Chapter 34 — Anti-Cancer Drugs Part 2 — Module 3 — Monoclonal Antibodies and Antibody-Drug Conjugates
1. A therapeutic monoclonal antibody is observed to be cleared more rapidly, with a shorter effective half-life, when given at low doses, while clearance slows and half-life lengthens at higher doses. Two elimination processes are operating: neonatal Fc receptor (FcRn)-mediated recycling and target-mediated drug disposition. Which statement correctly discriminates their relative contributions to this dose-dependent clearance?
A) FcRn recycling is saturated at low doses and becomes the dominant clearance route only at high doses
B) Target-mediated drug disposition dominates clearance at low, sub-saturating concentrations and produces the faster clearance, whereas once the target is saturated at higher doses, the slower FcRn-governed route predominates and half-life lengthens
C) Both processes contribute equally and independently of concentration, so clearance is linear across all doses
D) Target-mediated drug disposition is negligible at all concentrations because antibody-target binding does not lead to elimination
E) FcRn recycling accelerates clearance at low doses by routing the antibody to lysosomal degradation
ANSWER: B
Rationale:
Target-mediated drug disposition (TMDD) is a saturable, high-affinity elimination route: at low, sub-saturating concentrations it rapidly clears the antibody via receptor-mediated endocytosis of the antibody-target complex, producing fast clearance and a short effective half-life. Once the target is saturated at higher doses, this route contributes proportionally less and the slower FcRn-governed recycling pathway predominates, lengthening half-life.
Option A: Option A is incorrect because FcRn recycling is a salvage pathway that protects antibody from degradation; it is not the saturable route responsible for fast low-dose clearance, and target-mediated clearance, not FcRn, is saturated as dose rises.
Option C: Option C is incorrect because the clearance is demonstrably nonlinear (dose-dependent), not linear.
Option D: Option D is incorrect because antibody-target binding followed by complex internalization is precisely the elimination mechanism of TMDD.
Option E: Option E is incorrect because FcRn binding in acidic endosomes rescues antibody from lysosomal degradation and recycles it to the circulation, slowing rather than accelerating clearance.
2. Trastuzumab and pertuzumab are both anti-HER2 (human epidermal growth factor receptor 2) monoclonal antibodies used together for dual HER2 blockade, yet they bind distinct epitopes and exert distinct primary effects. Which pairing correctly discriminates their binding sites and dominant mechanisms?
A) Trastuzumab binds domain IV and blocks extracellular-domain cleavage and downstream signaling; pertuzumab binds domain II and blocks HER2 dimerization, particularly the HER2-HER3 heterodimer
B) Trastuzumab binds domain II and blocks dimerization; pertuzumab binds domain IV and blocks extracellular-domain cleavage
C) Both antibodies bind domain IV and differ only in the immunoglobulin subclass of their Fc region
D) Trastuzumab binds the intracellular tyrosine kinase domain; pertuzumab binds domain IV
E) Both antibodies bind domain II and act primarily by neutralizing the HER2 ligand
ANSWER: A
Rationale:
Trastuzumab binds domain IV of the HER2 extracellular domain, sterically blocking cleavage that would release the constitutively active p95-HER2 fragment and inhibiting downstream signaling. Pertuzumab binds a different epitope, domain II, and blocks HER2 from dimerizing with other ErbB-family receptors, particularly the potent HER2-HER3 heterodimer.
Option B: Option B is incorrect because it reverses the two epitopes.
Option C: Option C is incorrect because the antibodies bind different domains (IV versus II); they do not both bind domain IV.
Option D: Option D is incorrect because trastuzumab is an antibody acting on the extracellular domain IV, not the intracellular kinase domain.
Option E: Option E is incorrect because HER2 has no known direct ligand to neutralize, and the two antibodies bind different domains rather than both binding domain II.
3. A patient who received an anthracycline (doxorubicin) and later trastuzumab is evaluated for cardiac dysfunction. The two agents cause cardiotoxicity by mechanistically distinct routes with different reversibility. Which statement correctly discriminates anthracycline from trastuzumab cardiotoxicity?
A) Both produce irreversible, cumulative, dose-dependent cardiomyopathy through identical free-radical mechanisms
B) Anthracycline cardiotoxicity is reversible on discontinuation, whereas trastuzumab cardiotoxicity is permanent and dose-dependent
C) Anthracycline cardiotoxicity is free-radical-mediated, cumulative, dose-dependent, and largely irreversible, whereas trastuzumab cardiotoxicity reflects blockade of HER2/HER4 cardiac repair signaling, is generally not dose-dependent, and is largely reversible after the drug is held
D) Trastuzumab cardiotoxicity is caused by direct mitochondrial DNA damage, and anthracycline cardiotoxicity is caused by impaired repair signaling
E) Neither agent requires left ventricular ejection fraction monitoring because cardiotoxicity is rare and clinically insignificant
ANSWER: C
Rationale:
Anthracycline cardiotoxicity results from free-radical-mediated injury to cardiomyocyte mitochondria and DNA; it is cumulative, dose-dependent, and largely irreversible. Trastuzumab cardiotoxicity results from blockade of HER2/HER4 (ErbB) cardiac stress-response and repair signaling; it is generally not dose-dependent and is largely reversible after holding the drug.
Option A: Option A is incorrect because the two mechanisms and their reversibility differ; they are not identical free-radical processes.
Option B: Option B is incorrect because it reverses the reversibility profiles.
Option D: Option D is incorrect because it swaps the mechanisms: free-radical mitochondrial/DNA damage is the anthracycline mechanism, and impaired repair signaling is the trastuzumab mechanism.
Option E: Option E is incorrect because left ventricular ejection fraction monitoring is mandatory with trastuzumab, with defined hold thresholds, precisely because the cardiotoxicity is clinically significant.
4. Trastuzumab emtansine (T-DM1) and trastuzumab deruxtecan (T-DXd) are both HER2-directed antibody-drug conjugates, but they differ in linker chemistry and payload properties, which determines whether they produce a bystander effect (killing of adjacent cells that may not express the target). Which statement correctly discriminates the two?
A) T-DM1 uses a cleavable linker releasing a membrane-permeable payload and produces strong bystander killing; T-DXd uses a non-cleavable linker and produces none
B) Both conjugates use non-cleavable linkers, so neither produces bystander killing
C) Both conjugates produce equally strong bystander killing because they share the same antibody backbone
D) T-DM1 uses a non-cleavable linker yielding a charged, membrane-impermeant metabolite that limits bystander killing, whereas T-DXd uses a cleavable linker releasing a membrane-permeable topoisomerase I inhibitor payload that diffuses into neighboring cells and produces bystander killing
E) The bystander effect depends solely on the trastuzumab antibody component and is identical for both conjugates
ANSWER: D
Rationale:
T-DM1 employs a non-cleavable linker; its payload is released only after complete lysosomal degradation of the antibody, producing a charged, membrane-impermeant metabolite that remains within the target cell and limits bystander killing. T-DXd employs a cleavable linker that releases a membrane-permeable topoisomerase I inhibitor payload, which can diffuse into adjacent cells and produce bystander killing—useful in tumors with heterogeneous HER2 expression.
Option A: Option A is incorrect because it reverses the linker assignments.
Option B: Option B is incorrect because only T-DM1 is non-cleavable; T-DXd is cleavable.
Option C: Option C is incorrect because the shared antibody backbone does not equalize bystander killing, which is governed by linker and payload permeability.
Option E: Option E is incorrect because the bystander effect depends on the released payload's membrane permeability, not the antibody component.
5. Cetuximab and panitumumab are both anti-EGFR (epidermal growth factor receptor) antibodies approved in metastatic colorectal cancer, but they differ in molecular construction and in their severe infusion reaction risk. Which statement correctly discriminates the two agents?
A) Cetuximab is a fully human IgG2 antibody and panitumumab is a chimeric IgG1 antibody, so cetuximab has the lower infusion reaction rate
B) Both are chimeric IgG1 antibodies and carry an identical risk of galactose-alpha-1,3-galactose-mediated reactions
C) Panitumumab is a chimeric antibody bearing the galactose-alpha-1,3-galactose epitope, accounting for its higher severe infusion reaction rate
D) Both are fully human antibodies, so neither carries any infusion reaction risk
E) Cetuximab is a chimeric IgG1 antibody whose murine-derived galactose-alpha-1,3-galactose epitope predisposes to immunoglobulin E-mediated infusion reactions, whereas panitumumab is a fully human IgG2 antibody that lacks this epitope and has a substantially lower severe infusion reaction rate
ANSWER: E
Rationale:
Cetuximab is a chimeric IgG1 antibody produced in a murine cell line; it carries the galactose-alpha-1,3-galactose (alpha-gal) epitope, against which some patients have pre-existing immunoglobulin E, predisposing to true IgE-mediated infusion reactions. Panitumumab is a fully human IgG2 antibody produced in a non-murine cell line; it lacks the alpha-gal epitope and has a substantially lower rate of severe infusion reactions.
Option A: Option A is incorrect because it reverses the constructions (cetuximab is chimeric IgG1; panitumumab is fully human IgG2).
Option B: Option B is incorrect because the two are not both chimeric and do not share identical alpha-gal risk.
Option C: Option C is incorrect because it misattributes the chimeric, alpha-gal-bearing construction to panitumumab rather than cetuximab.
Option D: Option D is incorrect because cetuximab is chimeric, not fully human, and infusion reaction risk is not zero for these agents.
6. Rituximab is a type I anti-CD20 antibody and obinutuzumab is a glycoengineered type II anti-CD20 antibody. They deplete B cells through overlapping but distinct dominant mechanisms. Which statement correctly discriminates the two?
A) Rituximab (type I) drives CD20 into lipid rafts and produces strong complement-dependent cytotoxicity, whereas obinutuzumab (type II) does not induce this lipid-raft redistribution and instead has enhanced direct cell death and, through Fc glycoengineering, markedly greater antibody-dependent cellular cytotoxicity
B) Obinutuzumab (type I) produces strong complement-dependent cytotoxicity via lipid-raft redistribution, whereas rituximab (type II) relies on direct cell death
C) Both antibodies are non-glycoengineered and produce identical complement-dependent cytotoxicity
D) Rituximab is glycoengineered for enhanced antibody-dependent cellular cytotoxicity, whereas obinutuzumab is not engineered and acts only through complement
E) Neither antibody engages Fc-receptor-bearing effector cells; both act exclusively through direct apoptosis
ANSWER: A
Rationale:
Rituximab is a type I anti-CD20 antibody that redistributes CD20 into lipid rafts, a process that supports robust complement-dependent cytotoxicity. Obinutuzumab is a type II antibody that does not induce lipid-raft redistribution and therefore relies less on complement; it has enhanced direct cell death induction and, owing to Fc glycoengineering, markedly greater antibody-dependent cellular cytotoxicity via increased affinity for the Fc gamma receptor on effector cells.
Option B: Option B is incorrect because it swaps the type I and type II designations and their mechanisms.
Option C: Option C is incorrect because obinutuzumab is glycoengineered and the two do not share identical complement activity.
Option D: Option D is incorrect because it is obinutuzumab, not rituximab, that is glycoengineered for enhanced antibody-dependent cellular cytotoxicity.
Option E: Option E is incorrect because both antibodies engage Fc-receptor-bearing effector cells through antibody-dependent cellular cytotoxicity in addition to other mechanisms.
7. A patient on bevacizumab develops proteinuria detected on routine pre-cycle urinalysis, prompting 24-hour urine protein quantification. Bevacizumab management distinguishes a threshold for holding the drug from a threshold for permanent discontinuation. Which pairing is correct?
A) Hold for proteinuria exceeding 0.5 g/24 hours; permanently discontinue for proteinuria exceeding 1 g/24 hours
B) Hold bevacizumab for proteinuria exceeding 2 g/24 hours; permanently discontinue for nephrotic-range proteinuria exceeding 3.5 g/24 hours
C) Continue bevacizumab regardless of proteinuria because anti-VEGF therapy does not affect the kidney
D) Permanently discontinue bevacizumab at the first detection of any dipstick-positive proteinuria
E) Hold bevacizumab only when proteinuria exceeds 10 g/24 hours; lesser values require no action
ANSWER: B
Rationale:
Bevacizumab impairs vascular endothelial growth factor A-dependent maintenance of glomerular podocyte function, producing proteinuria. Management holds the drug for proteinuria exceeding 2 g/24 hours and permanently discontinues it for nephrotic-range proteinuria exceeding 3.5 g/24 hours; urinalysis is performed before each cycle with 24-hour quantification when dipstick is 2+ or higher.
Option A: Option A is incorrect because the hold and discontinuation thresholds are 2 g and 3.5 g/24 hours, not 0.5 g and 1 g.
Option C: Option C is incorrect because anti-VEGF therapy clearly produces proteinuria and requires monitoring and action.
Option D: Option D is incorrect because a single dipstick-positive result triggers quantification, not automatic permanent discontinuation.
Option E: Option E is incorrect because the hold threshold is 2 g/24 hours, far below 10 g, and lesser elevations do require monitoring and action.
8. A patient on panitumumab develops persistent hypomagnesemia requiring repletion. This electrolyte disturbance is specific to anti-EGFR (epidermal growth factor receptor) antibodies. Which mechanism correctly identifies the site and process, discriminating it from other causes of hypomagnesemia?
A) Increased aldosterone-driven magnesium excretion in the collecting duct
B) Proximal tubular magnesium wasting from inhibition of the sodium-glucose cotransporter
C) Reduced expression of the TRPM6 (transient receptor potential melastatin 6) magnesium channel in the distal convoluted tubule, because epidermal growth factor receptor signaling normally maintains TRPM6-mediated active magnesium reabsorption; blockade causes renal magnesium wasting
D) Sequestration of magnesium into bone driven by enhanced osteoblast activity
E) Gastrointestinal magnesium loss from antibody-induced secretory diarrhea
ANSWER: C
Rationale:
Active magnesium reabsorption in the distal convoluted tubule occurs through the TRPM6 channel, whose expression is epidermal growth factor receptor-dependent. Anti-EGFR antibodies downregulate TRPM6, impairing distal magnesium reabsorption and producing renal magnesium wasting; serum magnesium is monitored before each cycle and repleted.
Option A: Option A is incorrect because the defect is loss of TRPM6-mediated distal reabsorption, not aldosterone-driven collecting-duct excretion.
Option B: Option B is incorrect because the affected transporter is the distal TRPM6 channel, not a proximal sodium-glucose cotransporter.
Option D: Option D is incorrect because the mechanism is renal wasting, not skeletal sequestration.
Option E: Option E is incorrect because the dominant mechanism is renal, not gastrointestinal, magnesium loss.
9. Antibody-drug conjugates carry payloads whose signature toxicities differ by payload class. A clinician must match the dominant characteristic toxicity to the correct payload. Which matching is correct?
A) Monomethyl auristatin E (a microtubule inhibitor) -> interstitial lung disease; deruxtecan (a topoisomerase I inhibitor) -> peripheral neuropathy
B) SN-38 (the active metabolite of irinotecan) -> peripheral neuropathy; monomethyl auristatin E -> interstitial lung disease
C) Deruxtecan -> hemorrhagic cystitis; SN-38 -> peripheral neuropathy
D) Deruxtecan (a topoisomerase I inhibitor) -> interstitial lung disease/pneumonitis; monomethyl auristatin E (a microtubule inhibitor) -> peripheral neuropathy; SN-38 (a topoisomerase I inhibitor) -> neutropenia and diarrhea
E) All three payloads produce identical dose-limiting peripheral neuropathy
ANSWER: D
Rationale:
Each payload class has a signature toxicity. Deruxtecan, the topoisomerase I inhibitor payload of trastuzumab deruxtecan, is associated with interstitial lung disease/pneumonitis. Monomethyl auristatin E, a microtubule polymerization inhibitor (in brentuximab vedotin and polatuzumab vedotin), produces peripheral neuropathy through axonal microtubule disruption. SN-38, the topoisomerase I inhibitor payload of sacituzumab govitecan, produces neutropenia and diarrhea.
Option A: Option A is incorrect because it swaps the microtubule-inhibitor and topoisomerase-inhibitor toxicities.
Option B: Option B is incorrect because SN-38 causes neutropenia and diarrhea rather than neuropathy, and monomethyl auristatin E causes neuropathy rather than interstitial lung disease.
Option C: Option C is incorrect because deruxtecan does not cause hemorrhagic cystitis and SN-38 does not cause peripheral neuropathy.
Option E: Option E is incorrect because the three payloads produce distinct, not identical, dose-limiting toxicities.
10. Brentuximab vedotin and polatuzumab vedotin share the same cytotoxic payload and linker chemistry but target different surface antigens on different malignancies. Which statement correctly discriminates their targets while recognizing their shared payload?
A) Both deliver monomethyl auristatin E via a protease-cleavable valine-citrulline linker, but brentuximab vedotin targets CD30 on Hodgkin lymphoma and systemic anaplastic large cell lymphoma, whereas polatuzumab vedotin targets CD79b (a B-cell receptor signaling subunit) on B-cell non-Hodgkin lymphomas such as diffuse large B-cell lymphoma
B) Both target CD30 but deliver different payloads, accounting for their different indications
C) Brentuximab vedotin targets CD79b on diffuse large B-cell lymphoma, and polatuzumab vedotin targets CD30 on Hodgkin lymphoma
D) Both deliver a topoisomerase I inhibitor payload and target CD20 on B-cell lymphomas
E) The two agents have identical targets and differ only in their drug-to-antibody ratio
ANSWER: A
Rationale:
Both brentuximab vedotin and polatuzumab vedotin deliver monomethyl auristatin E through a protease-cleavable valine-citrulline linker, which is why they share peripheral neuropathy and myelosuppression as toxicities. They differ in target: brentuximab vedotin targets CD30, highly expressed on Reed-Sternberg cells in classical Hodgkin lymphoma and on systemic anaplastic large cell lymphoma, whereas polatuzumab vedotin targets CD79b, a B-cell receptor signaling subunit on B-cell non-Hodgkin lymphomas including diffuse large B-cell lymphoma.
Option B: Option B is incorrect because they share the same payload rather than differing in payload, and they do not both target CD30.
Option C: Option C is incorrect because it swaps the two targets.
Option D: Option D is incorrect because the payload is monomethyl auristatin E, not a topoisomerase I inhibitor, and neither targets CD20.
Option E: Option E is incorrect because the targets are distinct (CD30 versus CD79b), not identical.
11. A patient being considered for sacituzumab govitecan undergoes pharmacogenomic genotyping. The relevant gene governs detoxification of the SN-38 payload (the active metabolite of irinotecan). Which statement correctly identifies the gene, the affected reaction, and the consequence?
A) CYP3A4 genotype determines SN-38 oxidation; poor metabolizers clear SN-38 faster and need higher doses
B) The TPMT (thiopurine methyltransferase) genotype governs SN-38 methylation; deficiency causes reduced efficacy
C) The DPYD (dihydropyrimidine dehydrogenase) genotype governs SN-38 catabolism; deficiency causes neurotoxicity
D) The UGT1A1*28 polymorphism increases UGT1A1 activity, accelerating SN-38 clearance and reducing toxicity
E) UGT1A1*28 homozygosity reduces UGT1A1 (uridine diphosphate-glucuronosyltransferase 1A1) activity, impairing glucuronidation of SN-38; the resulting accumulation predicts severe neutropenia and diarrhea, so dose reduction and closer monitoring are warranted
ANSWER: E
Rationale:
SN-38 is detoxified by glucuronidation through UGT1A1. The UGT1A1*28 promoter polymorphism reduces UGT1A1 expression; homozygotes (UGT1A1*28/*28) have markedly reduced activity, impairing SN-38 glucuronidation and clearance. The resulting SN-38 accumulation predicts severe neutropenia and diarrhea, so genotyping is recommended and homozygotes warrant dose reduction and closer monitoring.
Option A: Option A is incorrect because SN-38 detoxification is by UGT1A1 glucuronidation, not CYP3A4 oxidation.
Option B: Option B is incorrect because thiopurine methyltransferase governs thiopurine metabolism, not SN-38.
Option C: Option C is incorrect because dihydropyrimidine dehydrogenase governs fluoropyrimidine catabolism, not SN-38.
Option D: Option D is incorrect because the UGT1A1*28 allele reduces, not increases, UGT1A1 activity, raising rather than lowering toxicity risk.
12. A patient on daratumumab has a newly positive antibody screen on pre-transfusion testing, but no clinical evidence of hemolysis. The blood bank reports a pan-reactive indirect antiglobulin (indirect Coombs) test. Which statement correctly discriminates the cause and its clinical significance?
A) The finding reflects acute intravascular hemolysis caused by daratumumab binding donor red cells, requiring immediate transfusion cessation
B) Daratumumab binds CD38 on the patient's red blood cells, producing a pan-reactive false-positive indirect antiglobulin test that is laboratory interference rather than true hemolysis; the danger is that it can mask clinically significant alloantibodies, so the blood bank must use special techniques such as dithiothreitol-treated reagent cells
C) The positive screen indicates a new ABO incompatibility caused by daratumumab altering the patient's blood group antigens
D) The result reflects delayed hemolytic transfusion reaction and mandates permanent avoidance of all future transfusion
E) The finding is clinically meaningless and requires no communication with the blood bank
ANSWER: B
Rationale:
Daratumumab binds CD38 expressed at low levels on red blood cells, producing a pan-reactive false-positive indirect antiglobulin test. This is laboratory interference, not true hemolysis; its danger is that it can mask clinically significant alloantibodies and compromise safe crossmatching. The blood bank must be notified and use special techniques (such as dithiothreitol treatment of reagent cells) for compatibility testing, and baseline typing and screening should be recorded before the first dose.
Option A: Option A is incorrect because the phenomenon is test interference, not intravascular hemolysis.
Option C: Option C is incorrect because daratumumab does not change the patient's ABO antigens.
Option D: Option D is incorrect because this is not a delayed hemolytic transfusion reaction and does not mandate permanent transfusion avoidance.
Option E: Option E is incorrect because the interference is clinically important and requires explicit blood bank communication to prevent masking of true alloantibodies.
13. For bone metastases, denosumab (an anti-RANKL [receptor activator of nuclear factor kappa-B ligand] antibody) is sometimes chosen over a bisphosphonate. Which statement correctly discriminates denosumab from a bisphosphonate with respect to elimination and a key toxicity?
A) Denosumab is renally eliminated and is contraindicated in renal impairment, whereas bisphosphonates are not renally cleared
B) Denosumab and bisphosphonates are both renally cleared and carry identical hypocalcemia risk
C) Denosumab does not undergo renal elimination, so it can be used where bisphosphonates are limited by renal impairment, but its more complete osteoclast suppression makes hypocalcemia more likely, mandating calcium and vitamin D co-supplementation
D) Denosumab works by incorporating into bone mineral like a bisphosphonate and shares an identical mechanism
E) Denosumab carries no risk of osteonecrosis of the jaw, unlike bisphosphonates
ANSWER: C
Rationale:
Denosumab is a monoclonal antibody that is catabolized like other antibodies and does not depend on renal elimination, unlike bisphosphonates, so it can be used when renal impairment limits bisphosphonate use. However, its more complete suppression of osteoclast-mediated bone resorption makes hypocalcemia more likely than with bisphosphonates, so calcium and vitamin D co-supplementation is mandatory.
Option A: Option A is incorrect because denosumab is not renally eliminated; that is the property of bisphosphonates.
Option B: Option B is incorrect because denosumab is not renally cleared and its hypocalcemia risk is greater, not identical.
Option D: Option D is incorrect because denosumab blocks the RANKL-RANK interaction rather than incorporating into bone mineral.
Option E: Option E is incorrect because denosumab does carry a risk of osteonecrosis of the jaw, particularly with long-term high-dose therapy.
14. The drug-to-antibody ratio (the average number of payload molecules per antibody) differs between trastuzumab emtansine (T-DM1) and trastuzumab deruxtecan (T-DXd), and this difference, together with payload properties, underlies T-DXd activity in HER2-low (low-level HER2-expressing) tumors. Which statement correctly discriminates the two and links the difference to clinical activity?
A) T-DM1 has a drug-to-antibody ratio of approximately 3.5, whereas T-DXd has a higher ratio of approximately 8; the higher ratio combined with a membrane-permeable payload capable of bystander killing produces potent activity even at low HER2 expression, supporting the HER2-low indication
B) T-DM1 has a higher drug-to-antibody ratio than T-DXd, which is why T-DM1 is the agent active in HER2-low disease
C) Both conjugates have a drug-to-antibody ratio of approximately 8 and identical activity in HER2-low tumors
D) The drug-to-antibody ratio is irrelevant to potency; only the antibody affinity determines activity in HER2-low tumors
E) T-DXd has a lower drug-to-antibody ratio than T-DM1, which limits its activity to HER2-positive disease only
ANSWER: A
Rationale:
T-DM1 has a drug-to-antibody ratio of approximately 3.5, whereas T-DXd has a higher ratio of approximately 8. The higher payload load, combined with a membrane-permeable topoisomerase I inhibitor capable of bystander killing, allows T-DXd to deliver sufficient cytotoxic effect even when HER2 expression is low, which underpins its activity in HER2-low breast cancer.
Option B: Option B is incorrect because T-DXd, not T-DM1, has the higher ratio, and T-DXd is the agent active in HER2-low disease.
Option C: Option C is incorrect because the two have different ratios (about 3.5 versus about 8) and different HER2-low activity.
Option D: Option D is incorrect because the drug-to-antibody ratio, together with payload permeability, is directly relevant to potency in low-expressing tumors.
Option E: Option E is incorrect because T-DXd has the higher, not lower, ratio, and its design specifically extends activity into HER2-low disease.
15. Pre-medication regimens for monoclonal antibody infusions are tailored to the dominant reaction mechanism of each agent. Which statement correctly discriminates the basis for cetuximab pre-medication from that for the typical cytokine-release-type infusion reaction seen with agents such as rituximab or daratumumab?
A) Cetuximab reactions are cytokine-release reactions, whereas rituximab and daratumumab reactions are immunoglobulin E-mediated, so cetuximab needs no antihistamine
B) Cetuximab pre-medication is unnecessary because its reactions are trivial, whereas only daratumumab requires any pre-medication
C) All three agents cause identical immunoglobulin E-mediated anaphylaxis and require identical epinephrine pre-medication
D) Cetuximab pre-medication targets a true immunoglobulin E-mediated hypersensitivity risk from pre-existing antibodies against the galactose-alpha-1,3-galactose epitope, emphasizing antihistamine coverage, whereas rituximab and daratumumab reactions are predominantly cytokine-release reactions prevented with corticosteroid, antihistamine, and acetaminophen (with a leukotriene modifier added for daratumumab)
E) Rituximab and daratumumab require no pre-medication because cytokine-release reactions cannot be prevented
ANSWER: D
Rationale:
Cetuximab carries a true immunoglobulin E-mediated hypersensitivity risk from pre-existing antibodies against the galactose-alpha-1,3-galactose epitope, so its pre-medication emphasizes antihistamine coverage. In contrast, the infusion reactions of rituximab and daratumumab are predominantly cytokine-release reactions, prevented with corticosteroid, antihistamine, and acetaminophen, with a leukotriene modifier added for daratumumab.
Option A: Option A is incorrect because it reverses the mechanisms; cetuximab is the agent with the immunoglobulin E-mediated risk.
Option B: Option B is incorrect because cetuximab reactions are not trivial and pre-medication is used.
Option C: Option C is incorrect because the agents do not all cause identical immunoglobulin E-mediated anaphylaxis, and routine epinephrine pre-medication is not the standard.
Option E: Option E is incorrect because cytokine-release reactions are mitigated by pre-medication and slowed infusion, so rituximab and daratumumab do receive pre-medication.
16. A clinician is selecting candidates for bevacizumab-containing regimens and must apply its histology-based contraindication. Which statement correctly discriminates the contraindicated setting from an appropriate one and identifies the underlying risk?
A) Bevacizumab is contraindicated in non-squamous non-small cell lung cancer because of catastrophic hemoptysis, but is appropriate in squamous histology
B) Bevacizumab is contraindicated in metastatic colorectal cancer because of bowel perforation risk and may only be used in squamous lung cancer
C) Bevacizumab is safe in all lung histologies because anti-VEGF therapy does not affect tumor vasculature
D) Bevacizumab is contraindicated in any patient with hypertension, which is the principal histology-independent contraindication
E) Bevacizumab is contraindicated in squamous cell non-small cell lung cancer because of the risk of catastrophic pulmonary hemorrhage from tumor cavitation, whereas it is appropriate, with chemotherapy, in non-squamous non-small cell lung cancer and in metastatic colorectal cancer
ANSWER: E
Rationale:
Bevacizumab is contraindicated in squamous cell non-small cell lung cancer because of the risk of catastrophic pulmonary hemorrhage from tumor cavitation; the relevant pivotal trial excluded squamous histology for this reason. It is appropriate, combined with chemotherapy, in non-squamous non-small cell lung cancer and in metastatic colorectal cancer.
Option A: Option A is incorrect because it reverses the histologies; squamous, not non-squamous, is the contraindicated setting.
Option B: Option B is incorrect because bevacizumab is used in metastatic colorectal cancer (with monitoring for perforation) and is contraindicated in squamous, not permitted in it.
Option C: Option C is incorrect because anti-VEGF therapy clearly affects tumor and normal vasculature and is not safe in all histologies.
Option D: Option D is incorrect because hypertension is a manageable toxicity, not the principal histology-independent contraindication; the squamous-histology hemorrhage risk is the key contraindication here.
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