Endocrine Pathology — MCQs

A 45-year-old woman presents with a severe sore throat. Physical examination reveals fever and an extremely tender, enlarged thyroid gland, with no throat erythema. Serum thyroid studies demonstrate mild hyperthyroidism. Two months later, the patient is asymptomatic, and thyroid function tests have returned to normal. She never again experiences difficulty with her thyroid function. Which of the following was the most likely cause of her hyperthyroidism?

Q200Medium

Which is the most common gene mutation responsible for papillary thyroid cancer?

Endocrine Pathology Indian Medical PG Practice Questions and MCQs

Question 191: In which of the following is medullary thyroid cancer the most aggressive form?

A. Multiple Endocrine Neoplasia type I (MEN I)
B. Multiple Endocrine Neoplasia type IIa (MEN IIa)
C. Multiple Endocrine Neoplasia type IIb (MEN IIb) (Correct Answer)
D. Sporadic medullary thyroid cancer cases

Explanation: **Explanation:** Medullary Thyroid Carcinoma (MTC) is a neuroendocrine tumor derived from the parafollicular C-cells of the thyroid [3]. While 75% of cases are sporadic, 25% occur as part of hereditary syndromes due to germline mutations in the **RET proto-oncogene** [1]. **Why Option C is correct:** **MEN IIb** (also known as MEN III) is characterized by the most aggressive clinical course of MTC [1]. In MEN IIb, MTC typically develops in early childhood (often before age 5), is multifocal, and has a high propensity for early metastasis. Due to this extreme virulence, prophylactic thyroidectomy is recommended within the first year of life for infants identified with the associated RET mutation (codon 918). **Why other options are incorrect:** * **Option A (MEN I):** This syndrome (Wermer syndrome) involves the "3 Ps"—Pituitary, Parathyroid, and Pancreatic tumors [2]. It is **not** associated with Medullary Thyroid Cancer. * **Option B (MEN IIa):** While MTC is a hallmark of MEN IIa (Sipple syndrome), it generally appears later in life (teens or young adulthood) and follows a more indolent course compared to MEN IIb [1]. * **Option D (Sporadic MTC):** These usually present as solitary nodules in the 40s–50s. While they can be aggressive, they lack the early onset and rapid progression seen in the hereditary MEN IIb variant. **High-Yield Clinical Pearls for NEET-PG:** * **Biomarker:** Serum **Calcitonin** is used for diagnosis and monitoring recurrence [3]. Amyloid stroma (procalcitonin) is a classic histological finding. * **MEN IIb Phenotype:** Look for "Marfanoid habitus" and mucosal neuromas (tongue/lips) in the clinical stem [1]. * **Genetics:** MEN IIa and IIb are both caused by **RET** mutations, but the specific codons differ, dictating the aggressiveness [1]. * **Rule of 10s:** MTC is associated with MEN syndromes, but always screen for **Pheochromocytoma** before surgery to prevent a hypertensive crisis [1]. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. The Endocrine System, p. 1137. [2] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. The Endocrine System, pp. 1139-1140. [3] Cross SS. Underwood's Pathology: A Clinical Approach. 6th ed. Common Clinical Problems From Liver And Biliary System Disease, pp. 428-429.

Question 192: Which of the following is characteristic of Hashimoto's thyroiditis?

A. Follicular destruction
B. Increase in lymphocytes
C. Oncocytic metaplasia
D. Orphan Annie eye nuclei (Correct Answer)

Explanation: ### Explanation The correct answer is **D. Orphan Annie eye nuclei**. **Note on the Question:** There appears to be a discrepancy in the provided key. **Orphan Annie eye nuclei** are the pathognomonic hallmark of **Papillary Thyroid Carcinoma (PTC)**, not Hashimoto’s thyroiditis [1]. In Hashimoto’s thyroiditis, the classic features are follicular destruction, dense lymphocytic infiltration, and Hurthle cell (oncocytic) metaplasia. If this question appeared in a NEET-PG context with "D" as the marked correct answer, it likely represents a "recall error" or a specific focus on the association between Hashimoto’s and the increased risk of developing Papillary Carcinoma. #### Why the options are significant: * **Orphan Annie eye nuclei (Correct per key):** These are large, clear, "ground-glass" nuclei seen in Papillary Thyroid Carcinoma [1]. While not a primary feature of Hashimoto’s, patients with Hashimoto’s have a significantly higher risk (approx. 3x) of developing PTC. * **Follicular destruction (A):** This is a primary feature of Hashimoto’s. The autoimmune process (anti-TPO and anti-thyroglobulin antibodies) leads to the progressive destruction of thyroid follicles [2, 3]. * **Increase in lymphocytes (B):** Hashimoto’s is characterized by a dense inflammatory infiltrate consisting of lymphocytes and plasma cells, often forming **germinal centers** [2, 3]. * **Oncocytic metaplasia (C):** Also known as **Hurthle cells** or Askanazy cells. These are follicular epithelial cells with abundant, granular, eosinophilic cytoplasm due to mitochondrial stress [2]. #### NEET-PG High-Yield Pearls: * **Hashimoto’s Triad:** Lymphocytic infiltrate + Germinal centers + Hurthle cells [2]. * **Most common cause** of hypothyroidism in iodine-sufficient regions [3]. * **HLA Association:** HLA-DR3 and HLA-DR5. * **Malignancy Risk:** Hashimoto’s increases the risk of **B-cell Non-Hodgkin Lymphoma** (specifically MALToma) and Papillary Thyroid Carcinoma [2]. * **Antibodies:** Anti-TPO (most sensitive) and Anti-Thyroglobulin. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. The Endocrine System, p. 1099. [2] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. The Endocrine System, pp. 1090-1091. [3] Cross SS. Underwood's Pathology: A Clinical Approach. 6th ed. Common Clinical Problems From Liver And Biliary System Disease, pp. 427-428.

Question 193: In Hashimoto's thyroiditis, what type of cells infiltrate the thyroid gland?

A. Macrophages
B. Neutrophils
C. Leukocytes (Correct Answer)
D. Eosinophils

Explanation: **Explanation:** **Hashimoto’s Thyroiditis** (Chronic Lymphocytic Thyroiditis) is an autoimmune disorder characterized by the destruction of thyroid follicles by the immune system [1]. The hallmark of this condition is a dense **mononuclear inflammatory infiltrate** within the thyroid parenchyma [1]. **Why "Leukocytes" is the correct answer:** In medical terminology, "leukocytes" is a broad category encompassing all white blood cells [4]. Specifically, Hashimoto’s is defined by a massive infiltration of **lymphocytes** (T-cells and B-cells) and **plasma cells** [1]. These lymphocytes often organize into well-developed **germinal centers**, mimicking the architecture of a lymph node [2]. Since lymphocytes are a type of leukocyte, this option represents the primary cellular component of the disease pathology. **Analysis of Incorrect Options:** * **A. Macrophages:** While macrophages may be present to clear debris, they are not the defining or predominant cell type of the infiltrate. * **B. Neutrophils:** These are markers of acute inflammation (e.g., infectious thyroiditis). Hashimoto’s is a chronic, autoimmune process [4]. * **D. Eosinophils:** These are typically associated with allergic reactions or parasitic infections and do not play a primary role in Hashimoto’s [2]. **High-Yield Clinical Pearls for NEET-PG:** * **Hürthle Cells (Askanazy cells):** These are follicular epithelial cells that undergo metaplasia, appearing enlarged with granular, eosinophilic cytoplasm due to mitochondrial stress. * **Antibodies:** Most patients are positive for **Anti-TPO** (Thyroid Peroxidase) and **Anti-Thyroglobulin** antibodies. * **HLA Association:** Strongly linked with **HLA-DR3** and **HLA-DR5**. * **Risk of Malignancy:** Patients have an increased risk of developing **B-cell Non-Hodgkin Lymphoma** (specifically MALToma) and Papillary Thyroid Carcinoma [3]. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. The Endocrine System, pp. 1089-1090. [2] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Inflammation and Repair, pp. 107-109. [3] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Diseases of the Immune System, pp. 235-236. [4] Cross SS. Underwood's Pathology: A Clinical Approach. 6th ed. Common Clinical Problems From Blood And Bone Marrow Disease, pp. 579-580.

Question 194: Gs alpha mutation is associated with all of the following except?

A. McCune-Albright syndrome
B. Pituitary adenomas
C. Pseudohypoparathyroidism
D. Papillary carcinoma thyroid (Correct Answer)

Explanation: **Explanation:** The **Gsα (GNAS1 gene)** mutation leads to the constitutive activation of adenylate cyclase, resulting in the overproduction of cAMP. This pathway acts as a potent mitogen in several endocrine tissues. **Why Papillary Carcinoma Thyroid (PTC) is the correct answer:** Papillary carcinoma of the thyroid is primarily associated with mutations in the **MAPK pathway**, most commonly the **BRAF V600E mutation** (found in ~60% of cases) or **RET/PTC rearrangements**. Gsα mutations are not a feature of PTC. **Analysis of Incorrect Options:** * **McCune-Albright Syndrome:** Caused by a **post-zygotic somatic mutation** in GNAS1 [1]. It presents with the triad of polyostotic fibrous dysplasia, café-au-lait spots, and autonomous endocrine hyperfunction (e.g., precocious puberty). * **Pituitary Adenomas:** Somatic mutations in Gsα (specifically the **gsp oncogene**) are found in approximately 40% of **Somatotroph (GH-secreting) adenomas** [1]. The mutation mimics the action of GHRH, leading to persistent GH secretion. * **Pseudohypoparathyroidism (PHP):** Specifically Type 1a (Albright’s Hereditary Osteodystrophy), which involves an **inactivating mutation** of the Gsα protein. This leads to end-organ resistance to PTH, resulting in hypocalcemia and hyperphosphatemia despite elevated PTH levels. **High-Yield Clinical Pearls for NEET-PG:** * **GNAS1 Mutation:** If *activating*, it leads to McCune-Albright or Pituitary adenomas [1]. If *inactivating*, it leads to Pseudohypoparathyroidism. * **Follicular Thyroid Carcinoma:** Associated with **RAS mutations** or **PAX8-PPARG** translocations. * **Medullary Thyroid Carcinoma:** Associated with **RET proto-oncogene** mutations (MEN 2A/2B). **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. The Endocrine System, pp. 1079-1081.

Question 195: Calcitonin is a marker of which of the following?

A. Pancreatic cancer
B. Lobular carcinoma of the breast
C. Melanoma
D. Carcinoma of the thyroid (Correct Answer)

Explanation: **Explanation:** **Correct Answer: D. Carcinoma of the thyroid** Calcitonin is a 32-amino acid hormone produced by the **Parafollicular cells (C-cells)** of the thyroid gland [2]. Its primary physiological role is to lower blood calcium levels by inhibiting osteoclast activity [4]. In pathology, Calcitonin serves as a highly specific and sensitive tumor marker for **Medullary Thyroid Carcinoma (MTC)**, which arises from these C-cells [2]. It is used for diagnosis, monitoring treatment response, and detecting recurrence. **Analysis of Incorrect Options:** * **A. Pancreatic cancer:** The primary markers for pancreatic adenocarcinoma are **CA 19-9** and CEA. While some neuroendocrine tumors of the pancreas may produce ectopic hormones, Calcitonin is not a standard marker. * **B. Lobular carcinoma of the breast:** The markers for breast cancer include **ER/PR, HER2/neu**, and **CA 15-3**. Lobular carcinoma is specifically associated with a loss of **E-cadherin** expression. * **C. Melanoma:** Key immunohistochemical markers for melanoma include **S-100, HMB-45, and Melan-A**. **NEET-PG High-Yield Pearls:** * **Amyloid Stroma:** Medullary Thyroid Carcinoma is histologically characterized by nests of tumor cells in a prominent **amyloid stroma** (formed by pro-calcitonin fibrils) [3], which stains with **Congo Red** (apple-green birefringence). * **Genetics:** Approximately 25% of MTC cases are familial, associated with **RET proto-oncogene** mutations in **MEN 2A and 2B** syndromes [1]. * **CEA:** Carcinoembryonic antigen (CEA) is also often elevated in MTC and is used alongside Calcitonin for prognosis [1]. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. The Endocrine System, pp. 1102-1103. [2] Cross SS. Underwood's Pathology: A Clinical Approach. 6th ed. Common Clinical Problems From Liver And Biliary System Disease, pp. 428-429. [3] Cross SS. Underwood's Pathology: A Clinical Approach. 6th ed. Common Clinical Problems From Liver And Biliary System Disease, pp. 430-431. [4] Cross SS. Underwood's Pathology: A Clinical Approach. 6th ed. Common Clinical Problems From Liver And Biliary System Disease, pp. 431-432.

Question 196: Which of the following features would a thyroid biopsy MOST likely show in Hashimoto's disease?

A. Thyroid follicle destruction and fibrosis by macrophages and giant cells
B. Thyroid follicle destruction by lymphocytes and presence of Hurthle cells (Correct Answer)
C. Thyroid follicles with finger-like growths
D. Thyroid follicles with large colloid and flattened epithelial cells

Explanation: ### **Explanation** **Hashimoto’s Thyroiditis** (Chronic Lymphocytic Thyroiditis) is the most common cause of hypothyroidism in iodine-sufficient regions. It is an autoimmune disorder characterized by the destruction of thyroid follicles by a cell-mediated immune response [1]. #### **1. Why Option B is Correct** The hallmark histological features of Hashimoto’s are: * **Diffuse Lymphocytic Infiltrate:** The thyroid parenchyma is heavily infiltrated by lymphocytes and plasma cells, often forming **well-developed germinal centers** [1]. * **Hurthle Cells (Askanazy Cells):** These are follicular epithelial cells that have undergone metaplasia. They appear enlarged with abundant, granular, **eosinophilic cytoplasm** due to a high concentration of mitochondria [1]. * **Follicular Destruction:** The cytotoxic T-cell-mediated attack leads to the progressive loss of thyroid follicles [1]. #### **2. Why Other Options are Incorrect** * **Option A:** Describes **Subacute Granulomatous (De Quervain) Thyroiditis**. This is characterized by granulomatous inflammation with multinucleated giant cells, typically following a viral infection. * **Option C:** Describes **Papillary Thyroid Carcinoma**, which features papillary (finger-like) projections with fibrovascular cores, or potentially Graves' disease (scalloping of colloid). * **Option D:** Describes a **Colloid Goiter**. In this state, the follicles are distended with abundant colloid and the lining epithelium is flattened/inactive. #### **3. NEET-PG High-Yield Pearls** * **Antibodies:** Anti-TPO (Thyroid Peroxidase) and Anti-Thyroglobulin antibodies are markers of the disease. * **HLA Association:** Strongly associated with **HLA-DR3** and **HLA-DR5**. * **Clinical Sign:** Initially, patients may present with transient hyperthyroidism (**Hashitoxicosis**) due to follicle rupture, followed by permanent hypothyroidism [1]. * **Increased Risk:** Patients have an increased risk of developing **B-cell Non-Hodgkin Lymphoma** (specifically MALT lymphoma) and Papillary Thyroid Carcinoma. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. The Endocrine System, pp. 1089-1091.

Question 197: What feature differentiates follicular carcinoma from follicular adenoma of the thyroid?

A. Nuclear pleomorphism
B. Hürthle cell change
C. Capsular invasion (Correct Answer)
D. Absence of colloid

Explanation: **Explanation:** The differentiation between follicular adenoma and follicular carcinoma is a classic high-yield topic in thyroid pathology. Both lesions present with a similar follicular architecture and lack the characteristic nuclear features of papillary carcinoma. **Why Capsular/Vascular Invasion is Correct:** The definitive diagnosis of **Follicular Thyroid Carcinoma (FTC)** relies exclusively on the demonstration of **capsular invasion** (penetration through the entire thickness of the capsule) or **vascular invasion** (vessels within or outside the capsule) [1]. If the lesion is completely encapsulated without these features, it is classified as a Follicular Adenoma [1]. Therefore, a Fine Needle Aspiration (FNA) cannot distinguish between the two; a formal histological examination of the surgical specimen is mandatory. **Analysis of Incorrect Options:** * **A & D (Nuclear pleomorphism & Absence of colloid):** These features can be seen in both benign and malignant follicular lesions. Cellular atypia and reduced colloid are common in hypercellular adenomas and do not signify malignancy in the thyroid. * **B (Hürthle cell change):** This refers to oncocytic change (cells with granular, eosinophilic cytoplasm). While Hürthle cell variants exist for both adenomas and carcinomas, the presence of these cells alone does not determine malignancy [1]. **NEET-PG High-Yield Pearls:** * **Mode of Spread:** Unlike Papillary carcinoma (lymphatic), Follicular carcinoma spreads primarily via the **hematogenous route** (commonly to bone and lungs) [2]. * **Molecular Pathology:** FTC is frequently associated with **RAS mutations** or the **PAX8-PPARG** fusion gene. * **Cold Nodule:** On scintigraphy, both adenomas and carcinomas typically appear as "cold" nodules. * **Frozen Section:** Generally unreliable for differentiating these two; permanent sections are required to evaluate the capsule thoroughly. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. The Endocrine System, pp. 1096-1101. [2] Cross SS. Underwood's Pathology: A Clinical Approach. 6th ed. Common Clinical Problems From Liver And Biliary System Disease, pp. 428-429.

Question 198: GNAS mutation is associated with malignancy of which of the following pituitary cell types?

A. Lactotrophs
B. Somatotrophs (Correct Answer)
C. Thyrotrophs
D. Corticotrophs

Explanation: ### Explanation **Correct Answer: B. Somatotrophs** **Mechanism and Pathophysiology:** The **GNAS gene** (located on chromosome 20q13) encodes the alpha subunit of the stimulatory G-protein (**Gsα**). In approximately **40% of somatotroph (Growth Hormone-secreting) adenomas**, a gain-of-function mutation occurs in the GNAS gene [1]. This mutation inhibits the GTPase activity of the Gsα subunit, leading to constitutive activation of adenylate cyclase [1]. This results in persistent elevation of intracellular **cAMP**, which acts as a potent mitogenic signal for somatotrophs, driving cellular proliferation and autonomous GH secretion (leading to Gigantism or Acromegaly) [1]. **Analysis of Incorrect Options:** * **A. Lactotrophs:** While prolactinomas are the most common pituitary tumors, they are rarely associated with GNAS mutations [3]. They are more frequently linked to *MEN1* mutations or *AIP* gene alterations. * **C. Thyrotrophs:** TSH-secreting tumors are rare. While they utilize the cAMP pathway, GNAS mutations are not a characteristic primary driver for these specific cells compared to somatotrophs [1]. * **D. Corticotrophs:** ACTH-secreting adenomas (Cushing’s disease) are primarily associated with mutations in the **USP8 gene**, which prevents the degradation of the EGF receptor, rather than GNAS mutations. **High-Yield Clinical Pearls for NEET-PG:** * **McCune-Albright Syndrome:** Characterized by the triad of polyostotic fibrous dysplasia, café-au-lait spots, and precocious puberty. It is caused by a **post-zygotic somatic mutation** in the GNAS gene [2]. * **Somatotroph Adenomas:** These are the second most common type of functioning pituitary adenoma [3]. * **Morphology:** On pathology, GH-secreting tumors are classified into **densely granulated** (strong GH staining) and **sparsely granulated** (weak staining, characterized by "fibrous bodies" on IHC for cytokeratin) [3]. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. The Endocrine System, pp. 1079-1081. [2] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. The Endocrine System, pp. 1126-1127. [3] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. The Endocrine System, p. 1079.

Question 199: A 45-year-old woman presents with a severe sore throat. Physical examination reveals fever and an extremely tender, enlarged thyroid gland, with no throat erythema. Serum thyroid studies demonstrate mild hyperthyroidism. Two months later, the patient is asymptomatic, and thyroid function tests have returned to normal. She never again experiences difficulty with her thyroid function. Which of the following was the most likely cause of her hyperthyroidism?

A. Diffuse nontoxic goiter
B. Graves disease
C. Hashimoto's thyroiditis
D. Subacute granulomatous thyroiditis (Correct Answer)

Explanation: ### Explanation The clinical presentation of a **painful, tender thyroid gland** following a viral prodrome (fever, sore throat) is the classic hallmark of **Subacute Granulomatous Thyroiditis (De Quervain Thyroiditis)** [1][3]. **1. Why the Correct Answer is Right:** Subacute granulomatous thyroiditis is a self-limiting inflammatory condition, often triggered by a viral infection (e.g., Coxsackievirus, Mumps). The inflammation causes the destruction of thyroid follicles, leading to the **leakage of preformed thyroid hormones** into the bloodstream [1]. This results in a transient phase of **hyperthyroidism** (low TSH, high T4). As the hormone stores are depleted, a brief hypothyroid phase may follow, but the condition typically resolves completely within 6–8 weeks, returning the patient to a **euthyroid state** [1]. The hallmark is an **exquisitely tender thyroid** [3] and an elevated Erythrocyte Sedimentation Rate (ESR). **2. Why the Other Options are Wrong:** * **Diffuse nontoxic goiter:** Presents as painless thyroid enlargement without clinical hyperthyroidism or hypothyroidism. * **Graves Disease:** Characterized by painless goiter, exophthalmos, and pretibial myxedema [4]. It is a chronic autoimmune condition caused by TSH-receptor antibodies and does not resolve spontaneously. * **Hashimoto’s Thyroiditis:** While it can cause transient "Hashitoxicosis" [2], it typically presents as a **painless** goiter and eventually leads to permanent hypothyroidism. Histology shows Hurthle cells and lymphoid follicles with germinal centers [2]. **3. NEET-PG High-Yield Pearls:** * **Most common cause of thyroid pain:** Subacute Granulomatous Thyroiditis. * **Key Lab Finding:** Elevated ESR and **low radioactive iodine uptake (RAIU)** (due to follicular damage, not increased synthesis) [1]. * **Histology:** Granulomatous inflammation with **multinucleated giant cells**. * **Treatment:** Usually supportive with NSAIDs or corticosteroids; antithyroid drugs (PTU/Methimazole) are **not** indicated because the hyperthyroidism is due to leakage, not overproduction. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. The Endocrine System, pp. 1091-1092. [2] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. The Endocrine System, pp. 1090-1091. [3] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. The Endocrine System, p. 1087. [4] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. The Endocrine System, pp. 1087-1088.

Question 200: Which is the most common gene mutation responsible for papillary thyroid cancer?

A. RET
B. RAS
C. p53
D. BRAF (Correct Answer)

Explanation: **Explanation:** **Papillary Thyroid Carcinoma (PTC)** is the most common type of thyroid malignancy [2]. The molecular pathogenesis of PTC primarily involves the activation of the **MAP Kinase (MAPK) pathway** [1]. 1. **Why BRAF is correct:** The **BRAF V600E mutation** is the most common genetic alteration in PTC, occurring in approximately **40–50%** of cases. This point mutation leads to constitutive activation of the BRAF kinase, driving uncontrolled cell proliferation. Clinically, BRAF mutations are often associated with specific variants (like the classic and tall-cell variants) and may correlate with a higher risk of lymph node metastasis. 2. **Why other options are incorrect:** * **RET:** While *RET/PTC* rearrangements (translocations) are characteristic of PTC (found in 20–40% of cases), they are less frequent than BRAF mutations [1]. Germline *RET* mutations are specifically associated with Medullary Thyroid Carcinoma (MEN 2A/2B). * **RAS:** Mutations in the *RAS* family are more typical of **Follicular Thyroid Carcinoma** and the follicular variant of PTC, but they are not the most common overall for PTC. * **p53:** Mutations in the *TP53* tumor suppressor gene are rare in well-differentiated thyroid cancers; they are typically markers of progression to **Anaplastic Thyroid Carcinoma** [3]. **High-Yield Clinical Pearls for NEET-PG:** * **Psammoma bodies:** Concentric calcifications highly characteristic of PTC (found in ~50% of cases). * **Nuclear features:** "Orphan Annie eye" nuclei (clearing), nuclear grooves, and pseudo-inclusions are diagnostic hallmarks [3]. * **Risk factor:** Prior exposure to ionizing radiation is the most significant environmental risk factor [2]. * **Prognosis:** Excellent, with a 10-year survival rate >95% [3]. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. The Endocrine System, pp. 1097-1098. [2] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. The Endocrine System, pp. 1098-1099. [3] Cross SS. Underwood's Pathology: A Clinical Approach. 6th ed. Common Clinical Problems From Liver And Biliary System Disease, pp. 429-430.

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