Drug Classification · Questions 1–6
Identify the pharmacological class or categorical label for each drug or receptor. Vocabulary preparation is sufficient to answer every question in this section.
Question 1
Which of the following drugs is classified as an anti-HER2 monoclonal antibody?
Correct Answer
B) Trastuzumab
Rationale
Trastuzumab is a humanized IgG1 monoclonal antibody that binds the fourth extracellular domain of HER2 (human epidermal growth factor receptor 2). Bevacizumab is an anti-VEGF (vascular endothelial growth factor) monoclonal antibody. Rituximab is an anti-CD20 monoclonal antibody. Cetuximab is an anti-EGFR (epidermal growth factor receptor) monoclonal antibody.
Question 2
Which of the following drugs is classified as an anti-CD20 monoclonal antibody?
Correct Answer
D) Rituximab
Rationale
Rituximab is a chimeric IgG1 monoclonal antibody that binds CD20 (cluster of differentiation 20), a B-cell surface antigen. Daratumumab targets CD38. Trastuzumab targets HER2 (human epidermal growth factor receptor 2). Denosumab targets RANKL (receptor activator of NF-kB ligand).
Question 3
Which of the following drugs is classified as an anti-VEGF monoclonal antibody?
Correct Answer
A) Bevacizumab
Rationale
Bevacizumab is a humanized IgG1 monoclonal antibody that binds all isoforms of VEGF-A (vascular endothelial growth factor A), preventing its binding to VEGF receptors on endothelial cells and inhibiting tumor angiogenesis. Cetuximab is an anti-EGFR monoclonal antibody. Trastuzumab is an anti-HER2 monoclonal antibody. Rituximab is an anti-CD20 monoclonal antibody.
Question 4
Which of the following antibody-drug conjugates is classified as an anti-CD30 agent?
Correct Answer
C) Brentuximab vedotin
Rationale
Brentuximab vedotin is an antibody-drug conjugate linking an anti-CD30 (cluster of differentiation 30, a tumor necrosis factor receptor superfamily member) IgG1 antibody to the microtubule-disrupting payload MMAE (monomethyl auristatin E). Sacituzumab govitecan targets TROP-2. Trastuzumab emtansine targets HER2. Polatuzumab vedotin targets CD79b.
Question 5
Which of the following drugs is classified as an anti-RANKL monoclonal antibody?
Correct Answer
B) Denosumab
Rationale
Denosumab is a fully human IgG2 monoclonal antibody that binds RANKL (receptor activator of NF-kB ligand), preventing osteoclast differentiation and activation. Bevacizumab targets VEGF-A. Daratumumab targets CD38. Rituximab targets CD20.
Question 6
Which of the following antibody-drug conjugates is classified as an anti-TROP-2 agent?
Correct Answer
D) Sacituzumab govitecan
Rationale
Sacituzumab govitecan is an antibody-drug conjugate linking an anti-TROP-2 (trophoblast cell surface antigen 2) IgG1 antibody to SN-38, the active topoisomerase I inhibitor metabolite of irinotecan. Brentuximab vedotin targets CD30. Trastuzumab emtansine targets HER2 and carries a maytansinoid payload. Polatuzumab vedotin targets CD79b.
Core Pharmacology · Questions 7–14
Apply your understanding of drug mechanisms, pharmacokinetics, and adverse effects. Each question requires one reasoning step.
Question 7
A patient receiving trastuzumab for HER2-positive breast cancer develops an asymptomatic decline in left ventricular ejection fraction. Which of the following best explains why trastuzumab cardiotoxicity differs in mechanism from anthracycline cardiotoxicity?
Correct Answer
A) Trastuzumab inhibits HER2 and HER4 signaling in cardiomyocytes, impairing a cardiac repair and stress-response pathway; this cardiotoxicity is generally reversible upon drug discontinuation, in contrast to anthracycline cardiotoxicity, which results from irreversible free radical-mediated damage to cardiomyocyte mitochondria
Rationale
Anthracycline cardiotoxicity results from irreversible free radical-mediated damage to cardiomyocyte mitochondria, is dose-dependent and cumulative, and is largely irreversible. Trastuzumab cardiotoxicity has an entirely different mechanism: HER2 (ErbB2) and HER4 signaling in cardiomyocytes is required for cardiac stress-response hypertrophy and protection against anthracycline-induced damage. Trastuzumab inhibits this cardioprotective pathway, producing cardiomyopathy that is generally not dose-dependent and is largely reversible after drug discontinuation — LVEF (left ventricular ejection fraction) typically recovers when trastuzumab is held. This mechanistic distinction is clinically important because it governs the approach to managing reduced ejection fraction: trastuzumab can often be restarted after recovery, whereas anthracycline-associated cardiomyopathy is managed as permanent damage.
Question 8
A patient with HER2-positive breast cancer is receiving an anthracycline-based chemotherapy regimen. Her oncologist plans to add trastuzumab to the current cycle to complete the regimen simultaneously. Which of the following best explains why concurrent administration of trastuzumab with anthracyclines is contraindicated?
Correct Answer
C) HER2 signaling in cardiomyocytes normally provides a protective stress-response that limits anthracycline-induced myocardial damage; blocking this pathway with trastuzumab during anthracycline therapy removes that protection and produces synergistic, severe cardiomyopathy
Rationale
HER2 (ErbB2) signaling in cardiomyocytes is a required component of the cardiac stress-response pathway that normally limits and repairs anthracycline-induced myocardial damage. When trastuzumab blocks this pathway during active anthracycline therapy, the cardiomyocytes lose their protective response precisely when it is most needed — during exposure to a directly cardiotoxic agent. The result is synergistically severe cardiomyopathy with unacceptably high rates of clinically significant heart failure. The standard practice is to complete anthracycline-based chemotherapy first, then initiate trastuzumab after the last anthracycline dose. Trastuzumab is a monoclonal antibody with no cytochrome P450 metabolism and does not affect anthracycline pharmacokinetics. Anthracyclines do not bind the HER2 receptor. The mechanism is pharmacodynamic cardiomyocyte vulnerability, not hypersensitivity or mast cell activation.
Question 9
A patient receiving bevacizumab for metastatic colorectal cancer develops new-onset hypertension requiring antihypertensive therapy. Which of the following best explains the mechanism of this adverse effect?
Correct Answer
B) Inhibition of VEGF-A signaling in vascular endothelium reduces the production of nitric oxide and prostacyclin, both of which normally maintain vasodilation; their loss results in vasoconstriction and hypertension
Rationale
VEGF-A (vascular endothelial growth factor A) signaling in vascular endothelium drives the production of nitric oxide via endothelial nitric oxide synthase and prostacyclin via cyclooxygenase, both of which are potent vasodilators that maintain normal vascular tone. Bevacizumab binds and neutralizes VEGF-A, withdrawing this vasodilatory signaling. Without nitric oxide and prostacyclin production, vascular smooth muscle constricts, raising systemic vascular resistance and blood pressure. This mechanism — endothelial vasodilator deprivation — explains why hypertension is a class effect of all anti-VEGF agents and why it typically appears within the first cycle of therapy. Activation of the renin-angiotensin-aldosterone system through juxtaglomerular cells, direct angiotensin II receptor binding, and beta-1 adrenergic stimulation are not the mechanisms of bevacizumab-induced hypertension.
Question 10
A patient receiving cetuximab for metastatic colorectal cancer is found to have a serum magnesium of 0.6 mg/dL (reference: 1.7 to 2.2 mg/dL) after six weeks of therapy. Which of the following best explains the mechanism of this adverse effect?
Correct Answer
D) Cetuximab blocks EGFR in the distal convoluted tubule, reducing expression of the TRPM6 magnesium channel that is required for active renal magnesium reabsorption, causing renal magnesium wasting
Rationale
EGFR (epidermal growth factor receptor) is expressed in the distal convoluted tubule of the nephron, where it regulates the expression of TRPM6 (transient receptor potential melastatin 6), the magnesium channel responsible for active magnesium reabsorption. Cetuximab blocks EGFR signaling in the distal convoluted tubule, reducing TRPM6 expression and impairing active magnesium reabsorption. The result is renal magnesium wasting — magnesium is lost in the urine despite low serum levels — producing hypomagnesemia that can be severe and symptomatic. This mechanism is shared by all anti-EGFR antibodies and is not observed with EGFR small molecule tyrosine kinase inhibitors, which block intracellular signaling differently. Intestinal absorption, direct magnesium chelation, and proximal tubule binding are not the mechanisms of cetuximab-induced hypomagnesemia.
Question 11
A patient with multiple comorbidities is starting trastuzumab for HER2-positive gastric cancer. Her pharmacist is reviewing potential drug interactions. Which of the following best describes why cytochrome P450-based drug interactions are not a clinical concern with trastuzumab?
Correct Answer
A) As a large IgG1 monoclonal antibody, trastuzumab is not metabolized by hepatic cytochrome P450 enzymes; it is catabolized throughout the body by proteolytic degradation to amino acids, which eliminates cytochrome P450-mediated drug interaction risk
Rationale
Therapeutic monoclonal antibodies including trastuzumab are large proteins (approximately 150 kDa) that are not substrates for hepatic cytochrome P450 enzymes. They are catabolized throughout the body — in endosomes, lysosomes, and tissue — by ubiquitous proteolytic enzymes to amino acids, which are reutilized in protein synthesis. This proteolytic catabolism is independent of the cytochrome P450 system, so drugs that inhibit or induce cytochrome P450 enzymes have no meaningful effect on trastuzumab clearance or exposure. This represents a fundamental pharmacokinetic distinction from the small molecule targeted agents in preceding modules. Trastuzumab is not a P-glycoprotein substrate in any clinically meaningful sense, is not glucuronidated by UGT1A1, and is not renally excreted — intact IgG molecules are too large for glomerular filtration.
Question 12
A patient receiving trastuzumab emtansine (T-DM1) for HER2-positive breast cancer develops grade 3 thrombocytopenia after two cycles. Which of the following best explains the mechanism of this adverse effect?
Correct Answer
C) The DM1 (emtansine) payload disrupts microtubule dynamics in megakaryocytes during the proplatelet formation process required for platelet release, reducing platelet production
Rationale
The thrombocytopenia associated with T-DM1 results from the DM1 (emtansine) cytotoxic payload, a potent microtubule polymerization inhibitor of the maytansinoid class. Megakaryocytes, the platelet precursors in the bone marrow, rely on an extensive microtubule network during proplatelet formation — the process by which megakaryocytes extend long cytoplasmic protrusions that fragment into individual platelets. DM1 disrupts this microtubule-dependent proplatelet formation, reducing platelet output from the bone marrow. This is a payload-mediated, on-target-tissue toxicity of the maytansinoid class. T-DM1 does not produce thrombocytopenia through antibody-dependent cellular cytotoxicity against HER2-expressing natural killer cells, through immune-mediated platelet destruction, or through thrombopoietin receptor pathway inhibition.
Question 13
Trastuzumab deruxtecan (T-DXd) produces responses in HER2-low breast cancer, defined as tumors with very low HER2 expression that were previously classified as HER2-negative. Which of the following best explains the pharmacologic mechanism that enables T-DXd to be effective at these low levels of HER2 expression?
Correct Answer
B) T-DXd carries a cleavable linker that releases a membrane-permeable topoisomerase I inhibitor payload inside tumor cells; this payload diffuses across cell membranes into neighboring cells that may not express HER2, killing them through bystander activity that compensates for heterogeneous or low HER2 expression
Rationale
T-DXd carries a tetrapeptide-based cleavable linker that is cleaved by lysosomal cathepsins after internalization of the conjugate into HER2-expressing tumor cells. The released payload — a topoisomerase I inhibitor derived from the camptothecin class — is membrane-permeable, meaning it can diffuse across the cell membrane into neighboring cells in the tumor microenvironment, including cells that express little or no HER2. This bystander killing is potent enough to produce meaningful tumor responses even when HER2 expression is low and heterogeneous across the tumor mass. The high drug-to-antibody ratio of approximately 8 amplifies the amount of membrane-permeable payload released per internalization event, further enhancing bystander effect. T-DXd does not achieve HER2-low efficacy through higher HER2 binding affinity, through non-selective cellular uptake, or through diffusion of the intact conjugate across membranes.
Question 14
A patient with triple-negative breast cancer begins sacituzumab govitecan. Pharmacogenomic testing reveals she is homozygous for the UGT1A1*28 allele. Which of the following best explains the clinical significance of this finding?
Correct Answer
D) The UGT1A1*28 allele is a promoter variant that reduces UGT1A1 enzyme expression, impairing glucuronidation and elimination of the SN-38 payload; accumulation of SN-38 substantially increases the risk of severe neutropenia and diarrhea
Rationale
UGT1A1 (UDP-glucuronosyltransferase 1A1) is the primary enzyme responsible for glucuronidating SN-38, the active topoisomerase I inhibitor payload released from sacituzumab govitecan after linker cleavage. Glucuronidation converts SN-38 to the inactive SN-38 glucuronide, which is then excreted. The UGT1A1*28 allele is a promoter variant containing an extra TA repeat that reduces UGT1A1 transcription, resulting in lower UGT1A1 enzyme activity. In patients homozygous for UGT1A1*28 (the *28/*28 genotype, occurring in approximately 10 percent of patients), SN-38 is glucuronidated more slowly and accumulates to higher plasma concentrations, substantially increasing the risk of severe neutropenia and diarrhea. This is the same pharmacogenomic mechanism that governs irinotecan toxicity, because SN-38 is the active metabolite of irinotecan as well. The UGT1A1*28 allele reduces, not increases, UGT1A1 expression. It does not alter SN-38 binding to topoisomerase I, and it does not redirect metabolism to cytochrome P450 3A4.
Clinical Correlations · Questions 15–18
Apply pharmacological knowledge to clinical scenarios. Each vignette presents a patient situation; the question tests mechanism of action or drug selection.
Question 15
A 61-year-old man with relapsed multiple myeloma is about to receive his first infusion of daratumumab. Before the drug is ordered, his oncologist contacts the hospital blood bank. Which of the following best explains why this notification is required prior to initiating daratumumab therapy?
Correct Answer
C) Daratumumab binds CD38 expressed on the surface of red blood cells, causing pan-reactive false-positive indirect antiglobulin tests that can mask clinically significant alloantibodies and compromise safe blood transfusion compatibility testing
Rationale
Daratumumab binds CD38, a transmembrane glycoprotein expressed at high levels on myeloma cells but also present at lower levels on normal hematopoietic cells including red blood cells. When daratumumab coats circulating red blood cells, it causes pan-reactive false-positive indirect antiglobulin tests (indirect Coombs tests) — the drug on the red cell surface reacts with anti-human immunoglobulin reagents and masks any underlying alloantibodies against donor blood antigens. This creates a patient safety risk: if an alloantibody is present and goes undetected, a crossmatch-incompatible transfusion could be administered. The blood bank must be notified before the first dose so that all future compatibility testing uses special techniques — dithiothreitol treatment of reagent red blood cells or genotyping-based crossmatching — that can work around the daratumumab interference. This effect persists for months after the last dose.
Question 16
A 55-year-old woman with metastatic colorectal cancer has been receiving bevacizumab plus FOLFOX chemotherapy with good response. She develops symptomatic cholelithiasis and her surgeon plans elective laparoscopic cholecystectomy. Her last bevacizumab infusion was administered three weeks ago. Which of the following is the most appropriate next step based on bevacizumab's mechanism of action?
Correct Answer
A) Delay surgery for at least five additional weeks so that at least 28 days have elapsed since the last bevacizumab dose, then proceed with surgery after confirming no active wound healing complications
Rationale
Bevacizumab inhibits VEGF-A (vascular endothelial growth factor A), which is required not only for tumor angiogenesis but also for the neovascularization that underlies normal wound healing. Without adequate VEGF-A activity, new blood vessel formation in healing surgical wounds is impaired, substantially increasing the risk of wound dehiscence, infection, and anastomotic leak. The required hold period before elective surgery is at least 28 days after the last bevacizumab dose — not determined by when plasma concentrations become negligible, but by the time required to restore adequate wound-healing capacity. Three weeks after the last dose does not meet the 28-day minimum; surgery should be delayed a further five weeks to reach and exceed this threshold. Bevacizumab must also not be resumed until wound healing is confirmed — typically at least 28 days postoperatively. The 48-hour hold is inadequate given the drug's approximately 20-day half-life and the biologic nature of the wound healing impairment.
Question 17
A 44-year-old woman with HER2-positive early-stage breast cancer has completed four cycles of doxorubicin-cyclophosphamide chemotherapy. Her oncologist plans to continue with paclitaxel and trastuzumab. Which of the following best describes the appropriate timing for initiating trastuzumab based on its interaction with prior anthracycline therapy?
Correct Answer
B) Trastuzumab should be initiated after the last anthracycline dose has been given, because HER2 signaling in cardiomyocytes provides a cardioprotective stress response that limits anthracycline-induced myocardial damage; blocking this pathway during active anthracycline therapy produces synergistic cardiomyopathy
Rationale
HER2 (ErbB2) signaling in cardiomyocytes is required for the cardiac stress-response pathway that limits and repairs anthracycline-induced myocardial injury. If trastuzumab is given concurrently with an anthracycline such as doxorubicin, it eliminates this cardioprotective signaling precisely when the cardiomyocytes are under greatest anthracycline stress, producing synergistically severe cardiomyopathy at rates that are clinically unacceptable. The standard practice — confirmed in multiple pivotal trials — is to complete anthracycline-based chemotherapy first, then initiate trastuzumab after the last anthracycline dose, not concurrently. In this patient, doxorubicin-cyclophosphamide is now complete, and paclitaxel plus trastuzumab can be initiated together for the taxane portion of therapy. A six-month delay is not required — the rule is sequential administration, not an extended washout. Trastuzumab is not contraindicated after anthracyclines; the sequential regimen is the standard of care in HER2-positive early breast cancer.
Question 18
A 58-year-old man with diffuse large B-cell lymphoma is scheduled to begin rituximab-based chemotherapy. Pre-treatment serologic screening shows hepatitis B surface antigen (HBsAg) negative and hepatitis B core antibody (HBcAb) positive, indicating prior resolved hepatitis B infection. He has no detectable hepatitis B surface antibody (HBsAb). Which of the following is the most appropriate management based on the mechanism of rituximab-related hepatitis B risk?
Correct Answer
D) Initiate prophylactic antiviral therapy with entecavir or tenofovir before the first rituximab dose and continue it throughout rituximab therapy and for at least twelve months after completion, because rituximab-induced B-cell depletion removes immune control of occult hepatitis B, enabling potentially fatal viral reactivation
Rationale
Rituximab depletes B cells through CD20-directed antibody-dependent cellular cytotoxicity, complement-dependent cytotoxicity, and direct apoptosis induction. B cells are a key component of the immune memory that controls occult hepatitis B virus — virus that persists in hepatocytes in the form of covalently closed circular deoxyribonucleic acid (cccDNA) even after apparent clinical recovery. Patients who are HBcAb-positive without detectable HBsAg harbor occult hepatitis B that is held in check by immune surveillance. Rituximab-induced B-cell depletion removes this immune control, allowing viral replication to surge — hepatitis B reactivation can produce acute liver failure and death. Prophylactic antiviral therapy with entecavir or tenofovir, initiated before the first rituximab dose and continued throughout therapy and for at least 12 months after the last dose (the period required for B-cell reconstitution), is mandatory. Waiting for detectable viral load before treating is reactive management that risks fulminant reactivation during the monitoring interval. Vaccination is ineffective in the immunocompromised state and does not prevent reactivation of pre-existing occult infection. HBcAb positivity without HBsAb is not protective — it indicates resolved infection with persistent occult viral reservoir.