Weekly Pathology Exam - October 9, 2026 (Section A: MCQs) MCQs

Question 1

A 62-year-old woman with Idiopathic Pulmonary Fibrosis (IPF) has worsening dyspnea over 2 weeks without infection. HRCT now shows new bilateral ground-glass opacities superimposed on her existing fibrosis. What is the most likely complication?

Accepted Answer

Acute exacerbation of IPF — New ground-glass opacities in a patient with known IPF, especially with acute worsening dyspnea, are highly suggestive of an acute exacerbation of IPF.

Question 2

Pulmonary function testing in a patient with Idiopathic Pulmonary Fibrosis (IPF) is most likely to show which pattern?

Accepted Answer

Restrictive pattern with decreased DLCO — IPF is a restrictive lung disease characterized by reduced lung volumes and a reduced diffusing capacity for carbon monoxide (DLCO) due to thickened alveolar walls.

Question 3

Which immunohistochemical marker is most useful in distinguishing malignant mesothelioma from metastatic adenocarcinoma to the pleura?

Accepted Answer

WT-1 — WT-1 (Wilms tumor 1) is typically positive in malignant mesothelioma and negative in most metastatic adenocarcinomas. CK7 can be positive in both, CK20 is more characteristic of adenocarcinoma, and TTF-1 is typically positive in lung adenocarcinoma.

Question 4

A 55-year-old man with heart failure has a right-sided pleural effusion. Thoracentesis shows fluid protein of 2.1 g/dL, serum protein 7.0 g/dL, fluid LDH 88 U/L, and serum LDH 300 U/L. What is the most likely type of effusion?

Accepted Answer

Transudative — Using Light's criteria, this is a transudative effusion: Fluid protein/serum protein ratio is 2.1/7.0 = 0.3 ( < 0.5), and fluid LDH/serum LDH ratio is 88/300 = 0.29 (< 0.6). Heart failure is a common cause of transudative effusions.

Question 5

A 48-year-old woman with breast cancer develops a right pleural effusion. Thoracentesis yields fluid protein of 5.2 g/dL, serum protein 6.8 g/dL, fluid LDH 420 U/L, and serum LDH 310 U/L. Cytology shows malignant cells. What is the most likely type of effusion?

Accepted Answer

Malignant — Using Light's criteria, this is an exudative effusion: Fluid protein/serum protein ratio is 5.2/6.8 = 0.76 ( 0.5), and fluid LDH/serum LDH ratio is 420/310 = 1.35 ( 0.6). The presence of malignant cells in the cytology confirms it as a malignant effusion, which is a subtype of exudative effusion.

Question 6

A 35-year-old man undergoes thoracic duct injury during left-sided neck dissection surgery. Two days later he develops a left pleural effusion. Thoracentesis yields milky white fluid with triglycerides of 210 mg/dL. What is the most likely diagnosis?

Accepted Answer

Chylothorax — A milky white pleural effusion with high triglyceride content is characteristic of chylothorax, resulting from leakage of lymphatic fluid from the thoracic duct.

Question 7

A 45-year-old man has a 3-month history of recurrent sinusitis, epistaxis, haemoptysis, and haematuria. CXR shows bilateral cavitating nodules. Urinalysis shows red cell casts. c-ANCA (PR3-ANCA) is strongly positive. What is the most likely diagnosis?

Accepted Answer

Granulomatosis with Polyangiitis (Wegener's) — This constellation of symptoms (sinusitis, hemoptysis, renal involvement with red cell casts) and a positive c-ANCA (PR3-ANCA) is classic for Granulomatosis with Polyangiitis (formerly Wegener's).

Question 8

A 38-year-old woman with asthma develops peripheral blood eosinophilia of 18%, p-ANCA positivity, and a new mononeuritis multiplex. CXR shows transient pulmonary infiltrates. What is the most likely diagnosis?

Accepted Answer

Eosinophilic Granulomatosis with Polyangiitis (Churg-Strauss) — The combination of asthma, peripheral eosinophilia, p-ANCA positivity, mononeuritis multiplex, and transient pulmonary infiltrates is highly suggestive of Eosinophilic Granulomatosis with Polyangiitis (EGPA), formerly known as Churg-Strauss syndrome.

Question 9

A 24-year-old male smoker presents with haemoptysis and progressive dyspnea. Urinalysis shows proteinuria and red cell casts. CXR reveals bilateral alveolar infiltrates. Anti-GBM antibodies are strongly positive. Renal biopsy shows linear IgG deposits along the glomerular basement membrane. What is the most likely diagnosis?

Accepted Answer

Anti-GBM Disease (Goodpasture Syndrome) — The presence of haemoptysis, renal disease with red cell casts, positive anti-GBM antibodies, and linear IgG deposition on renal biopsy is pathognomonic for Anti-GBM Disease, also known as Goodpasture Syndrome when pulmonary and renal involvement are present.

Question 10

A 55-year-old granite quarry worker has 20 years of exposure to silica dust. He now has progressive dyspnea and a dry cough. CXR shows upper lobe predominant nodules with eggshell calcification of hilar lymph nodes. Pulmonary function shows a restrictive pattern. What is the most likely diagnosis?

Accepted Answer

Silicosis — Occupational history of silica exposure, upper lobe predominant nodules, eggshell calcification of hilar lymph nodes, and a restrictive PFT pattern are characteristic features of silicosis.

Question 11

A 32-year-old woman with no cardiopulmonary disease has progressive exertional dyspnea, syncope on exertion, and loud P2 on auscultation. Right heart catheterization shows mean pulmonary artery pressure of 38 mmHg with normal pulmonary capillary wedge pressure. What is the most likely diagnosis?

Accepted Answer

Pulmonary arterial hypertension (PAH) — The combination of exertional dyspnea, syncope, loud P2, elevated pulmonary artery pressure, and normal pulmonary capillary wedge pressure strongly suggests pulmonary arterial hypertension (PAH).

Question 12

A 70-year-old man with severe COPD has increasing drowsiness. ABG shows pH 7.28, PaO2 55 mmHg, PaCO2 72 mmHg, and HCO3 32 mEq/L. What is the most likely type of respiratory failure?

Accepted Answer

Type II (hypercapnic) — This ABG demonstrates respiratory acidosis (pH 7.28) with significant hypercapnia (PaCO2 72 mmHg) and hypoxemia (PaO2 55 mmHg). This is characteristic of Type II respiratory failure, often seen in severe COPD due to alveolar hypoventilation.

Question 13

A 63-year-old woman has sudden 'knife-like' chest pain radiating to the back, poorly controlled hypertension, and a widened mediastinum on CXR. CK is normal. What is the most likely diagnosis?

Accepted Answer

Aortic dissection — Sudden, severe, tearing chest pain radiating to the back, a history of hypertension, and a widened mediastinum on CXR are classic signs of aortic dissection. Normal CK rules out acute MI.

Question 14

A man is examined 4 days after a large transmural anterolateral MI with cardiogenic shock. What is the most likely microscopic finding in the affected myocardium?

Accepted Answer

Extensive coagulative necrosis with established granulation tissue formation — At 4 days post-MI, the necrotic myocardium would be well-established with significant neutrophil infiltration and the early stages of granulation tissue formation at the edges of the infarct.

Question 15

A 45-year-old woman has orthopnea, dysphagia, and a prior stroke. CXR shows near-normal LV but prominent left atrial border. What is the most likely condition?

Accepted Answer

Mitral stenosis — A prominent left atrial border on CXR is indicative of left atrial enlargement. In the context of orthopnea and dysphagia (potentially due to enlarged left atrium pressing on the esophagus), mitral stenosis is a strong possibility, leading to left atrial dilation.

Question 16

A 16-year-old is stabbed in the left chest. BP barely obtainable, lungs clear, heart sounds barely audible. What is the most useful treatment?

Accepted Answer

Tube thoracostomy — The patient's hemodynamic instability (barely obtainable BP) and clear lungs with faint heart sounds after chest trauma strongly suggest cardiac tamponade. Tube thoracostomy is indicated to drain the pericardial space.

Question 17

A 19-year-old with mid-systolic click, mitral insufficiency, aortic root dilation, and a dislocated lens dies suddenly. Ruptured chordae found at autopsy. What is the most likely gene mutation?

Accepted Answer

FBN1 — This constellation of findings (mitral valve prolapse with click, aortic root dilation, dislocated lens, and ruptured chordae) is highly suggestive of Marfan syndrome, which is caused by mutations in the FBN1 gene encoding fibrillin-1.

Question 18

A 72-year-old woman with no prior illness has three syncopal episodes then pulmonary edema. CXR shows LV prominence only. Cholesterol normal. What is the most likely diagnosis?

Accepted Answer

Aortic stenosis — Severe aortic stenosis can present with syncope and heart failure (pulmonary edema). The LV prominence on CXR can be a sign of pressure overload. Normal cholesterol makes other causes less likely.

Question 19

A 17-year-old short girl with absent puberty, webbed neck, upper extremity hypertension, diminished lower extremity pulses, and rib notching on CXR. What is the most likely cardiovascular abnormality?

Accepted Answer

Coarctation of the aorta — This patient's presentation is highly suggestive of Turner syndrome (XO karyotype), which is frequently associated with coarctation of the aorta, characterized by upper extremity hypertension and diminished lower extremity pulses. Rib notching on CXR is a classic finding of coarctation due to collateral flow through intercostal arteries.

Question 20

A 65-year-old man with 20 years of uncontrolled diabetes has sudden severe abdominal pain, diminished lower-extremity pulses, and a pulsatile abdominal mass. CK normal. What is the most likely condition?

Accepted Answer

Ruptured abdominal aortic aneurysm — A pulsatile abdominal mass, severe abdominal pain, and diminished lower extremity pulses in a patient with risk factors like uncontrolled diabetes and hypertension strongly suggest a ruptured abdominal aortic aneurysm (AAA). Normal CK excludes acute MI.

Question 21

A 49-year-old woman with poorly controlled atrial fibrillation dies after a stroke. Autopsy shows fused mitral leaflets, shortened chordae, and thrombus-filled enlarged left atrium. What is the most likely underlying cause?

Accepted Answer

Rheumatic heart disease — The findings of fused mitral leaflets, shortened chordae, left atrial enlargement, and thrombus formation are highly characteristic of chronic rheumatic heart disease, a sequela of rheumatic fever, which predisposes to atrial fibrillation and thromboembolic events.

Question 22

A 23-year-old woman with a malar rash has a friction rub, a faint systolic murmur, small mitral vegetations on echo, and a very high anti-Smith antibody titer. What is the most likely diagnosis?

Accepted Answer

Systemic Lupus Erythematosus (SLE) with Libman-Sacks endocarditis — The combination of malar rash, friction rub (pericarditis is common in SLE), valvular vegetations (Libman-Sacks endocarditis is characteristic of SLE), and high anti-Smith antibody titers is diagnostic of Systemic Lupus Erythematosus (SLE).

Question 23

A fetus at 18 weeks has a VSD, overriding aorta, and marked pulmonic atresia. If liveborn, what physical finding would most likely result?

Accepted Answer

Cyanosis — This combination of defects (VSD, overriding aorta, pulmonic atresia) describes a form of Tetralogy of Fallot with atresia. With marked pulmonic atresia, pulmonary blood flow will be dependent on the VSD and patent ductus arteriosus, leading to significant cyanosis if not corrected.

Question 24

A 50-year-old man has 3 hours of substernal chest pain, ST elevation in V1–V6, and pulmonary edema. Which lab finding is most likely?

Accepted Answer

All of the above — ST-elevation myocardial infarction (STEMI) in the anterior leads (V1-V6) indicates extensive myocardial damage. Elevated Troponin I and CK-MB are specific markers of myocardial injury. Pulmonary edema indicates heart failure secondary to the MI, leading to elevated BNP.

Question 25

A 52-year-old woman undergoes thyroidectomy for a well-circumscribed, encapsulated thyroid nodule. Histology shows uniform follicles resembling normal thyroid architecture. Which of the following is the most accurate designation?

Accepted Answer

Follicular adenoma — A well-circumscribed, encapsulated nodule with uniform follicles resembling normal thyroid architecture, without capsular or vascular invasion, is characteristic of a benign follicular adenoma. The key to distinguishing follicular adenoma from carcinoma is the presence of invasion.

Question 26

A 65-year-old man presents with a firm mass in the sigmoid colon. Colonoscopy shows an ulcerated lesion with irregular borders. Biopsy demonstrates invasion through the muscularis propria. Which histological feature most strongly distinguishes this lesion as malignant rather than benign?

Accepted Answer

Nuclear pleomorphism — Nuclear pleomorphism (variation in nuclear size and shape) and hyperchromasia are hallmark features of malignancy and are crucial in distinguishing malignant from benign lesions, even when other architectural features are present.

Question 27

A 45-year-old woman develops chronic myeloid leukemia (CML). Cytogenetic analysis reveals a reciprocal translocation between chromosomes 9 and 22. The resultant fusion gene codes for a protein with which abnormal activity?

Accepted Answer

Constitutively active tyrosine kinase — The t(9;22) translocation in CML creates the Philadelphia chromosome, resulting in the BCR-ABL fusion gene. This fusion gene encodes a constitutively active tyrosine kinase that drives uncontrolled cell proliferation.

Question 28

A 33-year-old woman with breast cancer is found to have HER2/neu gene amplification. Which of the following best describes the mechanism by which HER2/neu promotes oncogenesis?

Accepted Answer

It is a receptor tyrosine kinase that stimulates downstream signaling pathways involved in cell proliferation and survival. — HER2/neu (ERBB2) is a receptor tyrosine kinase. Amplification leads to increased expression and constitutive activation, which drives downstream signaling pathways (e.g., PI3K/Akt, MAPK) promoting cell growth, survival, and angiogenesis, contributing to oncogenesis.

Question 29

A 28-year-old man presents with bilateral retinoblastomas. Genetic analysis reveals a germline mutation in one allele of the RB gene, followed by somatic loss of the second allele. This exemplifies which principle?

Accepted Answer

Two-hit hypothesis — The development of retinoblastoma in this scenario, where a germline mutation in one allele of the RB1 tumor suppressor gene is followed by a somatic mutation of the other allele, is a classic example of the 'two-hit hypothesis' proposed by Knudson.

Question 30

A 62-year-old man with chronic hepatitis B develops hepatocellular carcinoma. Molecular studies reveal inactivation of p53. Which of the following best describes the normal role of p53 in preventing tumor development?

Accepted Answer

It induces apoptosis in cells with DNA damage. — p53 is a tumor suppressor protein that acts as a 'guardian of the genome.' In response to cellular stress, such as DNA damage, p53 can induce cell cycle arrest for repair or trigger apoptosis to eliminate damaged cells, thereby preventing the accumulation of mutations that could lead to cancer.

Question 31

A point mutation in the RAS gene that locks it in an active GTP-bound state results in which cellular effect?

Accepted Answer

Continuous activation of downstream signaling pathways promoting cell growth and survival — RAS proteins are molecular switches that, when active, bind GTP and signal downstream. A mutation that locks RAS in its GTP-bound state leads to constitutive activation of downstream signaling pathways (e.g., MAPK, PI3K/Akt), promoting uncontrolled cell proliferation, survival, and other cancer-related phenotypes.

Question 32

The ERBB2 (HER2/neu) oncogene contributes to tumorigenesis primarily by:

Accepted Answer

Activating signaling pathways that drive cell proliferation and survival — ERBB2 (HER2/neu) is a receptor tyrosine kinase. Its amplification and overexpression lead to constitutive activation of intracellular signaling cascades, such as the PI3K-Akt and MAPK pathways, which are critical for cell proliferation, survival, and growth.

Question 33

Autocrine stimulation of growth factor receptors is best exemplified by:

Accepted Answer

A tumor cell secreting a growth factor that binds to its own surface receptors. — Autocrine stimulation occurs when a cell produces a signaling molecule (like a growth factor) that acts on receptors located on its own surface, thereby stimulating its own growth and survival. This is a common mechanism in cancer.

Question 34

Mutation of the RB1 gene promotes cancer development by:

Accepted Answer

Releasing the E2F transcription factor, leading to uncontrolled cell cycle progression. — The RB1 gene encodes the retinoblastoma protein (Rb), which normally binds to and inhibits the E2F transcription factor. When Rb is mutated or inactivated, E2F is released, leading to the transcription of genes required for cell cycle progression (e.g., S-phase genes), driving uncontrolled cell proliferation.

Question 35

Loss of function of the TGF-β signaling pathway contributes to tumorigenesis by:

Accepted Answer

Stimulating cell proliferation and inhibiting differentiation. — Transforming growth factor-beta (TGF-β) normally acts as a tumor suppressor by inhibiting cell proliferation and promoting differentiation in many cell types. Loss of function of the TGF-β signaling pathway removes these inhibitory signals, allowing for uncontrolled proliferation and promoting an epithelial-to-mesenchymal transition (EMT).

Question 36

The anti-apoptotic effect of BCL-2 overexpression in follicular lymphoma occurs due to:

Accepted Answer

Inhibition of pro-apoptotic proteins like BAX and BAK. — BCL-2 is an anti-apoptotic protein. Overexpression of BCL-2, as seen in follicular lymphoma (often due to the t(14;18) translocation), prevents the activation of pro-apoptotic proteins (like BAX and BAK) and thus inhibits the intrinsic pathway of apoptosis, leading to increased cell survival.

Weekly Pathology Exam - October 9, 2026 (Section A: MCQs) MCQs

Questions, Answers & Explanations