NBME CBSE (USMLE STEP 1) 2026-2027: THE ULTIMATE
MIXED EXAM 100 High-Yield Clinical Vignettes with
Integrated Basic Science | Derived from NBME
Comprehensive Basic Science Examination Content
Outline | Guaranteed First-Time Pass
Q1.A 55-year-old male with a 40-pack-year smoking history presents with a
persistent cough, hemoptysis, and a 15-pound weight loss over 3 months. A
chest CT reveals a 4 cm mass in the right main bronchus with mediastinal
lymphadenopathy. Biopsy shows malignant cells with abundant cytoplasm
and central nuclei forming a "pagetoid" pattern. Laboratory studies show
serum sodium of 116 mEq/L, urine osmolality of 450 mOsm/kg, and serum
osmolality of 250 mOsm/kg. Which of the following mechanisms is MOST
responsible for the patient's electrolyte abnormality?
A) Ectopic ACTH production leading to cortisol excess
B) Ectopic ADH production leading to water retention
C) Tumor secretion of atrial natriuretic peptide
D) Direct invasion of the hypothalamus
E) Syndrome of inappropriate antidiuretic hormone due to chemotherapy
Correct Answer: B
Rationale: This patient has small cell lung carcinoma (SCLC) with syndrome
of inappropriate antidiuretic hormone (SIADH) . SCLC is the most common
,cause of SIADH among malignancies. The tumor produces **ectopic ADH
(vasopressin)** , leading to water retention, hyponatremia (Na 116 mEq/L),
concentrated urine (urine osmolality >100 mOsm/kg), and low serum
osmolality. Ectopic ACTH production (A) would cause Cushing syndrome
with hypokalemia, not hyponatremia. ANP secretion (C) would cause
natriuresis and hypovolemia. Hypothalamic invasion (D) is rare and would
cause central diabetes insipidus. Chemotherapy-induced SIADH (E) is
possible but less common than tumor-induced.
Q2. A 65-year-old female with a history of type 2 diabetes and
hypertension presents with a 3-month history of progressive fatigue,
weight loss, and abdominal pain. Physical examination reveals
hepatomegaly and ascites. Laboratory studies show elevated serum
alkaline phosphatase, alpha-fetoprotein (AFP) > 10,000 ng/mL, and positive
hepatitis B surface antigen. A liver biopsy reveals malignant cells forming
glandular structures. Which of the following genetic mutations is MOST
commonly associated with this condition in patients with hepatitis B?
A) TP53 mutation
B) CTNNB1 mutation
C) AXIN1 mutation
D) ARID1A mutation
E) TERT promer mutation
Correct Answer: A
,Rationale: This patient has hepatocellular carcinoma (HCC) in the setting of
chronic hepatitis B infection. In HBV-associated HCC, TP53 mutations are
the most common genetic alterations, occurring in 30-50% of cases. The
HBx protein of HBV binds to and inactivates p53, promoting carcinogenesis.
CTNN mutations (B) are more common in HCV-associated HCC and alcohol-
related HCC. AXIN1 (C), ARID1A (D), and TERT promoter (E) mutations are
also seen but are less common in HBV-associated HCC.
Q3.A 58-year-old male with a history of chronic pancreatitis presents with
jaundice, dark urine, and light-colored stools. Laboratory studies show
elevated serum bilirubin, alkaline phosphatase, and CA 19-9. A CT scan
reveals a 3 cm mass in the head of the pancreas. Which of the following is
the MOST likely mechanism of the patient's jaundice?
A) Intrahepatic cholestasis due to bile canalicular injury
B) Extrahepatic obstruction of the common bile duct
C) Hemolysis due to microangiopathic anemia
D) Hepatocellular injury due to metastatic disease
E) Gilbert syndrome with unconjugated hyperbilirubinemia
Correct Answer: B
Rationale: This patient has pancreatic adenocarcinoma in the head of the
pancreas. The mass compresses the common bile duct as it passes through
, the pancreatic head, causing extrahepatic obstruction. This leads to
conjugated hyperbilirubinemia (elevated direct bilirubin), dark urine
(bilirubinuria), light-colored stools (absence of urobilinogen), and pruritus
(bile salt deposition). Intrahepatic cholestasis (A) is less likely. Hemolysis (C)
causes unconjugated hyperbilirubinemia. Hepatocellular injury (D) would
elevate transaminases. Gilbert syndrome (E) is a benign condition with mild
unconjugated hyperbilirubinemia.
Q4. A 45-year-old female with a history of systemic lupus erythematosus
presents with a 2-week history of progressive weakness, dyspnea on
exertion, and a non-productive cough. Physical examination reveals
bilateral crackles at the lung bases. A chest X-ray shows bilateral interstitial
infiltrates with a "ground-glass" appearance. Laboratory studies show a
positive antinuclear antibody and anti-dsDNA antibodies. A lung biopsy
reveals diffuse alveolar damage with hyaline membranes. Which of the
following is the MOST likely diagnosis?
A) Lupus pneumonitis
B) Diffuse alveolar hemorrhage
C) Pulmonary embolism
D) Community-acquired pneumonia
E) Pulmonary fibrosis
Correct Answer: A
Ration
MIXED EXAM 100 High-Yield Clinical Vignettes with
Integrated Basic Science | Derived from NBME
Comprehensive Basic Science Examination Content
Outline | Guaranteed First-Time Pass
Q1.A 55-year-old male with a 40-pack-year smoking history presents with a
persistent cough, hemoptysis, and a 15-pound weight loss over 3 months. A
chest CT reveals a 4 cm mass in the right main bronchus with mediastinal
lymphadenopathy. Biopsy shows malignant cells with abundant cytoplasm
and central nuclei forming a "pagetoid" pattern. Laboratory studies show
serum sodium of 116 mEq/L, urine osmolality of 450 mOsm/kg, and serum
osmolality of 250 mOsm/kg. Which of the following mechanisms is MOST
responsible for the patient's electrolyte abnormality?
A) Ectopic ACTH production leading to cortisol excess
B) Ectopic ADH production leading to water retention
C) Tumor secretion of atrial natriuretic peptide
D) Direct invasion of the hypothalamus
E) Syndrome of inappropriate antidiuretic hormone due to chemotherapy
Correct Answer: B
Rationale: This patient has small cell lung carcinoma (SCLC) with syndrome
of inappropriate antidiuretic hormone (SIADH) . SCLC is the most common
,cause of SIADH among malignancies. The tumor produces **ectopic ADH
(vasopressin)** , leading to water retention, hyponatremia (Na 116 mEq/L),
concentrated urine (urine osmolality >100 mOsm/kg), and low serum
osmolality. Ectopic ACTH production (A) would cause Cushing syndrome
with hypokalemia, not hyponatremia. ANP secretion (C) would cause
natriuresis and hypovolemia. Hypothalamic invasion (D) is rare and would
cause central diabetes insipidus. Chemotherapy-induced SIADH (E) is
possible but less common than tumor-induced.
Q2. A 65-year-old female with a history of type 2 diabetes and
hypertension presents with a 3-month history of progressive fatigue,
weight loss, and abdominal pain. Physical examination reveals
hepatomegaly and ascites. Laboratory studies show elevated serum
alkaline phosphatase, alpha-fetoprotein (AFP) > 10,000 ng/mL, and positive
hepatitis B surface antigen. A liver biopsy reveals malignant cells forming
glandular structures. Which of the following genetic mutations is MOST
commonly associated with this condition in patients with hepatitis B?
A) TP53 mutation
B) CTNNB1 mutation
C) AXIN1 mutation
D) ARID1A mutation
E) TERT promer mutation
Correct Answer: A
,Rationale: This patient has hepatocellular carcinoma (HCC) in the setting of
chronic hepatitis B infection. In HBV-associated HCC, TP53 mutations are
the most common genetic alterations, occurring in 30-50% of cases. The
HBx protein of HBV binds to and inactivates p53, promoting carcinogenesis.
CTNN mutations (B) are more common in HCV-associated HCC and alcohol-
related HCC. AXIN1 (C), ARID1A (D), and TERT promoter (E) mutations are
also seen but are less common in HBV-associated HCC.
Q3.A 58-year-old male with a history of chronic pancreatitis presents with
jaundice, dark urine, and light-colored stools. Laboratory studies show
elevated serum bilirubin, alkaline phosphatase, and CA 19-9. A CT scan
reveals a 3 cm mass in the head of the pancreas. Which of the following is
the MOST likely mechanism of the patient's jaundice?
A) Intrahepatic cholestasis due to bile canalicular injury
B) Extrahepatic obstruction of the common bile duct
C) Hemolysis due to microangiopathic anemia
D) Hepatocellular injury due to metastatic disease
E) Gilbert syndrome with unconjugated hyperbilirubinemia
Correct Answer: B
Rationale: This patient has pancreatic adenocarcinoma in the head of the
pancreas. The mass compresses the common bile duct as it passes through
, the pancreatic head, causing extrahepatic obstruction. This leads to
conjugated hyperbilirubinemia (elevated direct bilirubin), dark urine
(bilirubinuria), light-colored stools (absence of urobilinogen), and pruritus
(bile salt deposition). Intrahepatic cholestasis (A) is less likely. Hemolysis (C)
causes unconjugated hyperbilirubinemia. Hepatocellular injury (D) would
elevate transaminases. Gilbert syndrome (E) is a benign condition with mild
unconjugated hyperbilirubinemia.
Q4. A 45-year-old female with a history of systemic lupus erythematosus
presents with a 2-week history of progressive weakness, dyspnea on
exertion, and a non-productive cough. Physical examination reveals
bilateral crackles at the lung bases. A chest X-ray shows bilateral interstitial
infiltrates with a "ground-glass" appearance. Laboratory studies show a
positive antinuclear antibody and anti-dsDNA antibodies. A lung biopsy
reveals diffuse alveolar damage with hyaline membranes. Which of the
following is the MOST likely diagnosis?
A) Lupus pneumonitis
B) Diffuse alveolar hemorrhage
C) Pulmonary embolism
D) Community-acquired pneumonia
E) Pulmonary fibrosis
Correct Answer: A
Ration
