Chapter 33 — Anti-Cancer Drugs Part I: Pharmacology — Module 6 — Miscellaneous Cytotoxics, Drug Interactions, and Supportive Pharmacology
1. Hydroxyurea is used in some protocols as a radiosensitizer, given on a schedule timed to its short plasma half-life. Integrating its mechanism of action with its cell-cycle effects, why does intermittent hydroxyurea enhance the effect of radiation?
A) By inhibiting ribonucleotide reductase it directly breaks double-stranded DNA, adding to the breaks caused by radiation
B) By prolonging its own half-life it maintains continuous suppression of all cell-cycle phases simultaneously
C) By blocking ribonucleotide reductase it stalls cells at the G1/S boundary and depletes the deoxyribonucleotide pool needed to repair radiation-induced DNA damage, synchronizing cells into a radiosensitive state
D) By raising fetal hemoglobin it improves tumor oxygenation and thereby increases radiation sensitivity
E) By inducing CYP3A4 it accelerates clearance of radioprotective metabolites
ANSWER: C
Rationale:
Hydroxyurea inhibits ribonucleotide reductase, which both halts cells attempting DNA synthesis at the G1/S boundary and depletes the deoxyribonucleotide precursor pool. Because radiation kills most effectively when cells cannot repair its DNA damage, a cell population synchronized at the radiosensitive G1/S boundary and simultaneously deprived of the deoxyribonucleotides required for repair is rendered more vulnerable to radiation; the short half-life allows intermittent dosing that synchronizes rather than continuously suppresses.
Option A: Option A is incorrect because hydroxyurea does not itself cleave double-stranded DNA; it blocks precursor synthesis.
Option B: Option B is incorrect because hydroxyurea has a short half-life and acts as an S-phase-specific agent rather than continuously suppressing every phase.
Option D: Option D is incorrect because the fetal hemoglobin effect pertains to sickle cell disease and does not explain radiosensitization through tumor oxygenation.
Option E: Option E is incorrect because hydroxyurea is not a CYP3A4 inducer and the radiosensitizing effect is not mediated by accelerated metabolite clearance.
2. A child receiving asparaginase for ALL develops headache, altered consciousness, and a focal seizure, and imaging confirms cerebral venous sinus thrombosis. Integrating asparaginase pharmacology with this presentation, which explanation best accounts for why a drug that also lowers clotting factors can produce a thrombotic event?
A) Asparaginase suppresses hepatic synthesis of both procoagulant factors and natural anticoagulants such as antithrombin III and protein C, and when the anticoagulant proteins fall more than the procoagulants, the balance tips toward thrombosis
B) Asparaginase directly activates platelets, producing thrombosis independent of any protein changes
C) Asparaginase depletes only fibrinogen, which paradoxically increases clot formation
D) Asparaginase causes thrombosis exclusively through hyperglycemia-induced endothelial injury
E) Asparaginase raises antithrombin III levels, which promotes clotting in cerebral veins
ANSWER: A
Rationale:
Asparaginase depletes asparagine but also broadly reduces hepatic protein synthesis, lowering both procoagulant factors (such as fibrinogen) and the natural anticoagulants antithrombin III and protein C. Because both arms of hemostasis are depleted, the net clinical effect depends on which falls further in a given patient; when the natural anticoagulants are disproportionately reduced, the balance shifts toward thrombosis, and cerebral venous sinus thrombosis is a recognized and serious manifestation.
Option B: Option B is incorrect because asparaginase-associated thrombosis is driven by the hemostatic protein imbalance rather than by direct platelet activation.
Option C: Option C is incorrect because fibrinogen depletion would, if anything, favor bleeding, and the thrombotic tendency reflects loss of anticoagulant proteins.
Option D: Option D is incorrect because, although asparaginase can cause hyperglycemia, thrombosis is explained by the coagulation protein imbalance rather than by hyperglycemic endothelial injury alone.
Option E: Option E inverts the pharmacology, because asparaginase lowers rather than raises antithrombin III.
3. A patient on pegaspargase has tolerated every infusion without any allergic features, but therapeutic drug monitoring shows trough asparaginase activity below the target threshold. Integrating the concepts of silent inactivation and asparaginase preparations, what is the most appropriate next step?
A) Continue pegaspargase unchanged, since the absence of clinical reactions confirms adequate activity
B) Increase the pegaspargase dose and rely on clinical tolerance as the marker of efficacy
C) Premedicate with corticosteroids and antihistamines and continue the same preparation
D) Recognize this as silent inactivation from neutralizing antibodies and switch to a non-cross-reacting preparation such as Erwinia asparaginase, confirming adequate asparagine depletion thereafter
E) Discontinue all asparaginase permanently, since loss of activity indicates intolerance to the drug class
ANSWER: D
Rationale:
Inadequate asparaginase activity despite full clinical tolerance is the signature of silent inactivation, in which neutralizing antibodies reduce enzyme activity without producing a hypersensitivity reaction; the appropriate response is to recognize the pattern and switch to a non-cross-reacting preparation such as Erwinia asparaginase, then confirm adequate asparagine depletion with continued monitoring.
Option A: Option A is incorrect because clinical tolerance does not guarantee adequate activity, which is precisely why monitoring detected the problem.
Option B: Option B is incorrect because simply raising the dose of an antibody-neutralized preparation while trusting tolerance ignores the mechanism and risks under-treatment.
Option C: Option C is incorrect because premedication addresses hypersensitivity reactions, which are absent here, and does not restore neutralized enzyme activity.
Option E: Option E is incorrect because loss of activity to one preparation does not mandate abandoning the entire class; Erwinia asparaginase is the established alternative.
4. The immunomodulatory drugs exert both a direct anti-myeloma effect and an immunostimulatory effect, and both trace to the same molecular event. Integrating the cereblon mechanism across these two effects, which explanation is correct?
A) The anti-myeloma effect comes from cereblon degradation of Ikaros and Aiolos, while the immunostimulatory effect comes from a separate inhibition of ribonucleotide reductase
B) Cereblon-directed degradation of Ikaros and Aiolos both removes transcription factors that drive myeloma survival and, by degrading the same factors in regulatory T cells, releases suppression of interleukin-2 to stimulate the immune response
C) The anti-myeloma effect is immunologic while the immunostimulatory effect is purely anti-angiogenic, and the two are mechanistically unrelated
D) Both effects arise from increased synthesis of Ikaros and Aiolos rather than their degradation
E) The immunostimulatory effect depends on CYP3A4 activation while the anti-myeloma effect depends on renal clearance
ANSWER: B
Rationale:
Both effects flow from the same cereblon-directed degradation of Ikaros and Aiolos. In myeloma cells, loss of these transcription factors removes drivers of survival programs such as IRF4 and MYC, producing the direct anti-myeloma effect; in regulatory T cells, degradation of the same factors lifts their suppression of interleukin-2 production, producing immunostimulation. A single molecular event therefore accounts for both arms of activity.
Option A: Option A is incorrect because the immunostimulatory effect is not mediated by ribonucleotide reductase inhibition, which is the hydroxyurea mechanism.
Option C: Option C is incorrect because the two effects share the cereblon-substrate mechanism rather than being unrelated, and anti-angiogenesis is an additional property rather than the basis of immunostimulation.
Option D: Option D inverts the mechanism, since the drugs cause degradation, not increased synthesis, of Ikaros and Aiolos.
Option E: Option E is incorrect because neither effect is governed by CYP3A4 activation or renal clearance.
5. A patient with multiple myeloma and chronic kidney disease is about to start lenalidomide combined with dexamethasone. Integrating lenalidomide's elimination pathway with its characteristic toxicity, which two-part management approach is correct?
A) No dose change is needed for renal function, and no thromboprophylaxis is required because dexamethasone protects against clots
B) The dose must be increased in renal impairment because clearance is faster, and aspirin is contraindicated
C) The dose depends on CYP3A4 activity, and thromboprophylaxis is unnecessary at any renal function
D) Renal function is irrelevant to dosing because lenalidomide is hepatically metabolized, but thromboprophylaxis is mandatory
E) Because lenalidomide is predominantly renally excreted, the dose must be reduced for the degree of renal impairment, and because the lenalidomide-dexamethasone combination markedly raises venous thromboembolism risk, thromboprophylaxis is mandatory
ANSWER: E
Rationale:
Lenalidomide is cleared predominantly by the kidney, so its dose must be reduced according to the degree of renal impairment, and the lenalidomide-dexamethasone combination substantially increases venous thromboembolism risk, making thromboprophylaxis mandatory; both elements must be addressed together.
Option A: Option A is incorrect because renal impairment requires dose reduction and dexamethasone increases rather than mitigates the clotting risk.
Option B: Option B inverts both points, since renal impairment calls for a lower dose rather than a higher one, and aspirin is in fact a standard prophylactic option in lower-risk patients.
Option C: Option C is incorrect because lenalidomide clearance is renal rather than CYP3A4-dependent, and thromboprophylaxis is required rather than unnecessary.
Option D: Option D misstates the elimination route as hepatic metabolism; lenalidomide is renally excreted, although the recognition that thromboprophylaxis is mandatory is correct.
6. Two oncology patients each have a CYP3A4-based drug interaction: one on vincristine started on voriconazole, the other on imatinib started on rifampin. Integrating the direction of each interaction with its clinical consequence, which statement correctly contrasts the two?
A) Both interactions raise the chemotherapy drug level, so both require a dose reduction of the chemotherapy agent
B) Both interactions lower the chemotherapy drug level, so both require a dose increase of the chemotherapy agent
C) The voriconazole interaction inhibits CYP3A4 and raises vincristine exposure, risking neurotoxicity and calling for vincristine dose reduction, whereas the rifampin interaction induces CYP3A4 and lowers imatinib exposure, risking treatment failure and calling for an imatinib dose increase or substitution of the inducer
D) The voriconazole interaction induces CYP3A4 and lowers vincristine exposure, whereas the rifampin interaction inhibits CYP3A4 and raises imatinib exposure
E) Neither interaction is clinically significant because both drugs have wide therapeutic indices
ANSWER: C
Rationale:
The two interactions run in opposite directions through the same enzyme. Voriconazole inhibits CYP3A4, slowing vincristine metabolism and raising its exposure, which risks severe neurotoxicity and calls for reducing the vincristine dose or substituting a weaker inhibitor; rifampin induces CYP3A4, accelerating imatinib metabolism and lowering its exposure by roughly 70%, which risks treatment failure and calls for increasing the imatinib dose or substituting a non-inducing agent.
Option A: Option A is incorrect because only the inhibitor raises drug levels; the inducer lowers them.
Option B: Option B is incorrect because only the inducer lowers drug levels; the inhibitor raises them.
Option D: Option D reverses both interactions, mislabeling the inhibitor as an inducer and vice versa.
Option E: Option E is incorrect because both vincristine and imatinib have narrow therapeutic indices and these interactions are clinically significant.
7. A patient receiving paclitaxel is also taking gemfibrozil for hypertriglyceridemia, and separately a breast cancer patient on tamoxifen is taking paroxetine. Integrating the responsible cytochrome isoform with each interaction, which mapping is correct?
A) Paclitaxel is metabolized by CYP2C8, which gemfibrozil inhibits to raise paclitaxel exposure; tamoxifen is activated by CYP2D6, which paroxetine inhibits to lower active endoxifen
B) Both drugs are affected through CYP3A4, with gemfibrozil and paroxetine acting as inducers
C) Paclitaxel is activated by CYP2D6 and tamoxifen is metabolized by CYP2C8, so the interacting drugs should be swapped between patients
D) Gemfibrozil lowers paclitaxel exposure by inducing CYP2C8, while paroxetine raises endoxifen by inhibiting CYP2D6
E) Neither interaction matters because gemfibrozil and paroxetine are eliminated renally
ANSWER: A
Rationale:
The two interactions involve different isoforms that must be matched to the correct substrate. Paclitaxel is metabolized primarily by CYP2C8, and the fibrate gemfibrozil inhibits CYP2C8 to increase paclitaxel exposure roughly two-fold; tamoxifen is a prodrug activated by CYP2D6 to endoxifen, and paroxetine inhibits CYP2D6 to reduce endoxifen formation and potentially compromise efficacy.
Option B: Option B is incorrect because the relevant isoforms are CYP2C8 and CYP2D6 respectively, not a shared CYP3A4 pathway, and both interacting drugs act as inhibitors rather than inducers.
Option C: Option C is incorrect because it swaps the substrate-isoform assignments, incorrectly pairing paclitaxel with CYP2D6 and tamoxifen with CYP2C8.
Option D: Option D reverses both directions, since gemfibrozil inhibits rather than induces CYP2C8 and paroxetine lowers rather than raises endoxifen.
Option E: Option E is incorrect because both interactions are clinically meaningful and operate through hepatic metabolism rather than being nullified by renal elimination.
8. A patient on oxaliplatin reports two different sensory problems: tingling triggered by cold drinks in the days after each infusion, and a slowly worsening numbness in the feet building over several cycles. Integrating the two oxaliplatin neuropathy syndromes with management, which approach is correct?
A) Both problems are the same cumulative neuropathy, so both require immediate discontinuation of oxaliplatin
B) Both problems are the acute cold syndrome, so cold-avoidance counseling alone fully addresses each
C) The cold-triggered tingling reflects cumulative dorsal root ganglion injury and warrants dose reduction, while the progressive numbness is harmless and needs no action
D) The cold-triggered tingling is the acute, sodium-channel-mediated syndrome managed by cold-avoidance counseling before each infusion, while the progressive numbness is the cumulative dorsal root ganglion neuropathy that is tracked and may prompt dose modification as it worsens
E) Both problems indicate an allergic reaction to oxaliplatin requiring premedication
ANSWER: D
Rationale:
Oxaliplatin produces two distinct syndromes that call for different responses. The cold-triggered tingling soon after infusion is the acute, sodium-channel-mediated syndrome, addressed by counseling the patient to avoid cold exposure around each infusion; the slowly progressive numbness over multiple cycles is the cumulative dorsal root ganglion neuropathy, which is monitored over time and may prompt dose modification as severity increases.
Option A: Option A is incorrect because the two problems are different syndromes, and the acute cold sensitivity does not by itself mandate discontinuation.
Option B: Option B is incorrect because only the acute syndrome is addressed by cold avoidance; the cumulative neuropathy requires monitoring and possible dose change.
Option C: Option C reverses the mechanisms, misattributing the cold-triggered tingling to cumulative dorsal root ganglion injury and dismissing the progressive numbness that actually warrants attention.
Option E: Option E is incorrect because neither syndrome is an allergic reaction; both are neurotoxic phenomena.
9. Cell-cycle specificity determines not only which tumors respond but also how an agent is best scheduled. Integrating the pharmacology of S-phase-specific agents with dosing strategy, why are fluorouracil and capecitabine often given by continuous infusion or prolonged oral dosing rather than a single bolus?
A) Because they are phase-nonspecific, their effect depends only on the single peak concentration achieved
B) Because they are S-phase-specific and their activity is duration-dependent, prolonged exposure allows more tumor cells to enter the vulnerable S phase while drug is present
C) Because they are M-phase-specific, a single brief exposure arrests all dividing cells at once
D) Because continuous infusion converts them into alkylating agents that damage DNA in every phase
E) Because prolonged exposure raises fetal hemoglobin, which enhances their cytotoxicity
ANSWER: B
Rationale:
Fluorouracil and capecitabine are S-phase-specific antimetabolites whose cytotoxicity is duration-dependent rather than peak-concentration-dependent. Because only the fraction of cells in S phase at any instant is vulnerable, maintaining drug exposure over time through continuous infusion or prolonged oral dosing allows more cells to cycle into S phase while drug is present, increasing cell kill.
Option A: Option A is incorrect because these agents are phase-specific rather than phase-nonspecific, and their effect depends on duration of exposure rather than a single peak.
Option C: Option C describes the behavior of M-phase-specific agents such as vinca alkaloids and taxanes, not the antimetabolites.
Option D: Option D is incorrect because the route of administration does not transform an antimetabolite into an alkylating agent.
Option E: Option E is incorrect because the fetal hemoglobin effect belongs to hydroxyurea in sickle cell disease and does not govern antimetabolite scheduling.
10. Each cytotoxic class carries a signature dose-limiting toxicity that dictates a specific surveillance strategy. Integrating toxicity pattern with the correct monitoring modality, which set of pairings is correct?
A) Anthracyclines require pulmonary function (DLCO) monitoring; bleomycin requires echocardiography; cisplatin requires audiometry only
E) Anthracyclines require echocardiographic monitoring for cumulative cardiomyopathy; bleomycin requires DLCO monitoring for pulmonary fibrosis; platinum compounds require creatinine and neurologic monitoring for nephrotoxicity and neuropathy
ANSWER: E
Rationale:
The signature toxicity of each class maps to a specific surveillance test. Anthracyclines cause cumulative cardiomyopathy, monitored echocardiographically with cumulative dose tracking; bleomycin causes pulmonary fibrosis, monitored by the diffusing capacity for carbon monoxide; and platinum compounds cause nephrotoxicity and cumulative sensory neuropathy, monitored by creatinine and neurologic assessment.
Option A: Option A swaps anthracycline and bleomycin monitoring and reduces cisplatin surveillance to audiometry alone.
Option B: Option B misassigns echocardiography to bleomycin, creatinine to anthracyclines, and DLCO to vinca alkaloids.
Option C: Option C misassigns echocardiography to cisplatin, renal monitoring to bleomycin, and pulmonary monitoring to anthracyclines.
Option D: Option D misassigns cardiac monitoring to vinca alkaloids, audiometry to anthracyclines, and renal monitoring to bleomycin.
11. Two cancer survivors develop treatment-related myeloid neoplasms: one five years after high-dose cyclophosphamide conditioning, the other two years after an etoposide-containing regimen. Integrating latency, cytogenetics, and prognosis, which comparison is correct?
A) The cyclophosphamide-related case has a long latency with a preceding myelodysplastic phase, unbalanced loss of chromosome 5 or 7 material, and a poor prognosis, whereas the etoposide-related case has a short latency, de novo acute leukemia with a balanced KMT2A rearrangement, and an intermediate prognosis
B) Both cases have identical short latency and balanced translocations, differing only in the chemotherapy that caused them
C) The cyclophosphamide-related case has a short latency with KMT2A rearrangement, while the etoposide-related case has a long latency with monosomy 7
D) Both cases carry a favorable prognosis and resolve with observation alone
E) The etoposide-related case is preceded by a long myelodysplastic phase, while the cyclophosphamide-related case appears de novo within months
ANSWER: A
Rationale:
The two entities differ systematically by causative class. Alkylating agent-related disease, as from cyclophosphamide, has a long latency of roughly 5 to 10 years, is typically preceded by a myelodysplastic phase, carries unbalanced losses of chromosome 5 or 7 material, and has a poor prognosis; topoisomerase II inhibitor-related disease, as from etoposide, has a short latency of about 1 to 3 years, presents as de novo acute myeloid leukemia with a balanced KMT2A rearrangement at 11q23, and carries an intermediate prognosis.
Option B: Option B is incorrect because the two differ in latency and cytogenetics rather than being identical.
Option C: Option C reverses the two phenotypes, assigning the KMT2A short-latency pattern to cyclophosphamide and the monosomy-7 long-latency pattern to etoposide.
Option D: Option D is incorrect because neither entity carries a favorable prognosis or resolves with observation.
Option E: Option E reverses the latency and prodrome, since the myelodysplastic phase precedes the alkylating agent type and the de novo presentation characterizes the topoisomerase II inhibitor type.
12. A woman in her second trimester is diagnosed with diffuse large B-cell lymphoma. Integrating the trimester-based principles of chemotherapy in pregnancy with the class-specific exception for antimetabolites, which statement is correct?
A) All chemotherapy is equally contraindicated throughout pregnancy, so treatment must be deferred until after delivery regardless of timing
B) Because organogenesis is complete, any agent including methotrexate may now be used freely with no class-specific concern
C) Many regimens such as R-CHOP can be given in the second trimester with acceptable outcomes now that organogenesis is complete, but antimetabolites such as methotrexate remain relatively contraindicated throughout pregnancy, and chemotherapy should be stopped several weeks before delivery
D) Only oral agents are safe in the second trimester because they do not cross the placenta
E) Antimetabolites are the preferred agents in pregnancy because their anti-folate action spares the fetus
ANSWER: C
Rationale:
After the first trimester, organogenesis is complete and the risk of structural teratogenicity falls, so many regimens including R-CHOP for diffuse large B-cell lymphoma can be administered in the second and third trimesters with acceptable outcomes; however, antimetabolites such as methotrexate remain relatively contraindicated throughout pregnancy because of their anti-folate mechanism and ongoing fetal requirements, and chemotherapy should be stopped several weeks before anticipated delivery to allow drug clearance and reduce neonatal marrow suppression.
Option A: Option A is incorrect because risk is concentrated in the first trimester rather than being uniform, and treatment need not be deferred entirely in the second trimester.
Option B: Option B is incorrect because the completion of organogenesis does not lift the specific contraindication to antimetabolites like methotrexate.
Option D: Option D is incorrect because route of administration does not determine placental transfer; many agents cross regardless of route.
Option E: Option E inverts the safety profile, since the anti-folate mechanism makes antimetabolites hazardous rather than fetus-sparing.
13. Rational dose adjustment for organ impairment requires matching each drug to its primary elimination pathway. Integrating elimination route with the appropriate dose decision, which statement is correct?
A) Doxorubicin is renally cleared, so its dose is reduced based on creatinine clearance, while carboplatin is hepatically cleared and reduced based on bilirubin
B) Carboplatin is renally cleared and dosed to a target exposure using renal function, while doxorubicin is hepatically eliminated and reduced according to bilirubin in hepatic impairment
C) Both carboplatin and doxorubicin are renally cleared, so both are dosed using creatinine clearance alone
D) Both carboplatin and doxorubicin are hepatically eliminated, so both require bilirubin-based reduction
E) Neither drug requires dose adjustment for organ impairment because both are metabolized to inactive products independent of organ function
ANSWER: B
Rationale:
Correct dosing follows each drug's elimination route. Carboplatin is renally cleared and is dosed to a target exposure based on renal function, whereas doxorubicin is eliminated hepatically and is dose-reduced according to bilirubin in hepatic impairment.
Option A: Option A reverses both assignments, incorrectly making doxorubicin renally cleared and carboplatin hepatically cleared.
Option C: Option C is incorrect because doxorubicin is hepatically rather than renally eliminated, so creatinine-based dosing does not apply to it.
Option D: Option D is incorrect because carboplatin is renally cleared rather than hepatically eliminated, so bilirubin-based reduction does not apply to it.
Option E: Option E is incorrect because both drugs require organ-function-based dose adjustment rather than being independent of organ function.
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