Weekly Pathology Exam - October 2, 2026 (Section A: MCQs)...

Question 1

A 62-year-old woman with IPF has worsening dyspnea over 2 weeks without infection. HRCT now shows new bilateral ground-glass opacities superimposed on her existing fibrosis. Most likely complication?

Accepted Answer

Acute exacerbation of IPF — New ground-glass opacities in a patient with IPF, especially with worsening dyspnea and without evidence of infection, are highly suggestive of an acute exacerbation of IPF. This is a common and serious complication.

Question 2

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

Accepted Answer

Restrictive pattern with reduced diffusion capacity — Idiopathic Pulmonary Fibrosis (IPF) is characterized by interstitial lung disease, leading to lung stiffness and reduced lung volumes (restrictive pattern). The fibrotic process also impairs gas exchange, resulting in a reduced diffusion capacity for carbon monoxide (DLCO).

Question 3

Which immunohistochemical marker distinguishes malignant mesothelioma from metastatic adenocarcinoma to the pleura?

Accepted Answer

Calretinin — Calretinin is a marker that is typically positive in malignant mesothelioma and negative in most metastatic adenocarcinomas to the pleura. CK7 is often positive in both, CK20 and TTF-1 are more typically associated with adenocarcinomas, particularly those of the lung or gastrointestinal tract.

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. Most likely type of effusion?

Accepted Answer

Transudate — Using Light's criteria: Fluid protein/serum protein ratio (2.1/7.0 = 0.3) is <0.5. Fluid LDH/serum LDH ratio (88/300 ≈ 0.29) is <0.6. Fluid LDH is <2/3 the upper limit of normal serum LDH (assuming upper limit is ~200 U/L, 88 is < ~133). These findings are characteristic of a transudative effusion, commonly seen in heart failure.

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. Most likely type of effusion?

Accepted Answer

Exudate — Using Light's criteria: Fluid protein/serum protein ratio (5.2/6.8 ≈ 0.76) is 0.5. Fluid LDH (420 U/L) is 2/3 the upper limit of normal serum LDH (assuming upper limit is ~200 U/L, 420 is ~133). These findings are characteristic of an exudative effusion. Given the history of breast cancer and malignant cells on cytology, this is a malignant pleural 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. Most likely diagnosis?

Accepted Answer

Chylothorax — A milky white pleural effusion with elevated triglyceride levels (typically 110 mg/dL) is diagnostic of chylothorax, which results from leakage of lymphatic fluid from the thoracic duct. Thoracic duct injury is a common cause.

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. Most likely diagnosis?

Accepted Answer

Granulomatosis with polyangiitis (GPA) — This constellation of symptoms (sinusitis, epistaxis, haemoptysis, haematuria), bilateral cavitating lung nodules, red cell casts in urine, and a strongly positive c-ANCA (PR3-ANCA) is classic for Granulomatosis with Polyangiitis (formerly Wegener's granulomatosis).

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. Most likely diagnosis?

Accepted Answer

Granulomatosis with polyangiitis (GPA) — Eosinophilic granulomatosis with polyangiitis (EGPA), also known as Churg-Strauss syndrome, is characterized by asthma, peripheral eosinophilia, Löffler's syndrome (transient pulmonary infiltrates), and systemic vasculitis (often presenting as mononeuritis multiplex). p-ANCA positivity is also common.

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. Most likely diagnosis?

Accepted Answer

Goodpasture syndrome — The combination of hemoptysis, progressive dyspnea, renal involvement (proteinuria, red cell casts), anti-GBM antibodies, and linear IgG deposition on renal biopsy is diagnostic of Goodpasture syndrome, a type II hypersensitivity reaction targeting the glomerular and alveolar basement membranes.

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. Most likely diagnosis?

Accepted Answer

Silicosis — Occupational history of silica dust exposure, progressive dyspnea, upper lobe nodules, and eggshell calcification of hilar lymph nodes are pathognomonic for silicosis. A restrictive pattern on PFTs is also typical.

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. Most likely diagnosis?

Accepted Answer

Pulmonary arterial hypertension (PAH) — Progressive exertional dyspnea, syncope, loud P2, and elevated pulmonary artery pressure with a normal pulmonary capillary wedge pressure are characteristic findings of pulmonary arterial hypertension (PAH). The normal PCWP rules out significant left heart failure as the primary cause.

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. Most likely type of respiratory failure?

Accepted Answer

Type 2 respiratory failure (hypercapnic) — The ABG shows significant hypoxemia (PaO2 55 mmHg) and hypercapnia (PaCO2 72 mmHg), with a compensated metabolic alkalosis (HCO3 32 mEq/L, indicating chronic retention of CO2). This pattern, especially with drowsiness, signifies Type 2 (hypercapnic) respiratory failure, often superimposed on underlying hypoxemia in severe COPD.

Question 13

Which of the following lab tests is most sensitive for detecting early renal damage from diabetes mellitus?

Accepted Answer

Urinary albumin-to-creatinine ratio (UACR) — Microalbuminuria, detected by the urinary albumin-to-creatinine ratio (UACR), is the earliest clinical sign of diabetic nephropathy. Serum creatinine and BUN may not be elevated until significant renal function has been lost, and eGFR is also less sensitive than UACR in the early stages.

Question 14

A 52-year-old woman undergoes thyroidectomy for a well-circumscribed, encapsulated thyroid nodule. History 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 histologically resembling normal thyroid tissue is characteristic of a benign follicular adenoma. Malignant follicular lesions (carcinomas) typically lack a capsule or show capsular invasion.

Question 15

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 and hyperchromasia — While increased mitotic activity, necrosis, and glandular formation can be seen in both benign and malignant lesions, significant nuclear pleomorphism and hyperchromasia are hallmarks of malignancy and are key features for distinguishing a carcinoma from a benign polyp or adenoma.

Question 16

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

Accepted Answer

Constitutive tyrosine kinase activity — The Philadelphia chromosome (t(9;22)) in CML creates the BCR-ABL fusion gene, which encodes a constitutively active tyrosine kinase. This uncontrolled kinase activity drives the proliferation of myeloid cells.

Question 17

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

Increased cell proliferation and survival signaling — HER2/neu is a receptor tyrosine kinase. Amplification of its gene leads to overexpression of the HER2 protein, which then dimerizes and activates downstream signaling pathways (e.g., PI3K/Akt, MAPK) that promote uncontrolled cell proliferation, survival, and growth.

Question 18

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 — This scenario perfectly illustrates the 'two-hit hypothesis' (also known as Knudson's hypothesis) for tumor suppressor genes. Both inherited (germline) and acquired (somatic) mutations are required for tumor development. The RB gene is a classic example of a tumor suppressor gene.

Question 19

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

Inducing cell cycle arrest or apoptosis in response to DNA damage — p53 is a crucial tumor suppressor gene that acts as a 'guardian of the genome.' In response to cellular stress, such as DNA damage, p53 can halt the cell cycle to allow for repair or induce apoptosis if the damage is irreparable, thereby preventing the accumulation of mutations that can lead to cancer.

Question 20

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

Accepted Answer

Constitutive activation of downstream signaling pathways promoting proliferation — RAS proteins are molecular switches that cycle between an inactive GDP-bound state and an active GTP-bound state. A mutation that locks RAS in the active GTP-bound state leads to continuous signaling downstream, promoting uncontrolled cell proliferation and survival, a common mechanism in oncogenesis.

Question 21

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

Accepted Answer

Encoding a receptor tyrosine kinase that signals for cell growth and proliferation — The ERBB2 gene encodes for the HER2 receptor, a member of the epidermal growth factor receptor family. When overexpressed or amplified, it leads to constitutive activation of downstream signaling pathways that drive cell proliferation and survival, contributing to tumorigenesis.

Question 22

Autocrine stimulation of growth factor receptors is best exemplified by:

Accepted Answer

A tumor cell secreting a growth factor that binds to receptors on its own surface — Autocrine signaling occurs when a cell produces and secretes a molecule (in this case, a growth factor) that then binds to receptors on its own cell surface, stimulating its own growth and proliferation. This is a common mechanism in cancer.

Question 23

Mutation of the RB1 gene promotes cancer development by:

Accepted Answer

Removing the brake on the cell cycle, allowing uncontrolled proliferation — The RB1 gene encodes the retinoblastoma protein (Rb), which is a key regulator of the cell cycle. Rb normally binds to transcription factors (like E2F), inhibiting their activity and preventing the cell from progressing through the G1/S phase transition. Loss of functional Rb protein releases this inhibition, allowing uncontrolled cell division.

Question 24

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

Accepted Answer

Reducing its normal inhibitory effect on cell proliferation and promoting angiogenesis — Transforming Growth Factor-beta (TGF-β) typically acts as a tumor suppressor by inhibiting cell proliferation and promoting apoptosis in normal cells. In many cancers, mutations lead to loss of TGF-β signaling, removing this inhibitory effect and allowing cells to proliferate unchecked. In later stages, TGF-β can paradoxically promote invasion and metastasis.

Question 25

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

Accepted Answer

Direct inhibition of pro-apoptotic proteins like Bax and Bak — BCL-2 is an anti-apoptotic protein. Overexpression of BCL-2, often due to the t(14;18) translocation in follicular lymphoma, inhibits the function of pro-apoptotic proteins (like Bax and Bak), thereby preventing the intrinsic pathway of apoptosis and allowing malignant B cells to survive.

Question 26

The genetic defect associated with Fabry's disease is most likely carried on which chromosome?

Accepted Answer

X chromosome — Fabry disease is an X-linked lysosomal storage disorder caused by mutations in the GLA gene, which is located on the X chromosome. This explains its typically X-linked recessive inheritance pattern.

Question 27

What is the role of dietary iodine in thyroid hormone secretion?

Accepted Answer

Essential component for the synthesis of thyroid hormones (T3 and T4) — Iodine is a critical raw material required for the synthesis of thyroid hormones (thyroxine/T4 and triiodothyronine/T3) by the thyroid gland. Iodine atoms are incorporated into tyrosine residues within the thyroglobulin molecule.

Question 28

Movement of Cl- ion from gastric cells into the gastric cavity is a function of which transporter?

Accepted Answer

K+/Cl- cotransporter — The K+/Cl- cotransporter (also known as the chloride channel in this context) facilitates the movement of chloride ions from the gastric parietal cells into the gastric lumen, which is essential for the production of hydrochloric acid (HCl). The proton pump (H+/K+-ATPase) then pumps H+ into the lumen, and the K+ is recycled to maintain the electrochemical gradient for chloride movement.

Question 29

Myeloid cells in innate and adaptive immunity EXCLUDE the following:

Accepted Answer

Natural Killer (NK) cells — Natural Killer (NK) cells are lymphocytes, derived from the common lymphoid progenitor. Neutrophils, macrophages, and dendritic cells are all myeloid cells, originating from the common myeloid progenitor.

Question 30

The following statement is FALSE about the cells arising from the common lymphoid progenitor:

Accepted Answer

They are the primary cells responsible for phagocytosis. — Cells arising from the common lymphoid progenitor include B cells, T cells, and NK cells, which are primarily involved in the adaptive and innate (NK cells) immune responses. Phagocytosis is a primary function of myeloid cells like macrophages and neutrophils, not lymphoid cells.

Question 31

While complete aerobic oxidation of one mole of glucose in the cell yields approximately 38 moles of ATP, complete catabolism of one mole of a 6-carbon fatty acid through the citric acid cycle yields approximately:

Accepted Answer

60-70 moles of ATP — Fatty acid oxidation (beta-oxidation) yields significantly more ATP per carbon atom than glucose oxidation. For a 6-carbon fatty acid (like palmitate which has 16 carbons, but using a simplified example), the process of beta-oxidation and subsequent entry into the citric acid cycle and oxidative phosphorylation generates a much higher ATP yield than glucose. For a C6 fatty acid, it would be roughly around 40-50 ATP molecules after the initial activation step.

Question 32

Immune privileged sites include the following EXCEPT:

Accepted Answer

Skin — Immune privilege refers to sites in the body that are partially or wholly isolated from the immune system, allowing tolerance of foreign antigens. These include the brain, eyes, and testes, where an inflammatory response could cause severe damage. The skin, while having immune surveillance, is not considered an immune privileged site due to its exposure to the external environment and robust immune cell presence.

Question 33

The human genome:

Accepted Answer

Is identical in every somatic cell of an individual. — The human genome, with its approximately 3 billion base pairs, is largely identical in every somatic cell of an individual. While it contains genes for many proteins, not all proteins are encoded by it (e.g., mitochondrial proteins). A significant portion of the genome is non-coding (introns, regulatory regions, etc.).

Question 34

The following are characteristics of skeletal muscle fibres EXCEPT:

Accepted Answer

Involuntary control — Skeletal muscle fibers are characterized by being multinucleated, having a striated appearance due to the organized arrangement of actin and myosin filaments, and being contractile. However, their contraction is under voluntary control, mediated by somatic motor neurons.

Question 35

Increasing the frequency of stimulation so that a muscle contracts without relaxation is called:

Accepted Answer

Tetanus — Tetanus (or tetanic contraction) occurs when the frequency of muscle fiber stimulation is so high that individual muscle twitches merge together, resulting in a sustained, maximal contraction without any relaxation between stimuli.

Question 36

Which type of sensation is most affected if the lesion is in the sensory cortex?

Accepted Answer

Fine touch and proprioception — The primary somatosensory cortex (located in the postcentral gyrus) is responsible for processing fine touch, vibration, two-point discrimination, and proprioception. While it receives input related to pain and temperature, these sensations are also processed in other areas, and deficits in pain/temperature are more commonly associated with lesions in the spinothalamic tract or thalamus.

Question 37

There are several important differences between a chemical and an electrical synapse. Which of the following statements does NOT constitute a difference between these two types of synapses?

Accepted Answer

Electrical synapses are generally slower than chemical synapses. — Electrical synapses are typically faster than chemical synapses due to the direct flow of ions through gap junctions. Chemical synapses, involving neurotransmitter diffusion and receptor binding, introduce a synaptic delay, making them generally slower.

Weekly Pathology Exam - October 2, 2026 (Section A: MCQs)...

Questions, Answers & Explanations