat scratch disease (CSD)**, caused by the Gram-negative bacterium *Bartonella henselae*, is the classic condition associated with **stellate granulomas**. Pathologically, these are characterized by central irregular (star-shaped) areas of **suppurative necrosis** (containing neutrophils) surrounded by a rim of palisading epithelioid histiocytes and lymphocytes. This unique combination of granulomatous and suppurative inflammation is a hallmark of CSD, typically seen in the regional lymph nodes draining the site of a cat scratch or bite. **Analysis of Incorrect Options:** * **Leprosy:** Characterized by non-caseating granulomas (Tuberculoid) or diffuse histiocytic infiltration without well-formed granulomas (Lepromatous). Stellate morphology is not seen. * **Coccidioidomycosis:** Typically presents with granulomas containing thick-walled **spherules** filled with endospores. While it can cause suppuration, it does not form the characteristic stellate pattern. * **Histoplasmosis:** Features granulomas containing small, intracellular yeast cells (2-4 µm) with a "pseudo-capsule," often found within macrophages. **High-Yield Clinical Pearls for NEET-PG:** * **Differential Diagnosis of Stellate Granulomas:** Apart from Cat scratch disease, stellate granulomas are also seen in **Lymphogranuloma Venereum (LGV)** and occasionally in **Tularemia**. * **Warthin-Starry Stain:** This silver stain is the gold standard for visualizing *Bartonella henselae* in tissue sections. * **Clinical Presentation:** CSD usually presents as painful regional lymphadenopathy (most commonly axillary or cervical) in a child or young adult following contact with a kitten.

Q: A tumor that is negative for CK7 and CK20 is most likely which of the following?

Prostate carcinoma. In immunohistochemistry (IHC), the combination of **Cytokeratin 7 (CK7)** and **Cytokeratin 20 (CK20)** is a fundamental diagnostic algorithm used to determine the primary site of an unknown metastatic tumor. ### **Explanation of the Correct Answer** **A. Prostate Carcinoma:** Most prostate adenocarcinomas are characteristically **CK7 negative and CK20 negative** [1]. This "double negative" profile is a high-yield diagnostic marker. To confirm prostate origin, pathologists typically use more specific markers like **PSA (Prostate Specific Antigen)** or **PSMA** [1]. ### **Analysis of Incorrect Options** * **B. Colon Carcinoma:** Classically follows a **CK7– / CK20+** pattern. This is the "signature" profile for colorectal adenocarcinoma. * **C. Urothelial Carcinoma:** Typically shows a **CK7+ / CK20+** (double positive) pattern. This helps differentiate it from prostate cancer, which often presents with similar clinical symptoms. * **D. Mesothelioma:** Characteristically **CK7+ / CK20–**. It also expresses specific markers like Calretinin and WT-1. ### **High-Yield Clinical Pearls for NEET-PG** * **CK7+/CK20– Profile:** Seen in Lung (adenocarcinoma), Breast, Thyroid, and Endometrial cancers. * **CK7–/CK20+ Profile:** Highly suggestive of Colorectal cancer and Merkel cell carcinoma. * **CK7+/CK20+ Profile:** Seen in Urothelial (Bladder), Pancreatic, and Gastric cancers. * **CK7–/CK20– Profile:** Seen in **Prostate cancer**, Renal Cell Carcinoma (RCC), and Hepatocellular Carcinoma (HCC) [1]. * **Memory Aid:** "Prostate and Kidney (RCC) are 'double negative' (7-/20-), while the Bladder (Urothelial) is 'double positive' (7+/20+)." **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. The Lower Urinary Tract and Male Genital System, pp. 989-994.

Q: ATM mutation is seen in which of the following conditions?

Ataxia telangiectasia. **Explanation:** **1. Why Ataxia Telangiectasia is correct:** Ataxia Telangiectasia (AT) is an autosomal recessive multisystem disorder caused by mutations in the **ATM (Ataxia-Telangiectasia Mutated) gene** located on **chromosome 11q22-23**. The ATM protein is a critical serine/threonine kinase that senses **double-stranded DNA breaks** [1]. Upon detecting damage, it activates p53 and other checkpoint proteins to halt the cell cycle or initiate repair. A mutation leads to genomic instability, clinical ataxia, oculocutaneous telangiectasia, and profound radiosensitivity [1]. **2. Why the other options are incorrect:** * **Fragile X Syndrome:** Caused by a **CGG trinucleotide repeat expansion** in the **FMR1 gene** on the X chromosome, leading to hypermethylation and gene silencing. * **Joubert Syndrome:** A ciliopathy characterized by the "molar tooth sign" on MRI. It is genetically heterogeneous, involving mutations in genes like **INPP5E or TMEM67**, but not ATM. * **Spinocerebellar Ataxia (SCA):** Most common forms (SCA1, 2, 3) are caused by **CAG trinucleotide repeats** (polyglutamine diseases) in various genes (e.g., ATXN1), not ATM [1]. **3. High-Yield Clinical Pearls for NEET-PG:** * **Classic Triad:** Progressive cerebellar ataxia, oculocutaneous telangiectasias, and recurrent sinopulmonary infections (due to **IgA deficiency**). * **Laboratory Marker:** Characteristically elevated **Alpha-Fetoprotein (AFP)** levels in children. * **Malignancy Risk:** Patients have a 100-fold increased risk of developing lymphomas and leukemias. * **Diagnostic Hallmark:** Increased sensitivity to **ionizing radiation** (due to defective DNA repair). **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. The Central Nervous System, pp. 1300-1301.

Question 1

Chromosomal instability syndrome is

Accepted Answer

All of the above

Answer

Fanconi syndrome

Answer

Ataxia Telangectasia

Answer

Bloom syndrome

Question 2

Stellate granuloma is found in which condition?

Accepted Answer

Cat scratch disease

Answer

Leprosy

Answer

Coccidomycosis

Answer

Histoplasmosis

Question 3

Which of the following statements regarding fluorescence in situ hybridization (FISH) is false?

Accepted Answer

In the process, clones are labeled with fluorescent dyes and applied to the metaphase of the cell cycle.

Answer

FISH uses DNA probes that recognize sequences specific to particular chromosomal regions.

Answer

Multiple chromosomes can be detected simultaneously by introducing spectral karyotyping.

Answer

FISH can also be performed on prenatal samples.

Question 4

A tumor that is negative for CK7 and CK20 is most likely which of the following?

Accepted Answer

Prostate carcinoma

Answer

Colon carcinoma

Answer

Urothelial carcinoma

Answer

Mesothelioma

Question 5

Distinction between a poorly differentiated carcinoma and a lymphoma can be made by immunoperoxidase staining of the tumour tissue with antibodies directed against which of the following?

Accepted Answer

Cytokeratin

Answer

Desmin

Answer

Myoglobin

Answer

Vimentin

Question 6

What is the principle of the Prussian blue stain?

Accepted Answer

Oxidation of ferrocyanide to ferric ferrocyanide

Answer

Oxidation of ferrous iron to ferricyanide

Answer

Oxidation of ferroferricyanide to ferrocyanide

Answer

Oxidation of ferrocyanide to ferricferrocyanide

Question 7

Which of the following statements about BCR-ABL 'traits' is NOT true?

Accepted Answer

P190 BCR-ABL fusion protein is associated with an indolent clinical course.

Answer

P190 BCR-ABL fusion protein is considered a bad prognostic factor.

Answer

P230 BCR-ABL fusion protein is positive in chronic neutrophilic leukemia.

Answer

P230 BCR-ABL fusion protein is associated with an indolent clinical course.

Question 8

Which organ is most commonly associated with a red infarct?

Accepted Answer

Small intestine

Answer

Kidney

Answer

Spleen

Answer

Heart

Question 9

Which of the following is true about Nodular Regenerative Hyperplasia?

Accepted Answer

Portal hypertension seen in 50% of patients

Answer

Nodule size 0.1 to 1 cm

Answer

Fibrosis septa present

Answer

AST and ALT are markedly elevated

Question 10

ATM mutation is seen in which of the following conditions?

Accepted Answer

Ataxia telangiectasia

Answer

Fragile X syndrome

Answer

Joubert syndrome

Answer

Spinocerebellar ataxia

Molecular Pathology — MCQs

Molecular Pathology — MCQs

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