Neoplasia — MCQs

Neoplasia Indian Medical PG Practice Questions and MCQs

Question 401: Cytogenetic studies in a 40-year-old woman with follicular lymphoma demonstrate a t(14;18) chromosomal translocation involving the bcl-2 gene. Constitutive expression of the protein encoded by the bcl-2 gene inhibits which of the following processes in this patient's transformed lymphocytes?

A. Apoptosis (Correct Answer)
B. DNA excision repair
C. G1-to-S cell cycle progression
D. Oxidative phosphorylation

Explanation: **Explanation:** The core concept in this question is the role of the **BCL-2 gene** as an **anti-apoptotic oncogene**. [1], [2] **1. Why Apoptosis is correct:** In Follicular Lymphoma, the characteristic **t(14;18)** translocation moves the *BCL-2* gene (from chromosome 18) to the **Immunoglobulin Heavy Chain (IgH)** locus (on chromosome 14). [1], [4] Because the IgH promoter is highly active in B-cells, this results in the **constitutive overexpression of the BCL-2 protein**. [2] BCL-2 normally resides in the outer mitochondrial membrane and functions by stabilizing the membrane, preventing the release of **Cytochrome C**. [3] By inhibiting the intrinsic (mitochondrial) pathway of apoptosis, B-cells that should normally die (due to lack of selection or mutations) survive indefinitely, leading to the accumulation of neoplastic cells. [1] **2. Why incorrect options are wrong:** * **DNA excision repair:** This process involves enzymes like DNA glycosylases or XP proteins (defective in Xeroderma Pigmentosum). BCL-2 does not directly regulate DNA repair mechanisms. * **G1-to-S progression:** This is regulated by Cyclins (e.g., Cyclin D1) and CDKs. While BCL-2 overexpression promotes survival, it does not directly accelerate the cell cycle; in fact, follicular lymphoma is often characterized by a low proliferative index. [1] * **Oxidative phosphorylation:** While BCL-2 is located on the mitochondrial membrane, its primary role is structural/regulatory regarding permeability, not the metabolic production of ATP. **High-Yield Clinical Pearls for NEET-PG:** * **t(14;18):** Pathognomonic for Follicular Lymphoma. [4] * **BCL-2 vs. BAX:** BCL-2 and BCL-XL are **anti-apoptotic**, whereas BAX and BAK are **pro-apoptotic** (they form pores in the mitochondria). [3] * **Follicular Lymphoma** typically presents as painless, "waxing and waning" lymphadenopathy in older adults. * **BH3-only proteins** (like BIM, BID, BAD) are the sensors that neutralize BCL-2 to initiate cell death. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Diseases of White Blood Cells, Lymph Nodes, Spleen, and Thymus, pp. 602-604. [2] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Neoplasia, pp. 310-311. [3] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Neoplasia, p. 310. [4] Cross SS. Underwood's Pathology: A Clinical Approach. 6th ed. Common Clinical Problems From Diseases Of The Urinary And Male Genital Tracts, pp. 561-562.

Question 402: Which of the following is a metastasis suppressor gene in relation to prostate cancer?

A. KAI-1 (Correct Answer)
B. NM 23
C. KISS
D. p53

Explanation: **Explanation:** **Metastasis suppressor genes** are a distinct class of genes that inhibit the formation of secondary tumors (metastases) without necessarily affecting the growth of the primary tumor. **Why KAI-1 is correct:** **KAI-1 (CD82)**, located on chromosome 11p11.2, is a member of the tetraspanin family. It promotes cell-cell adhesion and interaction with the extracellular matrix. In **prostate cancer**, the expression of KAI-1 is frequently downregulated or lost as the disease progresses [1]. Its presence prevents the detachment and migration of malignant cells, thereby acting as a specific metastasis suppressor for prostatic adenocarcinoma. **Analysis of Incorrect Options:** * **NM 23:** While this was the first metastasis suppressor gene discovered, it is most classically associated with **breast cancer** and melanoma, rather than being the primary marker for prostate cancer. * **KISS (KiSS-1):** This gene encodes the protein kisspeptin. It is a potent metastasis suppressor primarily associated with **malignant melanoma** and breast cancer. * **p53:** This is a classic **Tumor Suppressor Gene (TSG)**, often called the "Guardian of the Genome." It regulates the cell cycle, DNA repair, and apoptosis [4]. While its loss contributes to cancer progression, it is not classified specifically as a "metastasis suppressor gene." **High-Yield Clinical Pearls for NEET-PG:** * **KAI-1** = Prostate Cancer. * **NM 23** = Breast Cancer / Melanoma. * **BRMS1** = Breast Cancer Metastasis Suppressor 1. * **MKK4** = Ovarian Cancer. * **E-Cadherin (CDH1):** Loss of E-cadherin is a hallmark of **Epithelial-Mesenchymal Transition (EMT)**, a critical step in metastasis across various carcinomas [2], [3]. **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. 993-994. [2] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Neoplasia, pp. 305-306. [3] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Neoplasia, pp. 317-318. [4] Cross SS. Underwood's Pathology: A Clinical Approach. 6th ed. (Basic Pathology) introduces the student to key general principles of pathology, both as a medical science and as a clinical activity with a vital role in patient care. Part 2 (Disease Mechanisms) provides fundamental knowledge about the cellular and molecular processes involved in diseases, providing the rationale for their treatment. Part 3 (Systematic Pathology) deals in detail with specific diseases, with emphasis on the clinically important aspects., pp. 227-228.

Question 403: Arrange the following steps in oncogenesis in the correct sequence:

A. increased activity of telomerase, angiogenesis, Evasion of host defense, Activation of proto-oncogene, Warburg effect
B. Activation of proto-oncogene, Warburg effect, increased activity of telomerase, angiogenesis, Evasion of host defense (Correct Answer)
C. increased activity of telomerase, angiogenesis, Evasion of host defense, Activation of proto-oncogene, Warburg effect
D. Activation of proto-oncogene, Warburg effect, Evasion of host defense, angiogenesis, increased activity of telomerase

Explanation: ### Explanation The process of oncogenesis follows a logical progression of molecular and metabolic changes that allow a normal cell to transform into a malignant tumor. **1. Why Option B is Correct:** The sequence reflects the **Hallmarks of Cancer** as described by Hanahan and Weinberg [1]: * **Activation of proto-oncogenes:** This is the initiating step where genetic mutations (e.g., *RAS*, *MYC*) drive autonomous cell growth [1], [2]. * **Warburg effect:** Early in transformation, rapidly dividing cells switch to aerobic glycolysis to provide metabolic intermediates for synthesizing cellular components [1]. * **Increased activity of telomerase:** To achieve replicative immortality and avoid "mitotic catastrophe," cells must upregulate telomerase to maintain chromosomal length. * **Angiogenesis:** As the tumor mass grows beyond 1-2 mm, it requires its own blood supply (via VEGF) to overcome nutrient and oxygen diffusion limits. * **Evasion of host defense:** Finally, to survive and metastasize, the tumor must develop mechanisms to bypass immune surveillance (e.g., downregulating MHC-I or expressing PD-L1). **2. Why Other Options are Incorrect:** * **Options A & C:** These incorrectly place telomerase activity and angiogenesis before the primary genetic driver (proto-oncogene activation). A cell cannot undergo telomere maintenance or induce angiogenesis without first being triggered into a proliferative state. * **Option D:** This suggests that immune evasion occurs before angiogenesis. In the natural history of tumor progression, a tumor typically establishes a vascular supply to sustain its growth before it reaches a size and complexity that necessitates advanced immune evasion for systemic survival [2]. **3. NEET-PG High-Yield Pearls:** * **Warburg Effect:** Defined as glucose uptake and fermentation to lactate even in the presence of oxygen [1]. It is the basis for **PET scans** (using FDG, a glucose analog). * **Telomerase:** Found in >90% of human cancers; it is absent in most somatic cells but present in germ cells and stem cells. * **Angiogenic Switch:** The transition from a dormant to a growing state, primarily mediated by **VEGF** and **bFGF**. * **Guardian of the Genome:** **TP53** is the most commonly mutated gene in human cancer, acting as a critical checkpoint before these steps can proceed unchecked. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Neoplasia, pp. 290-291. [2] Cross SS. Underwood's Pathology: A Clinical Approach. 6th ed. (Basic Pathology) introduces the student to key general principles of pathology, both as a medical science and as a clinical activity with a vital role in patient care. Part 2 (Disease Mechanisms) provides fundamental knowledge about the cellular and molecular processes involved in diseases, providing the rationale for their treatment. Part 3 (Systematic Pathology) deals in detail with specific diseases, with emphasis on the clinically important aspects., pp. 224-225.

Question 404: What is the major contributor to cachexia in advanced cancer?

A. Clathrin
B. Histamine
C. Interferon
D. Tumor-necrosis-factor (Correct Answer)

Explanation: **Explanation:** **Cancer Cachexia** is a hypermetabolic state characterized by the progressive loss of body fat and lean muscle mass, accompanied by profound weakness, anorexia, and anemia [1]. Unlike simple starvation, it cannot be reversed by increased caloric intake. **Why Tumor Necrosis Factor (TNF) is the correct answer:** TNF (specifically TNF-alpha), formerly known as **cachectin**, is the primary mediator of this process. It is produced by macrophages in response to tumor cells or by the tumor cells themselves. TNF contributes to cachexia through several mechanisms: 1. **Appetite Suppression:** It acts on the hypothalamus to suppress the appetite-regulating signals. 2. **Lipolysis:** It inhibits lipoprotein lipase (LPL), preventing the storage of triglycerides in adipose tissue. 3. **Muscle Proteolysis:** It activates the **ubiquitin-proteasome pathway**, leading to the degradation of skeletal muscle proteins. **Analysis of Incorrect Options:** * **A. Clathrin:** A protein involved in the formation of coated vesicles for receptor-mediated endocytosis; it has no role in systemic metabolic wasting. * **B. Histamine:** A vasoactive amine involved in acute inflammation and type I hypersensitivity; it does not cause chronic muscle or fat wasting. * **C. Interferon:** While Interferon-gamma (IFN-γ) can synergize with TNF to promote wasting, TNF remains the "major" and most characteristic contributor cited in standard pathology (Robbins). **High-Yield Clinical Pearls for NEET-PG:** * **Other Mediators:** Besides TNF, **Interleukin-1 (IL-1)** and **Interleukin-6 (IL-6)** also play significant roles in cachexia. * **PIF (Proteolysis Inducing Factor):** A tumor-derived glycosylated protein that specifically triggers skeletal muscle breakdown. * **LMF (Lipid Mobilizing Factor):** Increases the fatty acid oxidation process. * **Basal Metabolic Rate (BMR):** In cachexia, the BMR is typically **increased**, despite reduced food intake (distinguishing it from starvation where BMR decreases). **References:** [1] Cross SS. Underwood's Pathology: A Clinical Approach. 6th ed. (Basic Pathology) introduces the student to key general principles of pathology, both as a medical science and as a clinical activity with a vital role in patient care. Part 2 (Disease Mechanisms) provides fundamental knowledge about the cellular and molecular processes involved in diseases, providing the rationale for their treatment. Part 3 (Systematic Pathology) deals in detail with specific diseases, with emphasis on the clinically important aspects., pp. 235-236.

Question 405: Which of the following statements regarding the PTEN gene is NOT true?

A. It is a membrane-associated phosphatase.
B. It is encoded by a gene located on chromosome 10q23.
C. It is frequently mutated in endometrial, breast, and thyroid carcinomas.
D. It acts as a proto-oncogene. (Correct Answer)

Explanation: **Explanation:** The **PTEN** (*Phosphatase and Tensin homolog*) gene is a classic example of a **Tumor Suppressor Gene**, not a proto-oncogene [1]. This is the fundamental reason why Option D is the correct answer (the "NOT true" statement). **1. Why Option D is the correct answer:** PTEN acts as a "brake" on cell proliferation [1]. It functions as a lipid phosphatase that antagonizes the **PI3K/AKT signaling pathway** by dephosphorylating PIP3 into PIP2. When PTEN is lost or mutated, the PI3K pathway becomes constitutively active, leading to unchecked cell growth and survival [1]. Proto-oncogenes, by contrast, promote growth and require "gain-of-function" mutations to cause cancer; PTEN requires "loss-of-function." **2. Analysis of other options:** * **Option A:** PTEN is indeed a **membrane-associated phosphatase**. It localizes to the inner surface of the plasma membrane to interact with its lipid substrates [1]. * **Option B:** The PTEN gene is mapped to **chromosome 10q23**. Deletions of this specific locus are a hallmark of many advanced cancers. * **Option C:** PTEN is one of the most frequently mutated genes in human cancer [1]. It is particularly associated with **endometrial carcinoma** (most common mutation), **prostate cancer**, **breast cancer**, and **glioblastomas**. [1]. **High-Yield Clinical Pearls for NEET-PG:** * **Cowden Syndrome:** A germline mutation in PTEN leads to this autosomal dominant disorder characterized by multiple hamartomas and an increased risk of breast, thyroid (follicular), and endometrial cancers. * **Lhermitte-Duclos disease:** A rare cerebellar dysplastic gangliocytoma associated with PTEN mutations. * **Pathway:** PTEN $\rightarrow$ inhibits PIP3 $\rightarrow$ inhibits AKT (Protein Kinase B) $\rightarrow$ inhibits mTOR [1]. Loss of PTEN = Overactive mTOR. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Neoplasia, pp. 294-295.

Question 406: Which of the following is the most chemoresistant tumor?

A. Synovial sarcoma
B. Osteosarcoma
C. Malignant fibrous histiocytoma (Correct Answer)
D. Embryonal rhabdomyosarcoma

Explanation: **Explanation:** The correct answer is **Malignant Fibrous Histiocytoma (MFH)**, now more commonly reclassified as **Pleomorphic Undifferentiated Sarcoma (PUS)**. **1. Why MFH is the correct answer:** Chemosensitivity in tumors is often linked to the degree of cellular differentiation and the proliferative index. MFH is a high-grade, pleomorphic sarcoma characterized by extreme genetic instability and a lack of a specific line of differentiation. Unlike many other soft tissue sarcomas, MFH/PUS is notoriously **chemoresistant** [1]. The primary treatment modality is radical surgical excision; chemotherapy is generally palliative or used with limited success in neoadjuvant settings because these cells possess robust mechanisms to evade drug-induced apoptosis. **2. Why the other options are incorrect:** * **Embryonal Rhabdomyosarcoma:** This is highly **chemosensitive** [3]. It is a "small round blue cell tumor" of childhood. The introduction of the VAC regimen (Vincristine, Actinomycin D, Cyclophosphamide) has dramatically improved survival rates. * **Osteosarcoma:** While aggressive, it is considered **chemosensitive** [1]. Neoadjuvant chemotherapy (e.g., Methotrexate, Doxorubicin, Cisplatin) is the standard of care to shrink the tumor and treat micrometastases before surgery. * **Synovial Sarcoma:** This tumor shows **intermediate sensitivity** to chemotherapy (particularly Ifosfamide-based regimens) [2]. While not as sensitive as Rhabdomyosarcoma, it responds significantly better than MFH. **High-Yield Clinical Pearls for NEET-PG:** * **Most common soft tissue sarcoma in adults:** Historically MFH (now Pleomorphic Undifferentiated Sarcoma). * **Most common soft tissue sarcoma in children:** Rhabdomyosarcoma. * **Small Round Blue Cell Tumors:** (Ewing’s, Lymphoma, Rhabdomyosarcoma, Neuroblastoma) are generally **highly radiosensitive and chemosensitive**. * **Storiform-pleomorphic pattern:** The classic histological description for MFH. **References:** [1] Cross SS. Underwood's Pathology: A Clinical Approach. 6th ed. Common Clinical Problems From Osteoarticular And Connective Tissue Disease, pp. 673-674. [2] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Bones, Joints, and Soft Tissue Tumors, pp. 1225-1226. [3] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Bones, Joints, and Soft Tissue Tumors, pp. 1224-1225.

Question 407: A 55-year-old man presents with a solitary breast mass, and biopsy reveals malignant cells. Immunohistochemical staining shows that the tumor cells are positive for estrogen receptor (ER) and negative for Her2/neu. What is the most likely diagnosis?

A. Basal cell carcinoma
B. Invasive ductal carcinoma (Correct Answer)
C. Medullary carcinoma
D. Tubular adenoma

Explanation: ### Explanation **Correct Answer: B. Invasive ductal carcinoma** **1. Why it is correct:** Invasive Ductal Carcinoma (IDC), specifically the "No Special Type" (NST), is the most common histological subtype of breast cancer in both men and women [1]. In males, breast cancer is almost exclusively ductal because the male breast lacks lobules. The immunohistochemical profile provided (**ER positive, Her2/neu negative**) corresponds to the **Luminal A** molecular subtype, which is the most frequent profile seen in male breast cancer [1]. The age of presentation (55 years) and the solitary nature of the mass are classic clinical features of IDC. **2. Why the other options are incorrect:** * **A. Basal cell carcinoma:** This is a common skin cancer but does not arise from breast parenchyma. While it can occur on the skin of the chest/nipple, it would not be described as a "breast mass" with ER positivity. * **C. Medullary carcinoma:** This is a rare subtype of IDC characterized by "triple negativity" (ER, PR, and Her2/neu negative) and a prominent lymphocytic infiltrate [2]. It is often associated with BRCA1 mutations, which are less common in males than BRCA2. * **D. Tubular adenoma:** This is a benign "pure" epithelial tumor of the breast, typically seen in young women. It would not show "malignant cells" on biopsy. **3. NEET-PG High-Yield Pearls:** * **Male Breast Cancer:** Most commonly associated with **BRCA2 mutations** (more so than BRCA1). Klinefelter syndrome is the strongest risk factor. * **Most Common Site:** The most common location for breast cancer is the **Upper Outer Quadrant**. * **Molecular Subtyping:** * *Luminal A:* ER+, PR+, Her2- (Best prognosis) [1]. * *Luminal B:* ER+, PR+/-, Her2+ (Higher grade than Luminal A). * *Her2 Enriched:* ER-, PR-, Her2+. * *Basal-like (Triple Negative):* ER-, PR-, Her2- (Worst prognosis; associated with BRCA1). **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. The Breast, pp. 1059-1068. [2] Cross SS. Underwood's Pathology: A Clinical Approach. 6th ed. Common Clinical Problems From Liver And Biliary System Disease, pp. 455-456.

Question 408: Which of the following is NOT an oncogenic virus?

A. Hepatitis B virus (HBV)
B. Human papillomavirus (HPV)
C. Epstein-Barr virus (EBV)
D. Varicella-zoster virus (VZV) (Correct Answer)

Explanation: **Explanation:** The correct answer is **Varicella-zoster virus (VZV)**. VZV is a member of the *Alphaherpesvirinae* subfamily and is the causative agent of chickenpox (primary infection) and herpes zoster/shingles (reactivation) [1]. Unlike oncogenic viruses, VZV does not possess mechanisms to integrate into the host genome or dysregulate the cell cycle to promote malignant transformation. **Analysis of Options:** * **Hepatitis B Virus (HBV):** A DNA virus linked to **Hepatocellular Carcinoma (HCC)** [2]. It promotes oncogenesis through chronic inflammation, hepatocyte regeneration, and the HBx protein, which inactivates p53 [5]. * **Human Papillomavirus (HPV):** High-risk types (16, 18) are major causes of **Cervical and Oropharyngeal cancers** [2]. The E6 protein degrades p53, while the E7 protein binds and inactivates the Retinoblastoma (Rb) protein [4]. * **Epstein-Barr Virus (EBV):** A potent oncogenic virus associated with **Burkitt lymphoma, Nasopharyngeal carcinoma, and Hodgkin lymphoma** [2]. It utilizes the LMP-1 protein to mimic CD40 signaling, promoting B-cell proliferation [3]. **High-Yield Clinical Pearls for NEET-PG:** * **RNA Oncogenic Virus:** Human T-cell Leukemia Virus type 1 (HTLV-1) is the only retrovirus directly linked to human cancer (Adult T-cell leukemia/lymphoma) [2]. * **Hepatitis C (HCV):** Though an RNA virus, it is a major cause of HCC, primarily through chronic inflammation and cirrhosis rather than direct viral integration [5]. * **KSHV/HHV-8:** Associated with Kaposi Sarcoma and Primary Effusion Lymphoma [2]. * **Merkel Cell Polyomavirus:** Linked to Merkel cell carcinoma of the skin. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. The Central Nervous System, pp. 1278-1279. [2] Cross SS. Underwood's Pathology: A Clinical Approach. 6th ed. (Basic Pathology) introduces the student to key general principles of pathology, both as a medical science and as a clinical activity with a vital role in patient care. Part 2 (Disease Mechanisms) provides fundamental knowledge about the cellular and molecular processes involved in diseases, providing the rationale for their treatment. Part 3 (Systematic Pathology) deals in detail with specific diseases, with emphasis on the clinically important aspects., pp. 219-220. [3] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Neoplasia, pp. 335-336. [4] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Neoplasia, pp. 334-335. [5] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Neoplasia, pp. 336-337.

Question 409: Which of the following is not considered a pre-malignant condition at some site?

A. Bronchiectasis (Correct Answer)
B. Cholelithiasis
C. Ulcerative colitis
D. Leukoplakia

Explanation: **Explanation:** The correct answer is **Bronchiectasis**. In pathology, a **pre-malignant (pre-neoplastic) condition** is a clinical state associated with a significantly increased risk of developing cancer [2]. 1. **Why Bronchiectasis is the correct answer:** Bronchiectasis is a chronic, obstructive lung disease characterized by permanent dilation of bronchi due to the destruction of elastic and muscular tissue. While it involves chronic inflammation and squamous metaplasia, it is **not** classically considered a precursor to bronchogenic carcinoma [1]. In contrast, conditions like chronic bronchitis (linked to smoking) carry a much higher neoplastic risk [1]. 2. **Analysis of Incorrect Options:** * **Cholelithiasis (Gallstones):** Chronic irritation of the gallbladder wall by stones leads to chronic cholecystitis [3], which is the most significant risk factor for **Gallbladder Carcinoma** [4]. * **Ulcerative Colitis:** This inflammatory bowel disease involves constant mucosal repair and regeneration. Long-standing disease (especially >10 years) significantly increases the risk of **Colorectal Adenocarcinoma**. * **Leukoplakia:** Defined as a white patch or plaque that cannot be characterized clinically or pathologically as any other disease. It is a classic pre-malignant lesion for **Squamous Cell Carcinoma** of the oral cavity. **High-Yield Clinical Pearls for NEET-PG:** * **Metaplasia vs. Neoplasia:** While metaplasia (e.g., Barrett’s Esophagus) is reversible, it often provides the fertile soil for dysplasia and subsequent malignancy [1]. * **Other Pre-malignant conditions to remember:** Actinic keratosis (Skin), Xeroderma pigmentosum, Cirrhosis of liver (Hepatocellular carcinoma), and Atrophic gastritis (Gastric adenocarcinoma). * **Key Distinction:** A *pre-malignant lesion* is a morphologically altered tissue (e.g., Leukoplakia) [2], whereas a *pre-malignant condition* is a generalized disease state (e.g., Ulcerative Colitis) [2]. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. The Lung, p. 723. [2] Cross SS. Underwood's Pathology: A Clinical Approach. 6th ed. (Basic Pathology) introduces the student to key general principles of pathology, both as a medical science and as a clinical activity with a vital role in patient care. Part 2 (Disease Mechanisms) provides fundamental knowledge about the cellular and molecular processes involved in diseases, providing the rationale for their treatment. Part 3 (Systematic Pathology) deals in detail with specific diseases, with emphasis on the clinically important aspects., pp. 222-223. [3] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Liver and Gallbladder, pp. 884-886. [4] Cross SS. Underwood's Pathology: A Clinical Approach. 6th ed. Common Clinical Problems From Liver And Biliary System Disease, pp. 404-405.

Question 410: All of the following are examples of round cell tumors, except?

A. Neuroblastoma
B. Ewing Sarcoma
C. Non-Hodgkin's lymphoma
D. Osteosarcoma (Correct Answer)

Explanation: **Explanation:** Small round blue cell tumors (SRBCTs) are a group of malignant neoplasms characterized histologically by small, round, undifferentiated cells with high nucleocytoplasmic ratios and intense basophilic staining (due to dense chromatin) [1], [3]. **Why Osteosarcoma is the Correct Answer:** Osteosarcoma is primarily a **spindle cell tumor**, not a round cell tumor. Its hallmark histological feature is the production of **osteoid** (unmineralized bone) by malignant mesenchymal cells [4]. While some variants exist, the classic presentation involves pleomorphic spindle-shaped cells rather than uniform small round cells [4]. **Analysis of Incorrect Options:** * **Neuroblastoma:** A classic pediatric SRBCT derived from primordial neural crest cells. It often shows **Homer-Wright rosettes**. * **Ewing Sarcoma:** A prototypical round cell tumor of the bone/soft tissue characterized by the **t(11;22)** translocation. Cells are PAS-positive due to cytoplasmic glycogen [2]. * **Non-Hodgkin’s Lymphoma (NHL):** Specifically the lymphoblastic and Burkitt subtypes are classic examples of round cell malignancies originating from the lymphoid lineage [3]. **NEET-PG High-Yield Pearls:** * **Differential Diagnosis of SRBCTs:** Remember the mnemonic **"ENWR"** (Ewing’s, Neuroblastoma, Wilms’ tumor, Rhabdomyosarcoma) + Lymphoma and Retinoblastoma [1]. * **IHC Markers:** Use CD45 (LCA) for Lymphoma, CD99 (MIC2) for Ewing Sarcoma, and Desmin for Rhabdomyosarcoma [1]. * **Age Factor:** SRBCTs are significantly more common in the pediatric population, whereas spindle cell sarcomas (like Osteosarcoma) often show a bimodal distribution or occur in older adolescents [3],[4]. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Bones, Joints, and Soft Tissue Tumors, pp. 1224-1225. [2] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Bones, Joints, and Soft Tissue Tumors, pp. 1204-1205. [3] Cross SS. Underwood's Pathology: A Clinical Approach. 6th ed. Common Clinical Problems From Diseases Of The Urinary And Male Genital Tracts, pp. 560-561. [4] Cross SS. Underwood's Pathology: A Clinical Approach. 6th ed. Common Clinical Problems From Osteoarticular And Connective Tissue Disease, pp. 673-674.

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