Chapter 34 — Anti-Cancer Drugs Part 2 — Module 3 — Monoclonal Antibodies and Antibody-Drug Conjugates
1. A 58-year-old woman with HER2-positive (human epidermal growth factor receptor 2-positive) metastatic breast cancer and mild hepatic impairment is starting trastuzumab, a therapeutic monoclonal antibody (mAb, a laboratory-produced antibody that binds a single specific target). The oncology pharmacist is asked whether the dose must be reduced for her liver disease. Which statement best explains the expected effect of hepatic impairment on the pharmacokinetics of a full-length immunoglobulin G (IgG) monoclonal antibody?
A) Hepatic impairment has minimal effect because monoclonal antibodies are catabolized by widespread proteolytic degradation to amino acids rather than metabolized by hepatic cytochrome P450 (CYP, the liver enzyme family that metabolizes most small-molecule drugs) enzymes
B) Hepatic impairment markedly increases antibody exposure because the liver is the primary site of IgG clearance through CYP3A4 metabolism
C) Hepatic impairment requires a dose increase because reduced hepatic protein synthesis accelerates antibody elimination
D) Hepatic impairment reduces antibody efficacy because bile excretion is the dominant elimination route for intact IgG
E) Hepatic impairment necessitates therapeutic drug monitoring because antibodies undergo extensive first-pass hepatic extraction
ANSWER: A
Rationale:
Therapeutic monoclonal antibodies are large proteins (approximately 150 kDa for a full IgG) that are eliminated by ubiquitous proteolytic catabolism to amino acids, which are then reused in protein synthesis. Because they are not substrates of hepatic CYP enzymes, hepatic impairment has minimal pharmacokinetic impact and dose adjustment for liver disease is generally not required.
Option B: Option B is incorrect because the liver is not the primary site of IgG clearance and antibodies are not CYP3A4 substrates; CYP-based metabolism applies to small-molecule drugs, not full-length antibodies.
Option C: Option C is incorrect because it inverts the relationship: reduced hepatic protein synthesis does not accelerate antibody elimination, and no dose increase is indicated.
Option D: Option D is incorrect because biliary excretion of intact IgG is not a meaningful elimination route; antibodies are catabolized to amino acids throughout the body.
Option E: Option E is incorrect because antibodies are administered intravenously or subcutaneously and do not undergo first-pass hepatic extraction, which is a phenomenon of orally absorbed small molecules.
2. A pharmacology instructor asks why therapeutic immunoglobulin G (IgG) monoclonal antibodies typically have half-lives of approximately 14 to 21 days, far longer than most small-molecule drugs. Which mechanism best explains the characteristically long half-life of IgG antibodies?
A) IgG antibodies are sequestered in adipose tissue and slowly released, prolonging their apparent half-life
B) The neonatal Fc receptor (FcRn) binds IgG in acidic endosomes (pH 6.0) after the antibody is taken up by cells, protecting it from lysosomal degradation and recycling it back into the circulation at physiological pH
C) IgG antibodies inhibit their own hepatic cytochrome P450 (CYP, the liver enzyme family metabolizing most small-molecule drugs) metabolism, slowing their clearance
D) IgG antibodies bind irreversibly to their tumor targets, preventing systemic elimination
E) IgG antibodies are continuously resynthesized by plasma cells, maintaining stable serum concentrations
ANSWER: B
Rationale:
The long half-life of therapeutic IgG is governed by the neonatal Fc receptor (FcRn). After pinocytosis into cells, IgG binds FcRn in the acidic environment of the endosome (pH 6.0), which protects it from being routed to lysosomes for degradation; the antibody is then released back into the circulation when exposed to physiological pH (7.4). This salvage-and-recycle pathway accounts for half-lives of roughly 14 to 21 days.
Option A: Option A is incorrect because IgG distributes primarily into plasma and interstitial fluid (volume of distribution approximately 3 to 8 liters) with limited tissue partitioning; adipose sequestration is not the mechanism.
Option C: Option C is incorrect because antibodies are not CYP substrates and do not affect CYP-mediated metabolism.
Option D: Option D is incorrect because target binding actually promotes elimination through target-mediated drug disposition, not prolonged survival of the antibody.
Option E: Option E is incorrect because therapeutic monoclonal antibodies are exogenously administered, not synthesized by the patient's plasma cells; endogenous resynthesis does not explain the half-life of an infused drug.
3. A monoclonal antibody shows substantially faster clearance and a shorter effective half-life at low doses, with clearance slowing and half-life lengthening as the dose increases. A loading dose is recommended to rapidly achieve therapeutic concentrations. Which pharmacokinetic phenomenon best explains this dose-dependent (nonlinear) behavior?
A) Saturable hepatic cytochrome P450 (CYP) metabolism that becomes overwhelmed at high antibody doses
B) Enterohepatic recirculation that returns antibody to the systemic circulation at high doses
C) Target-mediated drug disposition (TMDD), in which binding to the high-affinity target is itself a significant elimination route that is readily saturated at low concentrations but contributes little once the target is saturated at higher doses
D) Renal tubular reabsorption of intact antibody that increases at higher serum concentrations
E) Plasma protein binding displacement that frees more active antibody as the dose rises
ANSWER: C
Rationale:
Target-mediated drug disposition (TMDD) occurs when binding of an antibody to its high-affinity pharmacologic target constitutes a meaningful elimination pathway. At low, sub-saturating concentrations, the antibody is rapidly cleared by receptor-mediated endocytosis of the antibody-target complex, producing fast clearance and a short effective half-life. As the dose rises and the target becomes saturated, this route contributes proportionally less, clearance falls, and half-life lengthens (nonlinear pharmacokinetics). This is why loading doses are used to quickly reach target-saturating concentrations.
Option A: Option A is incorrect because antibodies are not CYP substrates; CYP saturation does not govern their clearance.
Option B: Option B is incorrect because intact IgG does not undergo enterohepatic recirculation.
Option D: Option D is incorrect because intact antibody is too large for meaningful glomerular filtration or tubular handling; renal reabsorption of IgG is not a clearance determinant.
Option E: Option E is incorrect because protein-binding displacement is a small-molecule concept and does not explain saturable target-mediated clearance of an antibody.
4. A resident is learning to read monoclonal antibody International Nonproprietary Names (INN, the standardized generic naming system). She notes that the suffix encodes the species source of the antibody, which correlates with immunogenicity (the tendency to provoke anti-drug antibodies). For the agent trastuzumab, what does the "-zu-" stem indicate about the antibody's source?
A) Fully murine (mouse-derived) antibody with the highest immunogenicity
B) Fully human antibody with the lowest immunogenicity
C) Chimeric antibody that is approximately 25 to 35 percent human sequence
D) Humanized antibody that is approximately 90 to 95 percent human sequence, with relatively low immunogenicity
E) A bispecific antibody engineered to bind two distinct antigens simultaneously
ANSWER: D
Rationale:
In the traditional INN nomenclature, the source substem encodes how much of the antibody is human in origin: "-o-" denotes murine (-omab), "-xi-" denotes chimeric (-ximab, roughly 25 to 35 percent human), "-zu-" denotes humanized (-zumab, roughly 90 to 95 percent human), and "-u-" denotes fully human (-umab, 100 percent human). Trastuzumab carries "-zu-," identifying it as a humanized antibody with relatively low immunogenicity.
Option A: Option A is incorrect because a fully murine antibody carries the "-omab" suffix and has the highest immunogenicity, not "-zumab."
Option B: Option B is incorrect because a fully human antibody carries "-umab" (e.g., panitumumab); "-zumab" is humanized, not fully human.
Option C: Option C is incorrect because chimeric antibodies carry "-ximab" (e.g., rituximab) and are only about 25 to 35 percent human.
Option E: Option E is incorrect because bispecific antibodies are designated by a "-bi-" stem and the suffix here encodes source, not bispecificity.
5. A patient develops a decline in left ventricular ejection fraction (LVEF, the percentage of blood pumped out of the left ventricle per beat) while receiving trastuzumab. The cardiologist contrasts this with anthracycline (e.g., doxorubicin) cardiotoxicity. Which statement best characterizes trastuzumab-associated cardiotoxicity?
A) It results from irreversible free-radical damage to cardiomyocyte mitochondria and DNA and is cumulative with dose
B) It is permanent and mandates immediate lifelong discontinuation in nearly all cases
C) It is caused by direct coronary vasospasm and presents as acute myocardial infarction
D) It is unrelated to HER2 (human epidermal growth factor receptor 2) signaling and reflects a nonspecific infusion effect
E) It results from inhibition of HER2/HER4-mediated cardiac stress-response signaling, is generally not dose-dependent, and is largely reversible after the drug is held
ANSWER: E
Rationale:
Trastuzumab cardiotoxicity arises from blockade of HER2/HER4 (ErbB) signaling in cardiomyocytes, which normally supports a protective stress-response and cardiac repair. Because the injury is functional rather than a fixed structural lesion, it is generally not dose-dependent and is largely reversible: the drug is held (typically 4 to 8 weeks), LVEF is reassessed, and therapy is usually reinitiated after recovery.
Option A: Option A is incorrect because it describes anthracycline cardiotoxicity, which is free-radical-mediated, cumulative, dose-dependent, and largely irreversible.
Option B: Option B is incorrect because trastuzumab cardiotoxicity is usually reversible and does not require permanent discontinuation in most cases; permanent discontinuation is reserved for persistent decline after hold-and-reassess cycles.
Option C: Option C is incorrect because the mechanism is impaired repair signaling, not coronary vasospasm or acute infarction.
Option D: Option D is incorrect because the toxicity is mechanistically tied to HER2/HER4 signaling in the heart, not a nonspecific infusion phenomenon.
6. A treatment plan for HER2-positive (human epidermal growth factor receptor 2-positive) early breast cancer includes an anthracycline-based regimen (doxorubicin-cyclophosphamide) and trastuzumab. Regarding the timing of these agents, which approach is correct?
A) Complete the anthracycline-based chemotherapy first, then begin trastuzumab after the last anthracycline dose, because concurrent administration produces unacceptably high rates of symptomatic heart failure
B) Administer trastuzumab and the anthracycline together in the same cycle to maximize synergistic tumor kill
C) Give trastuzumab first and then add the anthracycline only after HER2 receptors are fully saturated
D) Alternate the two drugs on the same day to balance their cardiac effects
E) Avoid anthracyclines entirely because trastuzumab is absolutely contraindicated with any prior anthracycline exposure
ANSWER: A
Rationale:
Concurrent administration of trastuzumab with an anthracycline is contraindicated because the combination caused unacceptably high rates of symptomatic heart failure (approximately 27 percent in the pivotal HER2 trial). The standard approach is sequential: complete the anthracycline-based chemotherapy first, then initiate trastuzumab after the final anthracycline dose, which reduces symptomatic cardiac events to roughly 2 to 4 percent.
Option B: Option B is incorrect because simultaneous administration is precisely what produces the prohibitive cardiotoxicity.
Option C: Option C is incorrect because there is no rationale for giving trastuzumab first to "saturate" receptors before an anthracycline; the concern is overlapping cardiac injury, not receptor occupancy.
Option D: Option D is incorrect because alternating the drugs on the same day still constitutes concurrent exposure and does not mitigate the additive cardiotoxicity.
Option E: Option E is incorrect because prior anthracycline exposure is not an absolute contraindication to trastuzumab; sequential use after completing anthracycline therapy is standard practice.
7. A patient on trastuzumab has a baseline left ventricular ejection fraction (LVEF, the percentage of blood ejected from the left ventricle per beat) of 62 percent. On routine surveillance, her LVEF is now measured. Which finding should prompt holding trastuzumab?
A) An LVEF of 58 percent with no symptoms
B) An LVEF that falls below 50 percent, or a decrease of 16 percentage points or more from baseline
C) An LVEF decrease of 5 percentage points from baseline
D) Any LVEF below 60 percent regardless of the magnitude of change
E) An LVEF reduction is never a reason to hold trastuzumab because its cardiotoxicity is benign
ANSWER: B
Rationale:
Trastuzumab is held when the LVEF falls below 50 percent or drops by 16 percentage points or more from baseline; it is permanently discontinued for persistent decline after two hold-and-reassess cycles. Baseline LVEF assessment is mandatory, with reassessment approximately every 3 months during therapy.
Option A: Option A is incorrect because an LVEF of 58 percent (a drop of only 4 points from a 62 percent baseline, still above 50 percent) does not meet the hold threshold.
Option C: Option C is incorrect because a 5-percentage-point decrease is below the 16-point threshold and does not by itself require holding the drug.
Option D: Option D is incorrect because the threshold is anchored at an absolute LVEF below 50 percent or a 16-point drop, not any value below 60 percent.
Option E: Option E is incorrect because trastuzumab cardiotoxicity is clinically significant and defined LVEF thresholds explicitly trigger holding the drug; it is not benign.
8. Pertuzumab is combined with trastuzumab and docetaxel for HER2-positive (human epidermal growth factor receptor 2-positive) breast cancer. Both antibodies target HER2 but bind different epitopes (distinct sites on the receptor). What is the principal mechanism by which pertuzumab complements trastuzumab?
A) Pertuzumab binds domain IV of HER2, the identical epitope bound by trastuzumab, simply increasing the total dose of antibody
B) Pertuzumab inhibits intracellular tyrosine kinase activity by entering the cytoplasm
C) Pertuzumab binds domain II of the HER2 extracellular domain and blocks HER2 dimerization with other ErbB-family receptors, particularly the HER2-HER3 heterodimer that drives potent oncogenic signaling
E) Pertuzumab cross-links HER2 receptors to form aggregates that are cleared by the kidney
ANSWER: C
Rationale:
Pertuzumab binds domain II of the HER2 extracellular domain, a different epitope from trastuzumab (which binds domain IV), and blocks HER2 from dimerizing with other ErbB-family members, especially the HER2-HER3 heterodimer that drives the most potent downstream signaling. Combining the two antibodies provides dual HER2 blockade at distinct epitopes, improving outcomes over trastuzumab alone.
Option A: Option A is incorrect because pertuzumab binds domain II, not the same domain IV epitope as trastuzumab; the benefit is complementary blockade, not merely added dose.
Option B: Option B is incorrect because pertuzumab is a monoclonal antibody acting on the extracellular receptor domain, not an intracellular tyrosine kinase inhibitor.
Option D: Option D is incorrect because depleting VEGF describes bevacizumab's anti-angiogenic mechanism, not pertuzumab.
Option E: Option E is incorrect because pertuzumab works by inhibiting dimerization-driven signaling, and intact IgG aggregates are not eliminated by renal clearance given their large molecular size.
9. A patient receiving bevacizumab, a monoclonal antibody against vascular endothelial growth factor A (VEGF-A), develops new hypertension. Which mechanism best explains bevacizumab-associated hypertension?
A) Direct agonism of vascular angiotensin II receptors causing vasoconstriction
B) Sodium and water retention from mineralocorticoid receptor activation
C) Increased sympathetic outflow from central nervous system stimulation
D) Withdrawal of VEGF-A signaling in the endothelium, which reduces nitric oxide and prostacyclin production and leads to vasoconstriction
E) Stimulation of erythropoietin production causing polycythemia and increased blood viscosity
ANSWER: D
Rationale:
Bevacizumab binds and neutralizes VEGF-A, including the isoforms that maintain normal endothelial function. Loss of VEGF-A signaling in the endothelium reduces synthesis of the vasodilators nitric oxide and prostacyclin, producing vasoconstriction and hypertension (seen in roughly 23 to 35 percent of patients). It is managed with standard antihypertensives such as dihydropyridine calcium channel blockers, angiotensin-converting enzyme (ACE) inhibitors, or angiotensin receptor blockers.
Option A: Option A is incorrect because bevacizumab does not act as an angiotensin II receptor agonist.
Option B: Option B is incorrect because the hypertension is endothelial and vasoconstrictive in origin, not driven by mineralocorticoid-mediated volume retention.
Option C: Option C is incorrect because the mechanism is loss of endothelial vasodilators, not central sympathetic activation.
Option E: Option E is incorrect because bevacizumab does not raise erythropoietin or cause polycythemia; if anything, anti-angiogenic therapy does not increase red cell mass.
10. A patient on bevacizumab for metastatic colorectal cancer is scheduled for elective colostomy reversal. Regarding perioperative management of bevacizumab, which approach is correct?
A) Hold bevacizumab for at least 28 days before elective surgery and do not resume until at least 28 days after surgery with complete wound healing confirmed, because bevacizumab impairs the VEGF-A-dependent angiogenesis required for wound healing
B) Continue bevacizumab through the perioperative period because it accelerates wound healing
C) Hold bevacizumab only on the day of surgery and resume the next day
D) Stop bevacizumab permanently because any surgery is an absolute contraindication to further therapy
E) Give an extra loading dose of bevacizumab immediately before surgery to protect the anastomosis
ANSWER: A
Rationale:
VEGF-A is required for the new blood vessel formation that supports wound healing. Bevacizumab impairs this process, raising the risk of wound dehiscence, anastomotic leak, and non-healing wounds. The standard rule is to hold bevacizumab at least 28 days before elective surgery and not resume until at least 28 days afterward, once complete wound healing is confirmed.
Option B: Option B is incorrect because bevacizumab impairs rather than accelerates wound healing.
Option C: Option C is incorrect because a single-day hold is far too short given the antibody's long half-life (approximately 20 days) and the prolonged anti-angiogenic effect.
Option D: Option D is incorrect because surgery is not an absolute permanent contraindication; therapy can resume after adequate healing.
Option E: Option E is incorrect because additional bevacizumab around surgery would worsen, not protect, anastomotic healing.
11. An oncologist is considering adding bevacizumab to platinum-based chemotherapy for non-small cell lung cancer (NSCLC). The pathology report is reviewed before prescribing. In which histologic setting is bevacizumab contraindicated?
A) Adenocarcinoma of the lung
B) Large-cell carcinoma of the lung
C) Non-squamous NSCLC with a peripheral tumor location
D) Adenosquamous carcinoma with a predominant glandular component
E) Squamous cell histology, because of the risk of catastrophic pulmonary hemorrhage (hemoptysis) from tumor cavitation
ANSWER: E
Rationale:
Bevacizumab is contraindicated in squamous cell NSCLC because of the risk of fatal pulmonary hemorrhage from tumor cavitation; the pivotal ECOG (Eastern Cooperative Oncology Group) 4599 trial excluded squamous histology for this reason.
Option A: Option A is incorrect because adenocarcinoma is a non-squamous histology in which bevacizumab is permitted with chemotherapy.
Option B: Option B is incorrect because large-cell carcinoma is also non-squamous and not the contraindicated subtype.
Option C: Option C is incorrect because non-squamous NSCLC is the appropriate population for bevacizumab; tumor location is not the deciding factor.
Option D: Option D is incorrect because the contraindication is driven specifically by squamous histology and its bleeding risk; a predominantly glandular adenosquamous tumor is not the classic contraindicated setting, whereas squamous histology clearly is.
12. Before prescribing cetuximab or panitumumab (anti-EGFR antibodies; EGFR is the epidermal growth factor receptor) for metastatic colorectal cancer, a companion diagnostic test is mandatory. Which biomarker result is required for these antibodies to provide benefit?
A) Microsatellite instability-high (MSI-H) status
B) Wild-type RAS (rat sarcoma proto-oncogene) status, because any activating RAS mutation constitutively activates downstream signaling and bypasses EGFR blockade, eliminating benefit
C) HER2 (human epidermal growth factor receptor 2) amplification
D) High programmed death-ligand 1 (PD-L1) expression
E) An activating RAS mutation, which predicts an enhanced response to anti-EGFR therapy
ANSWER: B
Rationale:
Anti-EGFR antibodies require wild-type RAS status to be effective. An activating RAS mutation (KRAS or NRAS, exons 2, 3, or 4) constitutively turns on the downstream RAS/MAPK pathway independent of the receptor, so blocking EGFR no longer suppresses signaling and the patient derives no benefit. Extended RAS testing is therefore mandatory before prescribing.
Option A: Option A is incorrect because MSI-H status guides immune checkpoint inhibitor use, not anti-EGFR antibody eligibility.
Option C: Option C is incorrect because HER2 amplification gates HER2-directed therapy, not anti-EGFR therapy.
Option D: Option D is incorrect because PD-L1 expression guides checkpoint inhibitors, not cetuximab or panitumumab.
Option E: Option E is incorrect because it inverts the truth: a RAS mutation predicts lack of benefit, not enhanced response, and mandates exclusion from anti-EGFR therapy.
13. A patient on cetuximab develops hypomagnesemia (low serum magnesium) with neuromuscular irritability. This electrolyte disturbance is characteristic of anti-EGFR (epidermal growth factor receptor) antibodies but not of small-molecule EGFR tyrosine kinase inhibitors used at equivalent target coverage. What is the mechanism?
A) Increased renal magnesium reabsorption causing a paradoxical intracellular shift
B) Gastrointestinal magnesium malabsorption from antibody-induced mucositis
C) EGFR blockade reduces expression of the TRPM6 (transient receptor potential melastatin 6) magnesium channel in the distal convoluted tubule, impairing active renal magnesium reabsorption and causing renal magnesium wasting
D) Chelation of magnesium by the antibody in the bloodstream
E) Suppression of parathyroid hormone leading to reduced magnesium retention
ANSWER: C
Rationale:
Active magnesium reabsorption in the distal convoluted tubule depends on the TRPM6 channel, whose expression is EGFR-dependent. Blocking EGFR with cetuximab or panitumumab downregulates TRPM6, impairing renal magnesium reabsorption and causing renal magnesium wasting; serum magnesium must be monitored before each cycle and repleted.
Option A: Option A is incorrect because the defect is reduced renal reabsorption (wasting), not increased reabsorption with an intracellular shift.
Option B: Option B is incorrect because the dominant mechanism is renal wasting via TRPM6 downregulation, not gastrointestinal malabsorption.
Option D: Option D is incorrect because the antibody does not chelate magnesium in plasma.
Option E: Option E is incorrect because the mechanism is loss of EGFR-dependent tubular reabsorption, not parathyroid hormone suppression.
14. A patient in the southeastern United States experiences a severe first-infusion hypersensitivity reaction to cetuximab. The reaction is attributed to pre-existing immunoglobulin E (IgE) antibodies. Which explanation is correct, and which related antibody lacks this specific risk?
A) Cetuximab carries the galactose-alpha-1,3-galactose (alpha-gal) sugar epitope from its murine cell-line production, against which some patients have pre-existing IgE (often from prior tick-bite sensitization), causing true IgE-mediated reactions; panitumumab, produced in a non-murine cell line, lacks this epitope and has a much lower severe reaction rate
B) Cetuximab reactions are caused by complement depletion, and panitumumab causes identical reactions
C) The reaction reflects tumor lysis syndrome, and panitumumab carries the same risk
D) The reaction is due to cytokine release alone with no IgE involvement, and panitumumab is more reactive
E) The reaction results from anti-drug antibodies against the human framework region, equally present with panitumumab
ANSWER: A
Rationale:
Cetuximab is produced in a murine cell line and carries the galactose-alpha-1,3-galactose (alpha-gal) epitope on its Fc region. Some patients, particularly in regions with lone-star tick exposure, have pre-existing IgE against alpha-gal, producing true IgE-mediated hypersensitivity reactions that cluster geographically. Panitumumab, made in a non-murine cell line, lacks the alpha-gal epitope and has a substantially lower severe infusion reaction rate.
Option B: Option B is incorrect because the mechanism is pre-formed IgE against alpha-gal, not complement depletion, and panitumumab does not share the risk.
Option C: Option C is incorrect because this is hypersensitivity, not tumor lysis syndrome.
Option D: Option D is incorrect because the cetuximab reactions in this setting are specifically IgE-mediated, and panitumumab is less, not more, reactive.
Option E: Option E is incorrect because the culprit antigen is the alpha-gal carbohydrate, not the human framework region, and panitumumab does not carry the same risk.
15. A patient with B-cell non-Hodgkin lymphoma is about to start rituximab, an anti-CD20 (a B-cell surface antigen) monoclonal antibody. Which screening step is mandatory before initiating therapy because of a potentially fatal reactivation risk?
A) Screening for latent tuberculosis with an interferon-gamma release assay before the first dose
B) Baseline pulmonary function testing to detect early interstitial lung disease
C) Screening for glucose-6-phosphate dehydrogenase deficiency to prevent hemolysis
D) Screening for hepatitis B (HBsAg, hepatitis B surface antigen, and HBcAb, hepatitis B core antibody), because B-cell depletion can trigger hepatitis B virus reactivation, which may cause fulminant hepatic failure
E) Screening for UGT1A1 (uridine diphosphate-glucuronosyltransferase 1A1) genotype to avoid severe neutropenia
ANSWER: D
Rationale:
Rituximab-mediated B-cell depletion removes immune control of hepatitis B virus, so reactivation is a recognized and potentially fatal complication. All patients must be screened for HBsAg and HBcAb before starting therapy: HBsAg-positive patients require antiviral prophylaxis (entecavir or tenofovir), and HBcAb-positive/HBsAg-negative patients require prophylaxis or close monitoring.
Option A: Option A is incorrect because tuberculosis screening, while relevant for certain other biologics, is not the defining mandatory pre-rituximab reactivation screen.
Option B: Option B is incorrect because baseline pulmonary function testing is not the mandated screen tied to rituximab's reactivation risk.
Option C: Option C is incorrect because glucose-6-phosphate dehydrogenase screening is unrelated to rituximab.
Option E: Option E is incorrect because UGT1A1 genotyping pertains to sacituzumab govitecan and SN-38 toxicity, not to rituximab.
16. After a standard course of rituximab, a patient's circulating B cells are depleted, yet pre-existing serum immunoglobulin levels are relatively preserved. Which feature of CD20 (the rituximab target antigen) expression best explains this observation?
A) Rituximab selectively spares memory B cells, which sustain immunoglobulin production
B) Rituximab upregulates immunoglobulin synthesis in surviving B cells
C) CD20 is expressed only on T cells, so B-cell immunoglobulin production is unaffected
D) Rituximab is rapidly cleared before it can deplete antibody-secreting cells
E) CD20 is expressed from the pre-B cell through the mature B cell stage but is absent on plasma cells, so the antibody-secreting plasma cell population that produces immunoglobulin is not directly targeted
ANSWER: E
Rationale:
CD20 is present from the pre-B cell stage through the mature B cell stage but is absent on terminally differentiated plasma cells. Because plasma cells are the principal antibody-secreting population and they do not express CD20, rituximab depletes B cells while leaving existing immunoglobulin production relatively preserved.
Option A: Option A is incorrect because the explanation is the absence of CD20 on plasma cells, not selective sparing of memory B cells (which do express CD20 and are depleted).
Option B: Option B is incorrect because rituximab does not upregulate immunoglobulin synthesis.
Option C: Option C is incorrect because CD20 is a B-cell antigen, not a T-cell antigen.
Option D: Option D is incorrect because rituximab has a long half-life (approximately 22 days) and produces prolonged B-cell depletion; rapid clearance is not the reason immunoglobulin is preserved.
17. A patient with multiple myeloma is starting daratumumab, an anti-CD38 (cyclic ADP-ribose hydrolase) monoclonal antibody. The blood bank must be notified before the first dose. What is the basis for this requirement?
A) Daratumumab causes hemolysis that requires frequent transfusion of irradiated blood products
B) Daratumumab binds CD38 on red blood cells, producing pan-reactive false-positive indirect antiglobulin (indirect Coombs) tests that can mask clinically significant alloantibodies and complicate pre-transfusion compatibility testing
C) Daratumumab depletes platelets, requiring prophylactic platelet transfusions before each dose
D) Daratumumab alters the patient's ABO blood type, requiring repeat typing before every transfusion
E) Daratumumab binds donor red cells in transfused units, causing immediate transfusion reactions unrelated to laboratory testing
ANSWER: B
Rationale:
CD38 is expressed at low levels on red blood cells. Daratumumab binds these cells and causes pan-reactive false-positive indirect antiglobulin tests (indirect Coombs tests) that can persist for up to 6 months after the last dose, masking true alloantibodies against donor antigens. The blood bank must be informed before the first dose so that baseline typing and antibody screening are recorded and special techniques (such as dithiothreitol treatment of reagent cells) are used for future compatibility testing.
Option A: Option A is incorrect because the issue is laboratory test interference, not clinically significant hemolysis requiring irradiated products.
Option C: Option C is incorrect because the concern is interference with crossmatching, not daratumumab-induced thrombocytopenia.
Option D: Option D is incorrect because daratumumab does not change the patient's ABO type; it interferes with the antibody screen.
Option E: Option E is incorrect because the antibody binds the patient's own CD38-bearing red cells and disrupts testing, rather than causing direct reactions against transfused units.
18. A patient with bone metastases is starting denosumab, a monoclonal antibody against RANKL (receptor activator of nuclear factor kappa-B ligand) used to reduce skeletal-related events. Which co-intervention is mandatory to prevent a common and potentially serious metabolic toxicity?
A) Co-supplementation with calcium and vitamin D throughout therapy, because denosumab's potent suppression of osteoclast-mediated bone resorption can produce hypocalcemia
B) Routine potassium supplementation to prevent denosumab-induced hypokalemia
C) Prophylactic phosphate binders to prevent hyperphosphatemia
D) Daily oral magnesium to counteract denosumab-induced renal magnesium wasting
E) Scheduled iron infusions to prevent denosumab-associated anemia
ANSWER: A
Rationale:
Denosumab blocks the RANKL-RANK interaction, profoundly suppressing osteoclast differentiation and bone resorption. Because resorption normally releases calcium into the circulation, this potent suppression can cause hypocalcemia (roughly 10 to 18 percent of patients), more often than with bisphosphonates. Mandatory co-supplementation with calcium and vitamin D is required, and pre-existing hypocalcemia must be corrected before starting.
Option B: Option B is incorrect because denosumab does not cause clinically important hypokalemia.
Option C: Option C is incorrect because hyperphosphatemia requiring phosphate binders is not a characteristic denosumab toxicity.
Option D: Option D is incorrect because renal magnesium wasting is the hallmark of anti-EGFR antibodies (via TRPM6 downregulation), not denosumab.
Option E: Option E is incorrect because denosumab is not associated with an anemia requiring scheduled iron infusions.
19. Two HER2-directed antibody-drug conjugates (ADCs, antibodies linked to a cytotoxic payload) differ in their linker chemistry: trastuzumab emtansine (T-DM1) uses a non-cleavable linker, whereas trastuzumab deruxtecan (T-DXd) uses a cleavable linker with a membrane-permeable payload. Which statement correctly relates linker type to the bystander effect (killing of neighboring cells that may not express the target)?
A) Both ADCs produce identical, maximal bystander killing regardless of linker type
B) The non-cleavable linker of T-DM1 enhances bystander killing, while the cleavable linker of T-DXd prevents it
C) The non-cleavable linker of T-DM1 yields a charged, membrane-impermeant metabolite that limits bystander killing, whereas the cleavable linker of T-DXd releases a membrane-permeable payload that can diffuse into neighboring cells and produce bystander killing
D) Bystander killing depends only on the drug-to-antibody ratio and is independent of linker chemistry
E) Cleavable linkers release payload only in the bloodstream, so T-DXd has no intracellular activity
ANSWER: C
Rationale:
With a non-cleavable linker, T-DM1 releases its payload only after complete lysosomal degradation of the antibody, producing a charged, membrane-impermeant metabolite that stays within the target cell and limits bystander killing. T-DXd's cleavable linker releases a membrane-permeable payload (a topoisomerase I inhibitor) that can diffuse into adjacent cells, producing bystander killing that contributes to activity in tumors with heterogeneous target expression.
Option A: Option A is incorrect because the two ADCs differ markedly in bystander potential precisely because of linker and payload properties.
Option B: Option B is incorrect because it reverses the relationship: the cleavable, membrane-permeable design (T-DXd) is what enables bystander killing.
Option D: Option D is incorrect because linker chemistry and payload permeability, not drug-to-antibody ratio alone, determine bystander killing.
Option E: Option E is incorrect because cleavable linkers release payload intracellularly after internalization and cleavage, not in the bloodstream, and T-DXd is highly active intracellularly.
20. A patient receiving trastuzumab deruxtecan (T-DXd) reports new dyspnea, and computed tomography shows ground-glass opacities. Which adverse effect is the most serious characteristic toxicity of T-DXd, requiring prompt recognition?
A) Acute kidney injury from antibody deposition in the glomerulus
B) Hemorrhagic cystitis from the cytotoxic payload
C) Severe peripheral neuropathy from microtubule disruption
D) Interstitial lung disease (ILD)/pneumonitis, which requires holding the drug and, depending on grade, corticosteroids or permanent discontinuation
E) Profound hypocalcemia from osteoclast suppression
ANSWER: D
Rationale:
The most serious characteristic toxicity of T-DXd is interstitial lung disease/pneumonitis, with rare fatal cases. It must be recognized promptly: grade 1 (asymptomatic, imaging findings only) prompts holding the drug; grade 2 prompts holding plus systemic corticosteroids; grade 3 or higher prompts permanent discontinuation and high-dose corticosteroids.
Option A: Option A is incorrect because acute kidney injury from glomerular antibody deposition is not the signature T-DXd toxicity.
Option B: Option B is incorrect because hemorrhagic cystitis is associated with agents such as cyclophosphamide, not T-DXd.
Option C: Option C is incorrect because severe peripheral neuropathy is characteristic of MMAE-containing ADCs (brentuximab, polatuzumab), not the topoisomerase I payload of T-DXd.
Option E: Option E is incorrect because profound hypocalcemia is a denosumab effect, not a T-DXd effect.
21. A patient on brentuximab vedotin for Hodgkin lymphoma develops progressive sensory peripheral neuropathy. This dose-limiting toxicity is shared with polatuzumab vedotin but is not expected with antibody-drug conjugates that carry topoisomerase inhibitor payloads. Which payload accounts for this neuropathy?
A) SN-38, the active metabolite of irinotecan
B) Deruxtecan (DXd), a topoisomerase I inhibitor
C) A platinum-based alkylating agent
D) An anthracycline incorporated into the conjugate
E) Monomethyl auristatin E (MMAE), a microtubule polymerization inhibitor that disrupts axonal microtubule dynamics in dorsal root ganglion neurons
ANSWER: E
Rationale:
Brentuximab vedotin and polatuzumab vedotin both carry monomethyl auristatin E (MMAE), a potent microtubule polymerization inhibitor. MMAE disrupts axonal microtubule transport in dorsal root ganglion neurons, producing the dose-limiting sensory peripheral neuropathy characteristic of these agents; this is not expected with topoisomerase inhibitor payloads.
Option A: Option A is incorrect because SN-38 is the payload of sacituzumab govitecan and causes neutropenia and diarrhea rather than the signature neuropathy.
Option B: Option B is incorrect because deruxtecan (DXd) is a topoisomerase I inhibitor associated with interstitial lung disease, not the characteristic MMAE neuropathy.
Option C: Option C is incorrect because these ADCs do not use platinum alkylating payloads.
Option D: Option D is incorrect because the conjugated payload is MMAE, not an anthracycline.
22. A patient with triple-negative breast cancer is being considered for sacituzumab govitecan, an antibody-drug conjugate delivering SN-38 (the active metabolite of irinotecan). Genotyping is recommended before treatment. Which genotype predicts substantially higher risk of severe neutropenia and diarrhea?
A) HER2 (human epidermal growth factor receptor 2) amplification
B) UGT1A1*28 homozygosity (UGT1A1*28/*28), which reduces UGT1A1 (uridine diphosphate-glucuronosyltransferase 1A1) activity and impairs glucuronidation and elimination of SN-38, leading to payload accumulation
C) A BRAF (v-raf murine sarcoma viral oncogene homolog B) V600E mutation
D) Wild-type RAS (rat sarcoma proto-oncogene) status
E) CYP2D6 (cytochrome P450 2D6) ultrarapid metabolizer status
ANSWER: B
Rationale:
SN-38 is detoxified by glucuronidation via UGT1A1. Patients homozygous for the UGT1A1*28 promoter polymorphism (UGT1A1*28/*28) have markedly reduced UGT1A1 activity, impairing SN-38 clearance and producing higher SN-38 exposure; this predicts severe neutropenia and diarrhea, so genotyping is recommended and homozygotes warrant closer monitoring and earlier dose reduction.
Option A: Option A is incorrect because HER2 amplification is a therapy-selection biomarker, not a determinant of SN-38 toxicity.
Option C: Option C is incorrect because a BRAF V600E mutation predicts anti-EGFR resistance in colorectal cancer, not SN-38 toxicity risk.
Option D: Option D is incorrect because wild-type RAS status governs anti-EGFR antibody benefit and does not predict sacituzumab govitecan toxicity.
Option E: Option E is incorrect because SN-38 detoxification depends on UGT1A1 glucuronidation, not CYP2D6 metabolism.
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