Chapter 33 — Anti-Cancer Drugs Part I: Pharmacology — Module 4 — Topoisomerase Inhibitors and Antitumor Antibiotics
1. A 38-year-old man with good-risk metastatic testicular germ cell tumor is being planned for curative-intent chemotherapy. His pretreatment pulmonary function testing shows a reduced diffusing capacity for carbon monoxide (DLCO), and he has a history of moderate emphysema. The standard option is three cycles of BEP (bleomycin, etoposide, cisplatin). Which modification best addresses his specific risk while preserving curative intent?
A) Proceed with BEP unchanged, because pulmonary risk factors do not alter regimen choice in germ cell tumor
B) Substitute four cycles of EP (etoposide, cisplatin), omitting bleomycin to avoid added pulmonary toxicity while maintaining comparable cure rates in good-risk disease
C) Replace cisplatin with carboplatin to reduce lung injury
D) Add prophylactic dexrazoxane to protect the lungs from bleomycin
E) Give BEP but double the bleomycin dose to shorten the number of cycles needed
ANSWER: B
Rationale:
This patient's reduced DLCO and emphysema mark him as high risk for bleomycin pulmonary toxicity, so the rational modification is to omit bleomycin and use four cycles of EP, which achieves comparable cure rates to three cycles of BEP in good-risk germ cell tumor while removing the bleomycin pulmonary hazard. This integrates the toxicity-risk profile with regimen design rather than applying a one-size protocol.
Option A: Option A is incorrect because pulmonary risk factors absolutely do influence whether bleomycin should be included; ignoring a reduced DLCO would expose him to avoidable lung injury.
Option C: Option C is incorrect because substituting carboplatin for cisplatin addresses platinum-related toxicities (renal, otologic, emetic), not bleomycin lung toxicity, and carboplatin substitution can compromise cure in germ cell tumor.
Option D: Option D is incorrect because dexrazoxane protects against anthracycline cardiotoxicity and has no established role in preventing bleomycin pulmonary toxicity.
Option E: Option E is incorrect because increasing the bleomycin dose would raise, not lower, pulmonary toxicity risk, directly worsening his vulnerability.
2. A 60-year-old woman with metastatic colorectal cancer is to begin FOLFIRI (folinic acid, fluorouracil, irinotecan). Pre-treatment genotyping returns UGT1A1*28/*28 (homozygous for the reduced-activity promoter variant of the enzyme that inactivates SN-38, the active irinotecan metabolite). How should this result guide the first cycle, and why?
A) No change is needed because the variant affects only the early cholinergic diarrhea, not systemic toxicity
B) Increase the irinotecan dose because the variant accelerates SN-38 clearance
C) Switch irinotecan to topotecan, since UGT1A1 status predicts topotecan toxicity identically
D) Consider a reduced irinotecan starting dose, because impaired glucuronidation lets SN-38 accumulate, raising the risk of severe neutropenia and diarrhea
E) Proceed at full dose but omit folinic acid to offset the genetic risk
ANSWER: D
Rationale:
Homozygous UGT1A1*28 substantially lowers the glucuronidation capacity that inactivates SN-38, so the active metabolite accumulates to higher and more prolonged levels, increasing the risk of severe neutropenia and grade 3 to 4 diarrhea at standard doses; the appropriate response is to consider a reduced irinotecan starting dose with close monitoring.
Option A: Option A is incorrect because the variant affects systemic SN-38 exposure and therefore marrow and gut toxicity, not merely the early cholinergic syndrome.
Option B: Option B is incorrect because the variant reduces, not accelerates, SN-38 clearance, so increasing the dose would compound toxicity.
Option C: Option C is incorrect because topotecan toxicity is not governed by UGT1A1 (topotecan is renally cleared and is not a prodrug requiring this pathway), so the genotype does not transfer to topotecan dosing.
Option E: Option E is incorrect because folinic acid modulates fluorouracil activity and does not offset irinotecan-related genetic toxicity risk; omitting it would not address SN-38 accumulation.
3. A 24-year-old patient cured of one malignancy now faces a treatment decision in which two regimens have similar efficacy: one built on a topoisomerase II poison (such as etoposide) and one built on a topoisomerase I inhibitor (such as topotecan). The patient is highly concerned about the long-term risk of a treatment-caused second blood cancer. Based on mechanism, which statement best informs this decision?
A) The topoisomerase I-based regimen carries less risk of treatment-related acute myeloid leukemia, because the secondary-leukemia signature (often MLL rearrangement at 11q23) is linked to topoisomerase II poisons rather than topoisomerase I inhibitors
B) The topoisomerase I-based regimen carries the higher leukemia risk, because single-strand breaks are more mutagenic than double-strand breaks
C) Both regimens carry identical secondary-leukemia risk, because all DNA-damaging drugs cause AML at the same rate
D) Neither regimen carries any secondary-leukemia risk, so the concern is unfounded
E) The topoisomerase II-based regimen is safer because its double-strand breaks are always repaired perfectly
ANSWER: A
Rationale:
Treatment-related AML with the characteristic MLL/11q23 rearrangement and short latency is specifically associated with topoisomerase II poisons such as etoposide; topoisomerase I inhibitors do not carry this same recognized secondary-leukemia signature. For a young patient prioritizing low long-term leukemia risk, the topoisomerase I-based regimen is mechanistically the lower-risk choice when efficacy is comparable.
Option B: Option B is incorrect because it inverts the risk; the leukemia association lies with the topoisomerase II poisons, not the topoisomerase I inhibitors.
Option C: Option C is incorrect because DNA-damaging drugs do not all cause AML at equal rates; the risk is mechanism- and class-specific.
Option D: Option D is incorrect because topoisomerase II poisons do carry a real, quantifiable secondary-AML risk, so the concern is legitimate.
Option E: Option E is incorrect because double-strand breaks from topoisomerase II poisoning are precisely what can be misrepaired into leukemogenic translocations, so they are not always repaired perfectly.
4. A patient treated years ago for breast cancer received a substantial cumulative dose of epirubicin. She now needs anthracycline-based therapy for a new malignancy, and the oncologist is considering doxorubicin. To estimate her cumulative cardiac risk before prescribing, which approach is correct?
A) Count only the planned doxorubicin dose, since the prior epirubicin has cleared the body
B) Disregard prior anthracycline exposure because epirubicin and doxorubicin act on different targets
C) Use the raw milligram totals of each drug added together without any adjustment
D) Assume the heart fully recovers between courses, so each course can be assessed in isolation
E) Convert the prior epirubicin and the planned doxorubicin into doxorubicin-equivalent doses and sum them, because anthracycline cardiotoxicity is cumulative and irreversible across all lifetime exposure
ANSWER: E
Rationale:
Because anthracycline cardiotoxicity reflects cumulative, irreversible cardiomyocyte injury, the correct method is to express all prior and planned anthracycline exposure in common doxorubicin-equivalent units (epirubicin is less cardiotoxic per milligram, so a conversion factor applies) and sum them to gauge how much of the safe lifetime ceiling remains.
Option A: Option A is incorrect because plasma clearance of the prior drug does not erase the accumulated cardiac injury; prior exposure still counts.
Option B: Option B is incorrect because epirubicin and doxorubicin are both anthracyclines acting on topoisomerase II with shared cardiotoxic mechanisms, so prior exposure is directly relevant.
Option C: Option C is incorrect because raw milligram totals ignore the differing per-milligram cardiotoxicity of the two agents; conversion to equivalents is required.
Option D: Option D is incorrect because the heart does not fully recover between anthracycline courses; the injury is cumulative, which is the whole basis for lifetime dose tracking.
5. A 29-year-old man who completed bleomycin-containing chemotherapy eight months ago now requires emergency general anesthesia for an appendectomy. The surgical team asks how the bleomycin history should change perioperative management. What is the most appropriate guidance?
A) The bleomycin risk expired after six months, so standard high inspired oxygen is now safe
B) Bleomycin prolongs neuromuscular blockade, so paralytic doses should be halved, but oxygen settings are unrestricted
C) Keep the inspired oxygen fraction as low as is consistent with adequate oxygen saturation throughout and after anesthesia, because bleomycin-sensitized lung can develop severe injury with high oxygen exposure, and no firmly established safe interval exists
D) Avoid all volatile anesthetic agents, as they react chemically with residual bleomycin
E) Pretreat with high-dose corticosteroids, which fully eliminate the oxygen-related pulmonary risk
ANSWER: C
Rationale:
The bleomycin-oxygen interaction means that high inspired oxygen can trigger severe, potentially fatal lung injury in previously exposed patients, and there is no firmly established safe interval after which the risk disappears; the correct management is to titrate the inspired oxygen fraction to the lowest level consistent with adequate saturation during and after anesthesia and to alert the anesthesia team.
Option A: Option A is incorrect because the risk does not reliably expire at six months; an eight-month interval does not license unrestricted high oxygen.
Option B: Option B is incorrect because bleomycin does not prolong neuromuscular blockade, and the oxygen fraction is precisely what must be restricted, not left unrestricted.
Option D: Option D is incorrect because the hazard is high inspired oxygen, not a chemical reaction with volatile anesthetics, so banning volatiles does not address the actual risk.
Option E: Option E is incorrect because corticosteroids do not eliminate the oxygen-related pulmonary risk; oxygen titration remains essential.
6. A patient receiving irinotecan develops cramping, watery eyes, sweating, and diarrhea about 30 minutes into the infusion. These symptoms resolve with treatment. Three days later, at home, the patient develops a separate episode of profuse watery diarrhea. Which pairing of treatments correctly matches each episode?
A) Both episodes are treated with high-dose loperamide, since timing does not change management
B) The infusion-time episode is treated with atropine (early cholinergic syndrome from acetylcholinesterase inhibition); the day-three episode is treated with high-dose loperamide (late mucosal injury from luminal SN-38)
C) The infusion-time episode is treated with loperamide; the day-three episode is treated with atropine
D) Both episodes are treated with atropine, since both are cholinergic
E) The day-three episode requires immediate atropine because all delayed diarrhea is cholinergic
ANSWER: B
Rationale:
The two irinotecan diarrhea syndromes are distinguished by timing and mechanism: the infusion-time episode with cholinergic features (lacrimation, diaphoresis, cramping) reflects acetylcholinesterase inhibition and is treated with atropine, whereas the delayed episode arises from luminal SN-38 mucosal toxicity and is treated with high-dose loperamide. Correctly applying the timing-mechanism distinction selects the right drug for each.
Option A: Option A is incorrect because timing fundamentally changes management; loperamide does not treat the early cholinergic syndrome.
Option C: Option C is incorrect because it reverses the correct assignments, giving the early cholinergic episode the late-diarrhea treatment and vice versa.
Option D: Option D is incorrect because the late episode is mucosal, not cholinergic, so atropine is inappropriate for it.
Option E: Option E is incorrect because delayed diarrhea is the mucosal SN-38 syndrome treated with loperamide, not a cholinergic process treated with atropine.
7. An elderly, frail patient with small cell lung cancer cannot tolerate an intensive intravenous cisplatin-based combination. The oncologist elects prolonged oral etoposide over several days rather than a single large intravenous bolus of the same total dose. What is the pharmacological rationale?
A) Oral etoposide is fully absorbed, so it always delivers a higher dose than the intravenous route
B) A single large bolus maximizes the peak concentration, which is what drives etoposide efficacy
C) Prolonged dosing converts etoposide into a topoisomerase I inhibitor, broadening its activity
D) Etoposide is schedule-dependent: spreading the same total dose over several days sustains exposure during the cell-cycle window when topoisomerase II is vulnerable, improving response compared with bolus dosing
E) Oral dosing eliminates the risk of secondary leukemia associated with etoposide
ANSWER: D
Rationale:
Etoposide exhibits schedule dependency: dividing the same total dose into prolonged lower-dose exposure sustains drug levels across more of the cell-cycle window in which topoisomerase II is active, producing higher response rates than an equivalent single bolus. This makes prolonged oral dosing a rational choice for a frail patient who cannot tolerate intensive intravenous combinations.
Option A: Option A is incorrect because oral etoposide bioavailability is incomplete and variable (roughly 50%), so it does not deliver a higher dose than the intravenous route.
Option B: Option B is incorrect because etoposide efficacy is not peak-concentration driven; sustained exposure, not a high peak, improves response.
Option C: Option C is incorrect because etoposide remains a topoisomerase II poison regardless of schedule; dosing does not change its molecular target.
Option E: Option E is incorrect because the secondary-leukemia risk relates to etoposide exposure itself and is not eliminated by choosing the oral route.
8. A patient with recurrent ovarian cancer has previously received conventional doxorubicin and is approaching the cumulative dose associated with significant cardiac risk, but still benefits from anthracycline therapy. The oncologist selects pegylated liposomal doxorubicin. What is the expected tradeoff of this choice?
A) Reduced cardiotoxicity and myelosuppression relative to conventional doxorubicin, but a new dose-limiting toxicity of hand-foot syndrome (palmar-plantar erythrodysesthesia)
B) Increased cardiotoxicity but elimination of all skin toxicity
C) Conversion of the drug to a non-anthracycline mechanism, removing the cumulative-dose concern entirely
D) A markedly shorter circulation time requiring continuous infusion
E) Loss of antitumor activity in ovarian cancer, making it an inappropriate choice
ANSWER: A
Rationale:
Pegylated liposomal doxorubicin shifts the toxicity profile: prolonged circulation and tumor accumulation via the enhanced permeability and retention effect reduce cardiotoxicity, myelosuppression, and alopecia, while hand-foot syndrome (and mucositis) becomes the new dose-limiting toxicity. For a patient near the conventional doxorubicin cardiac ceiling who still benefits from anthracycline therapy, this is a rational tradeoff.
Option B: Option B is incorrect because liposomal encapsulation reduces cardiotoxicity and introduces skin toxicity (hand-foot syndrome), the opposite of the claim.
Option C: Option C is incorrect because the drug remains a topoisomerase II-active anthracycline; the cumulative-dose principle still applies, even if the threshold is more favorable.
Option D: Option D is incorrect because pegylated liposomal doxorubicin has a markedly prolonged, not shortened, circulation time.
Option E: Option E is incorrect because liposomal doxorubicin is an approved and active agent in ovarian cancer, so it is an appropriate choice.
9. A patient with HER2-positive breast cancer (a tumor overexpressing the human epidermal growth factor receptor 2) is to receive both an anthracycline and trastuzumab (a monoclonal antibody targeting HER2). Guidelines direct that these be given sequentially rather than concurrently. What is the pharmacological basis for this rule?
A) Trastuzumab inactivates doxorubicin chemically when mixed in the same infusion
B) Concurrent administration reduces the antitumor efficacy of both drugs
C) Trastuzumab and anthracyclines have additive cardiotoxicity, so concurrent use markedly increases the risk of heart failure; separating them in time reduces that combined cardiac insult
D) Trastuzumab accelerates anthracycline clearance, requiring higher anthracycline doses if given together
E) The two drugs compete for the same topoisomerase II target, cancelling each other's effect
ANSWER: C
Rationale:
Trastuzumab and anthracyclines each stress the myocardium, and their cardiotoxic effects are additive; giving them concurrently markedly raises the incidence of clinical heart failure, which is why they are administered sequentially to limit the combined cardiac insult while preserving the benefit of each.
Option A: Option A is incorrect because the concern is biological additive cardiotoxicity in the patient, not chemical inactivation of doxorubicin by trastuzumab in the infusion.
Option B: Option B is incorrect because the rationale for sequencing is cardiac safety, not loss of antitumor efficacy.
Option D: Option D is incorrect because trastuzumab does not accelerate anthracycline clearance, and the sequencing rule is not a pharmacokinetic dosing adjustment.
Option E: Option E is incorrect because trastuzumab targets the HER2 receptor, not topoisomerase II, so the two do not compete for the same target.
10. A patient midway through BEP chemotherapy reports a new dry cough and exertional dyspnea. Serial pulmonary function testing shows the diffusing capacity for carbon monoxide (DLCO) has fallen substantially from baseline, and a chest CT shows bilateral basal ground-glass opacities. What does this constellation most likely represent, and what is the immediate implication?
A) Cisplatin nephrotoxicity, requiring intravenous hydration
B) Etoposide-induced secondary leukemia, requiring bone marrow biopsy
C) An expected, benign finding requiring no change in therapy
D) Doxorubicin cardiomyopathy, requiring echocardiography and dexrazoxane
E) Early bleomycin pulmonary toxicity, which should prompt consideration of bleomycin discontinuation and pulmonary evaluation, since DLCO decline precedes overt symptoms
ANSWER: E
Rationale:
A falling DLCO with new nonproductive cough, exertional dyspnea, and basal ground-glass opacities in a patient receiving bleomycin is the classic early picture of bleomycin pulmonary toxicity; because DLCO decline precedes overt symptoms, this should prompt consideration of stopping bleomycin and pursuing pulmonary evaluation.
Option A: Option A is incorrect because the findings are pulmonary and DLCO-based, not renal; cisplatin nephrotoxicity would present with rising creatinine, not falling DLCO.
Option B: Option B is incorrect because the picture is one of interstitial lung injury, not leukemia; a marrow biopsy does not address declining DLCO.
Option C: Option C is incorrect because a substantial DLCO decline with symptoms and imaging changes is not benign and demands action.
Option D: Option D is incorrect because doxorubicin (not part of standard BEP) causes cardiomyopathy detected by echocardiography, not the DLCO and ground-glass changes described, which point to the lungs and bleomycin.
11. A patient with metastatic disease is responding well to doxorubicin but is approaching the cumulative dose at which cardiac risk rises sharply. Rather than stopping the effective drug outright, the oncologist adds dexrazoxane. Which statement best integrates the mechanism and the clinical reasoning behind this decision?
A) Dexrazoxane is added because it increases doxorubicin's antitumor potency, allowing fewer cycles
B) Dexrazoxane chelates intracellular iron, reducing the iron-dependent reactive oxygen species that injure cardiomyocytes, which can allow continued anthracycline therapy with lower added cardiac risk in a responding patient near the dose ceiling
C) Dexrazoxane regenerates cardiomyocytes already lost, reversing prior cardiac damage
D) Dexrazoxane works by speeding renal clearance of doxorubicin, lowering systemic exposure
E) Dexrazoxane should be used routinely from the first dose in every patient because it has no downsides
ANSWER: B
Rationale:
Dexrazoxane enters cardiomyocytes and, in its active iron-chelating form, binds intracellular free iron and reduces the iron-dependent reactive oxygen species that drive anthracycline cardiac injury; adding it for a responding patient who is approaching the cumulative ceiling can lower the added cardiac risk of continued anthracycline therapy without sacrificing the drug's benefit.
Option A: Option A is incorrect because dexrazoxane is cardioprotective, not a potency enhancer; it is not added to increase antitumor effect.
Option C: Option C is incorrect because cardiomyocytes are postmitotic and dexrazoxane prevents further injury rather than regenerating already-lost cells.
Option D: Option D is incorrect because dexrazoxane acts intracellularly on iron chemistry, not by accelerating renal clearance of doxorubicin.
Option E: Option E is incorrect because dexrazoxane is not free of downsides (it has mild myelosuppressive effects and pediatric second-malignancy concerns) and its approved use is targeted to patients with substantial prior anthracycline exposure, not routine first-dose use in everyone.
12. A patient cured of a germ cell tumor with a BEP-based regimen develops acute myeloid leukemia two years after treatment. Cytogenetics reveal a balanced rearrangement involving chromosome 11q23 (the MLL gene), and there was no preceding myelodysplastic phase. Which component of the prior regimen is the most likely cause, and what feature confirms the reasoning?
A) Cisplatin, because platinum agents characteristically cause 11q23-rearranged leukemia with short latency
B) Bleomycin, because its pulmonary toxicity extends to leukemogenesis in the marrow
C) Carboplatin, because it is the agent most associated with balanced translocations
D) Etoposide, because topoisomerase II poisons characteristically cause treatment-related AML with 11q23/MLL rearrangement, short latency (1 to 3 years), and no preceding myelodysplastic phase
E) Folinic acid, because its role in nucleotide synthesis drives secondary leukemia
ANSWER: D
Rationale:
The combination of an 11q23/MLL balanced rearrangement, a short latency of roughly two years, and the absence of a preceding myelodysplastic phase is the signature of topoisomerase II poison-related leukemia, and etoposide is the component of BEP responsible for this pattern. Integrating the cytogenetics, latency, and drug exposure points squarely to etoposide.
Option A: Option A is incorrect because platinum agents are more associated with the alkylator-type pattern and are not the classic cause of 11q23-rearranged, short-latency AML.
Option B: Option B is incorrect because bleomycin's toxicity is pulmonary and it is notably marrow-sparing, not leukemogenic in this pattern.
Option C: Option C is incorrect because carboplatin is not part of standard BEP and is not the agent characteristically linked to balanced 11q23 translocations.
Option E: Option E is incorrect because folinic acid is a supportive/rescue agent and is not a cause of treatment-related leukemia.
13. A patient receiving BEP (bleomycin, etoposide, cisplatin) develops, over the course of therapy, a declining DLCO with a dry cough, profound neutropenia, and progressive hearing loss with tinnitus. Correctly attributing each toxicity to its drug, which assignment is correct?
A) Declining DLCO/cough from bleomycin (pulmonary toxicity); neutropenia chiefly from etoposide (myelosuppression); hearing loss/tinnitus from cisplatin (ototoxicity)
B) Declining DLCO/cough from cisplatin; neutropenia from bleomycin; hearing loss from etoposide
C) All three toxicities are caused by etoposide alone
D) Declining DLCO/cough from etoposide; neutropenia from cisplatin; hearing loss from bleomycin
E) Hearing loss from bleomycin; pulmonary toxicity from cisplatin; neutropenia is not expected with this regimen
ANSWER: A
Rationale:
Each toxicity maps to its characteristic agent: the falling DLCO and dry cough reflect bleomycin pulmonary toxicity; the profound neutropenia is chiefly etoposide-driven myelosuppression (the dose-limiting toxicity of etoposide), with cisplatin also contributing to marrow suppression; and the hearing loss with tinnitus is cisplatin ototoxicity. Integrating the toxicity profile of each drug allows correct attribution.
Option B: Option B is incorrect because it swaps the pulmonary toxicity to cisplatin and ototoxicity to etoposide, both wrong; bleomycin is pulmonary and cisplatin is ototoxic.
Option C: Option C is incorrect because the three toxicities arise from different drugs, not from etoposide alone.
Option D: Option D is incorrect because it misassigns pulmonary toxicity to etoposide and ototoxicity to bleomycin, reversing the correct attributions.
Option E: Option E is incorrect because hearing loss is from cisplatin (not bleomycin), pulmonary toxicity is from bleomycin (not cisplatin), and neutropenia is very much expected with this regimen.
This Web-based pharmacology and disease-based integrated teaching site is based on reference materials that are believed reliable and consistent with standards accepted at the time of development.
Possibility of error and on-going research and development in medical sciences do not allow assurance that the information contained herein is in every respect accurate or complete.
Users should confirm the information contained herein with other sources.
This site should only be considered as a teaching aid for undergraduate and graduate biomedical education and is intended only as a teaching site.
Information contained here should not be used for patient management and should not be used as a substitute for consultation with practicing medical professionals.
Users of this website should check the product information sheet included in the package of any drug they plan to administer to be certain that the information contained in this site is accurate and that changes have not been made in the recommended dose or in the contraindications for administration.
Medical or other information thus obtained should not be used as a substitute for consultation with practicing medical or scientific or other professionals.