1. A patient on nilotinib for CML develops nausea, and a colleague proposes adding ondansetron, an antiemetic that can prolong the QT interval. You also learn the patient has been taking each nilotinib dose with breakfast "to settle the stomach." Integrating nilotinib's absorption behavior with its mechanism of cardiac toxicity, which assessment best captures the combined risk and the correct response?
A) The food and the antiemetic both lower nilotinib exposure, so the only concern is loss of leukemia control, not arrhythmia
B) Neither factor matters because nilotinib's QTc effect is fixed and independent of drug concentration
C) Taking nilotinib with food raises its concentration, and because its QTc-prolonging effect is concentration-dependent, the higher level plus a second QTc-prolonging drug compounds the arrhythmia risk; the patient should resume strict fasting and a non-QTc-prolonging antiemetic should be chosen
D) Food has no effect on nilotinib, so only the ondansetron needs to be stopped
E) The combination is safe as long as the nilotinib dose is doubled to overcome the antiemetic interaction
ANSWER: C
Rationale:
Option C is correct. Two effects stack here. First, taking nilotinib with food increases its exposure substantially (a high-fat meal raises the AUC by roughly 80%), and its QTc-prolonging effect is concentration-dependent — so a food-boosted level lengthens the QTc more. Second, adding a separate QTc-prolonging agent such as ondansetron contributes additional QTc effect. The combined result is a meaningfully greater risk of a dangerous ventricular arrhythmia. The correct response integrates both: restore strict fasting (no food 2 hours before and 1 hour after the dose) and select an antiemetic that does not prolong the QTc.
Option A: Option A is incorrect. Food raises rather than lowers nilotinib exposure, so the dominant concern is increased arrhythmia risk, not subtherapeutic dosing.
Option B: Option B is incorrect. Nilotinib's QTc effect is concentration-dependent, so a higher level produces a larger QTc effect; the risk is not fixed.
Option D: Option D is incorrect. Food does affect nilotinib (it increases exposure), so addressing the antiemetic alone is insufficient — the fasting rule must also be restored.
Option E: Option E is incorrect. Doubling the dose would raise the concentration further and worsen the concentration-dependent QTc risk, the opposite of what safety requires.
2. A patient on dasatinib for CML is referred for new reflux symptoms, and the covering clinician starts omeprazole, a proton pump inhibitor (PPI). Two months later the BCR-ABL1 transcript level, which had been falling, has plateaued. Integrating dasatinib's absorption requirement with this new medication, what is the best explanation and corrective action?
A) The PPI raised gastric pH and reduced dasatinib dissolution and absorption, lowering its level enough to stall the molecular response; the PPI should be replaced with a short-acting H2-receptor antagonist administered separated in time from the dasatinib dose (or an antacid likewise time-separated)
B) The plateau reflects emergence of T315I, so therapy should be switched to nilotinib regardless of the PPI
C) The PPI increased dasatinib absorption to toxic levels, so the dasatinib dose should be reduced
D) PPIs have no interaction with dasatinib, so the plateau must be due to nonadherence alone
E) Adding a second PPI would lower gastric pH further and restore dasatinib absorption
ANSWER: A
Rationale:
Option A is correct. Dasatinib requires an acidic gastric environment to dissolve before absorption. A PPI strongly suppresses acid and raises gastric pH, reducing dasatinib dissolution and lowering its exposure (on the order of 40–50%) — enough to blunt the molecular response, which fits the plateau in the transcript level. The integrated fix is to stop the PPI and, if acid suppression is still needed, use a short-acting H2-receptor antagonist dosed separated in time from dasatinib (or a time-separated antacid), so the brief reduction in acidity does not coincide with dasatinib absorption.
Option B: Option B is incorrect. A plateau attributable to a known absorption interaction does not establish a T315I mutation; mutation testing would be appropriate only after the interaction is addressed, and switching blindly to nilotinib both ignores the PPI cause and would be ineffective against T315I in any case.
Option C: Option C is incorrect. A PPI decreases, not increases, dasatinib exposure; the problem is too little drug, so a dose reduction is the wrong direction.
Option D: Option D is incorrect. The PPI interaction is real and clinically significant, so attributing the plateau to nonadherence alone overlooks the pharmacologic cause.
Option E: Option E is incorrect. PPIs raise gastric pH; adding a second one would further impair dasatinib absorption rather than restore it.
3. A patient starting imatinib for CML is already taking warfarin (metabolized by CYP2C9) and simvastatin (metabolized by CYP3A4). Imatinib inhibits both CYP2C9 and CYP3A4. Integrating imatinib's enzyme-inhibitory profile with the metabolism of these two co-medications, what combined effect should you anticipate?
A) Imatinib will induce both enzymes, lowering warfarin and simvastatin levels and reducing the effect of each
B) By inhibiting CYP2C9, imatinib slows warfarin breakdown and raises the INR (bleeding risk), and by inhibiting CYP3A4 it raises simvastatin levels (increasing myopathy and rhabdomyolysis risk); both co-medications require monitoring and likely dose adjustment or substitution
C) Imatinib affects only warfarin, because statins are not metabolized by any enzyme imatinib inhibits
D) Imatinib affects only simvastatin, because warfarin is eliminated unchanged by the kidneys
E) The two interactions cancel out, so no net change in either drug's effect is expected
ANSWER: B
Rationale:
Option B is correct. Imatinib is an inhibitor of both CYP2C9 and CYP3A4, and each co-medication is a substrate of one of those enzymes. Inhibiting CYP2C9 slows warfarin metabolism, raising warfarin levels and the INR, which increases bleeding risk. Inhibiting CYP3A4 raises simvastatin exposure, increasing the risk of statin myopathy and rhabdomyolysis. The integrated management is to monitor closely and adjust: intensify INR monitoring (or switch warfarin to low-molecular-weight heparin) and reduce or substitute the statin (a non-CYP3A4 statin is preferred).
Option A: Option A is incorrect. Imatinib inhibits these enzymes rather than inducing them, so the levels of both substrates rise, not fall.
Option C: Option C is incorrect. Simvastatin is a CYP3A4 substrate, and imatinib inhibits CYP3A4, so the statin is also affected.
Option D: Option D is incorrect. Warfarin is metabolized by CYP2C9 (which imatinib inhibits), not eliminated unchanged by the kidneys, so warfarin is affected.
Option E: Option E is incorrect. The two interactions act on different substrates in the same direction (both substrate levels rise); they do not cancel.
4. A patient on imatinib for CML is diagnosed with active tuberculosis, and the infectious disease team plans a rifampin-based regimen. Rifampin is a strong inducer of CYP3A4, the enzyme that metabolizes imatinib. Integrating this induction effect with the need to maintain leukemia control, what is the most appropriate management?
A) No change is needed, because rifampin does not interact with imatinib
B) Reduce the imatinib dose, because rifampin will raise imatinib levels toward toxicity
C) Stop imatinib entirely for the duration of TB therapy, since the two cannot be co-administered under any circumstances
D) Anticipate a large fall in imatinib exposure (roughly 60–70%) from CYP3A4 induction; either increase the imatinib dose with plasma trough monitoring or, in consultation with the ID team, use a non-inducing alternative to rifampin to preserve leukemia control
E) Switch imatinib to an intravenous formulation, which bypasses the rifampin interaction
ANSWER: D
Rationale:
Option D is correct. Rifampin strongly induces CYP3A4, increasing the enzyme available to metabolize imatinib and lowering imatinib exposure by roughly 60–70% — enough to drop below the threshold needed to sustain the molecular response and risk loss of leukemia control. The integrated solution accounts for both diseases: either raise the imatinib dose (commonly by about 50%) with plasma trough monitoring to confirm adequate exposure, or coordinate with the infectious disease team to use a non-inducing alternative within the TB regimen.
Option A: Option A is incorrect. Rifampin has a major inducing interaction with imatinib, so doing nothing risks treatment failure.
Option B: Option B is incorrect. Induction lowers imatinib levels; a dose reduction would worsen the underexposure, the wrong direction.
Option C: Option C is incorrect. Co-administration is feasible with dose adjustment and monitoring (or a non-inducing alternative); stopping imatinib outright is not required and risks leukemia progression.
Option E: Option E is incorrect. The interaction is at the level of hepatic metabolism, so an intravenous route would not bypass CYP3A4 induction, and imatinib is an oral agent.
5. A CML patient loses response, and kinase-domain testing reveals the T315I gatekeeper mutation. The patient has established peripheral arterial disease and a prior myocardial infarction. Integrating the resistance mechanism with each candidate drug's toxicity profile, which choice best balances efficacy against this patient's vascular risk?
A) Switch to nilotinib, since its potency overcomes T315I and it is vascularly neutral
B) Continue imatinib at a higher dose, because vascular risk outweighs the need to address T315I
C) Switch to dasatinib, accepting that its pleural effusion risk is preferable to arterial events
D) Choose ponatinib without modification, since it is the only option for T315I and toxicity is not a consideration
E) Recognize that both ponatinib and asciminib have T315I activity, but ponatinib carries dose-dependent arterial occlusive events that are especially concerning in this vasculopath; asciminib, with a different toxicity profile, is the better-balanced choice (if ponatinib is unavoidable, use the lowest effective dose with aggressive cardiovascular risk management)
ANSWER: E
Rationale:
Option E is correct. T315I narrows the effective options to ponatinib (an ATP-competitive agent designed to bypass the gatekeeper) and asciminib (an allosteric STAMP inhibitor active against T315I at the higher 200 mg twice-daily dose). The integration step is matching that efficacy constraint to the patient's vascular risk: ponatinib's arterial occlusive events are dose-dependent and occur in a substantial fraction of patients, making it hazardous in someone with prior MI and peripheral arterial disease. Asciminib's distinct toxicity profile makes it the better-balanced choice here; if ponatinib must be used, the lowest effective dose with intensive cardiovascular risk reduction is required.
Option A: Option A is incorrect. Nilotinib does not overcome T315I and itself carries arterial occlusive and QTc risks, so it is doubly inappropriate.
Option B: Option B is incorrect. Dose-escalated imatinib does not overcome T315I, so leukemia control would be lost.
Option C: Option C is incorrect. Dasatinib does not have reliable T315I activity, so its toxicity trade-off is moot — it would not control the resistant clone.
Option D: Option D is incorrect. Asciminib is an equally valid T315I-active option, and toxicity absolutely is a consideration in a high vascular-risk patient, so ponatinib is not the only or unconsidered choice.
6. Two weeks into erlotinib therapy for EGFR-mutant NSCLC, a patient develops a moderate (grade 2) acneiform rash over the face and upper chest and asks whether the drug is failing or harming her. Integrating the mechanism of this rash with what it predicts and how it is managed, what is the most appropriate response?
A) The rash is an on-target effect of EGFR inhibition in the skin and a marker that the drug is engaging its target — a more pronounced rash is actually associated with better tumor response; continue erlotinib and manage the grade 2 rash with oral doxycycline (or minocycline) plus topical measures rather than stopping the drug
B) The rash indicates an allergic hypersensitivity reaction, so erlotinib must be discontinued permanently and never rechallenged
C) The rash signals that the tumor has become resistant, so therapy should be switched to osimertinib immediately
D) The rash means the drug is no longer reaching the tumor, so the erlotinib dose should be increased substantially
E) The rash is unrelated to erlotinib and should be referred to dermatology as an independent acne flare
ANSWER: A
Rationale:
Option A is correct. The acneiform rash arises from on-target inhibition of EGFR in the skin — the same action the drug exerts on the tumor — so it is an expected pharmacologic effect, not a failure or allergy. Integrating mechanism with prognosis: a more pronounced rash is associated with better tumor response and survival, so it can be reframed for the patient as a favorable sign of drug activity. Management follows the graded ladder: a grade 2 rash is treated with an oral tetracycline-class antibiotic (doxycycline or minocycline) plus topical care while continuing the drug; dose reduction is reserved for grade 3–4.
Option B: Option B is incorrect. The rash is a predictable on-target effect, not an allergic hypersensitivity reaction, and permanent discontinuation is not warranted for grade 2.
Option C: Option C is incorrect. The rash marks drug activity, not resistance, so an immediate switch to osimertinib is unjustified on this basis.
Option D: Option D is incorrect. The rash shows the drug is reaching and engaging EGFR; a large dose increase is inappropriate and would worsen toxicity.
Option E: Option E is incorrect. The rash is directly caused by erlotinib's EGFR inhibition; it is not an unrelated acne flare.
7. An EGFR-mutant NSCLC patient (exon 19 deletion) progresses after 13 months on erlotinib. Integrating the most common acquired resistance mechanism with the preferred diagnostic sequence and subsequent drug choice, what is the most appropriate next step?
A) Switch empirically to chemotherapy without molecular testing, since resistance mechanisms cannot guide therapy
B) Obtain an immediate surgical lung biopsy as the only acceptable way to assess resistance, then start osimertinib regardless of result
C) Test for the T790M resistance mutation, using plasma circulating tumor DNA as the preferred first approach; if T790M is detected, switch to osimertinib, and if the plasma result is uninformative, proceed to tissue rebiopsy before deciding
D) Increase the erlotinib dose to overcome the presumed T790M mutation
E) Add a BCR-ABL TKI such as nilotinib to the regimen to cover the resistant clone
ANSWER: C
Rationale:
Option C is correct. The most common acquired resistance mechanism to a first-generation EGFR TKI is the T790M mutation. The integrated workflow is: test for T790M, using plasma circulating tumor DNA (ctDNA) as the preferred, least invasive first approach; if T790M is detected, osimertinib is the indicated next agent because it was designed to inhibit the T790M-mutant receptor; and if the plasma test is uninformative (a negative plasma result does not exclude the mutation), proceed to tissue rebiopsy before deciding. This sequences the resistance mechanism, the diagnostic modality, and the drug selection into one coherent plan.
Option A: Option A is incorrect. Resistance testing does guide therapy here (T790M directs osimertinib), so abandoning testing forfeits an effective targeted option.
Option B: Option B is incorrect. Plasma ctDNA — not upfront surgical biopsy — is the preferred first test, and the drug choice should follow the result rather than being applied regardless.
Option D: Option D is incorrect. T790M is not overcome by raising the erlotinib dose; a T790M-active agent is required.
Option E: Option E is incorrect. The tumor remains EGFR-driven; a BCR-ABL agent such as nilotinib has no role in EGFR-mutant lung cancer.
8. Three weeks into osimertinib therapy, an EGFR-mutant NSCLC patient develops progressive dyspnea, dry cough, and low-grade fever, and a CT shows new diffuse bilateral ground-glass opacities without a new tumor mass. Integrating the severity of the suspected toxicity with the competing items on the differential, what is the correct immediate action?
A) Continue osimertinib and obtain a follow-up CT in three months, since bilateral opacities usually represent slow progression
B) Hold osimertinib immediately while evaluating, because the picture suggests drug-induced interstitial lung disease (ILD) — the most serious class toxicity — and delaying interruption increases the risk of fatal respiratory failure; the workup proceeds to exclude infection and progression, with systemic corticosteroids for confirmed or severe ILD
C) Increase the osimertinib dose, since worsening lung findings indicate the cancer is progressing and needs more drug
D) Continue osimertinib unchanged and add an inhaled bronchodilator for symptomatic relief
E) Switch immediately to an ALK inhibitor, which does not affect the lungs
ANSWER: B
Rationale:
Option B is correct. The combination of subacute dyspnea, cough, low-grade fever, and new diffuse bilateral ground-glass opacities without a new mass is the classic presentation of drug-induced ILD, the most serious class-wide toxicity of EGFR TKIs. Because ILD can progress rapidly to fatal respiratory failure and delayed interruption worsens that risk, the integrated response is to hold the drug immediately while the differential (infection, progression, embolism) is worked up, giving systemic corticosteroids for confirmed or severe disease. The severity of the toxicity drives an immediate-hold response rather than watchful waiting.
Option A: Option A is incorrect. Diffuse bilateral ground-glass opacities with these symptoms favor ILD, not slow progression, and watchful waiting on an unchanged drug is unsafe.
Option C: Option C is incorrect. The pattern points to drug toxicity, not progression; increasing the dose would intensify the ILD.
Option D: Option D is incorrect. A bronchodilator does not treat ILD, and continuing the offending drug leaves the patient at risk.
Option E: Option E is incorrect. Reflexively switching to an ALK inhibitor neither treats the lung process nor is appropriate for an EGFR-driven tumor; the priority is to hold the offending drug and evaluate.
9. An ALK-positive NSCLC patient on crizotinib has well-controlled disease in the chest and abdomen, but new brain metastases appear on surveillance imaging while systemic disease remains stable. Integrating crizotinib's pharmacokinetic limitation with the natural behavior of ALK-positive disease, how should this pattern be interpreted and managed?
A) This is systemic treatment failure, so crizotinib should be abandoned and the patient moved to palliative chemotherapy
B) This indicates transformation to small cell lung cancer and warrants immediate rebiopsy before any change
C) The brain metastases reflect an unrelated second primary cancer, so the ALK diagnosis should be questioned
D) This is the predictable CNS failure mode of crizotinib, which penetrates the CNS poorly while ALK-positive disease is prone to brain metastasis; the appropriate move is to switch to a CNS-penetrant ALK inhibitor such as alectinib (or lorlatinib) rather than concluding that ALK-directed therapy has failed systemically
E) The dose of crizotinib should simply be doubled to force more drug across the blood-brain barrier
ANSWER: D
Rationale:
Option D is correct. Integrating two facts explains the pattern: crizotinib penetrates the CNS poorly, and ALK-positive NSCLC has a strong propensity for brain metastasis. The result is isolated CNS progression while systemic disease stays controlled — the characteristic crizotinib failure mode, not a failure of ALK-directed therapy as a strategy. The correct management is to switch to a CNS-penetrant ALK inhibitor (such as alectinib or lorlatinib) that can control the brain disease, rather than abandoning ALK inhibition altogether.
Option A: Option A is incorrect. Systemic disease is controlled, so this is not systemic treatment failure, and moving to palliative chemotherapy discards an effective targeted strategy.
Option B: Option B is incorrect. Small cell transformation is an EGFR-resistance phenomenon, not the expected explanation for isolated CNS progression on crizotinib in ALK-positive disease.
Option C: Option C is incorrect. CNS progression here is the expected behavior of the known ALK-positive tumor under a poorly CNS-penetrant drug, not evidence of a separate primary cancer.
Option E: Option E is incorrect. Doubling crizotinib does not reliably overcome its intrinsic poor CNS penetration; switching to a CNS-penetrant agent is the rational solution.
10. A 29-year-old woman with ALK-positive NSCLC is about to start lorlatinib. She uses a combined oral contraceptive pill. Lorlatinib induces CYP3A4, the enzyme that metabolizes hormonal contraceptives, and the ALK TKI class is teratogenic. Integrating these two facts, what is the correct contraceptive counseling?
A) Because lorlatinib induces CYP3A4 and accelerates breakdown of hormonal contraceptives, the pill may fail; since the drug is teratogenic, she must use a reliable non-hormonal method — a copper intrauterine device or another non-hormonal barrier approach — during therapy
B) No contraception is needed because lorlatinib itself prevents pregnancy
C) The combined oral contraceptive remains fully reliable, so no change is required
D) She should simply double the dose of her oral contraceptive, which fully compensates for the induction effect
E) Contraception can be stopped once lorlatinib begins, since the drug is not harmful in pregnancy
ANSWER: A
Rationale:
Option A is correct. Two facts must be integrated. Lorlatinib induces CYP3A4, so it speeds the metabolism of hormonal contraceptives and lowers their levels, making a hormonal method unreliable. And because the ALK TKI class — lorlatinib included — is teratogenic, an unintended pregnancy could be harmed. Combining these, a hormonal method cannot be trusted, so a reliable non-hormonal option (a copper IUD or another non-hormonal barrier method) is required for the duration of therapy.
Option B: Option B is incorrect. Lorlatinib does not prevent pregnancy; it can harm a fetus, which is exactly why reliable contraception is needed.
Option C: Option C is incorrect. CYP3A4 induction reduces the reliability of the combined oral contraceptive, so it is not fully reliable here.
Option D: Option D is incorrect. Simply doubling a hormonal dose is not a recommended, dependable solution to enzyme induction; a non-hormonal method is advised.
Option E: Option E is incorrect. Lorlatinib is teratogenic, so contraception must continue rather than be stopped.
11. A patient on first-line osimertinib for EGFR-mutant NSCLC progresses after 18 months. A plasma circulating tumor DNA (ctDNA) panel is uninformative, and the patient now has rapidly worsening symptoms with a rising LDH and new liver lesions. Integrating the known heterogeneity of post-osimertinib resistance with the limits of liquid biopsy, what is the most appropriate next diagnostic step?
A) Restart the original first-generation EGFR TKI, since osimertinib resistance always reverts to T790M-driven disease
B) Perform a tissue rebiopsy, because resistance to first-line osimertinib is mechanistically heterogeneous (tertiary EGFR mutations such as C797S, bypass-pathway amplifications including MET and HER2, and histologic transformation to small cell lung cancer in roughly 15% of cases), and an uninformative plasma result combined with this clinical picture does not exclude a mechanism that only tissue can reveal, particularly histologic transformation
C) Conclude that no resistance mechanism is present and continue osimertinib unchanged
D) Switch directly to ponatinib, which covers all osimertinib resistance mutations
E) Assume MET amplification and start a MET inhibitor empirically without further testing
ANSWER: B
Rationale:
Option B is correct. Resistance to first-line osimertinib does not have a single dominant mechanism; it includes tertiary EGFR mutations such as C797S, bypass-pathway activation (MET and HER2 amplification), and histologic transformation to small cell lung cancer in approximately 15% of cases. A negative or uninformative plasma ctDNA result does not exclude these — and crucially, histologic transformation can only be diagnosed on tissue. Integrating the heterogeneity of resistance with the limitation of liquid biopsy, the correct next step is tissue rebiopsy, which the aggressive clinical picture (rising LDH, new visceral disease) further supports.
Option A: Option A is incorrect. Post-osimertinib resistance is heterogeneous and does not predictably revert to T790M; reflexively restarting a first-generation TKI is unfounded.
Option C: Option C is incorrect. Clear clinical and radiographic progression indicates a resistance mechanism is present; an uninformative plasma test does not mean none exists.
Option D: Option D is incorrect. Ponatinib is a BCR-ABL1 agent and does not cover EGFR resistance mutations; it has no role here.
Option E: Option E is incorrect. Empiric MET-inhibitor therapy without confirming the mechanism is inappropriate when several distinct mechanisms (including transformation) are possible and tissue can distinguish them.
12. A patient is starting afatinib, an irreversible pan-ErbB inhibitor that blocks EGFR and HER2. Integrating its mechanism with the resulting toxicity pattern, which anticipatory management plan is most appropriate?
A) Because afatinib spares wild-type EGFR, neither rash nor diarrhea is expected, so no anticipatory measures are needed
B) The dominant toxicity is QTc prolongation, so the plan centers on serial electrocardiograms
C) The dominant toxicity is pleural effusion, so the plan centers on echocardiographic surveillance
D) The principal risk is hypercholesterolemia, so a statin should be started prophylactically
E) Because afatinib's pan-ErbB activity inhibits EGFR in the skin (driving acneiform rash) and HER2 in the intestinal epithelium (driving diarrhea), and afatinib causes the most severe dermatologic and gastrointestinal toxicity of the EGFR TKIs, the plan should anticipate both — early loperamide at the first unformed stool with dose reduction for persistent diarrhea, and prophylactic or early doxycycline with topical care for the rash
ANSWER: E
Rationale:
Option E is correct. Afatinib's irreversible pan-ErbB mechanism predicts its toxicity directly: blocking EGFR in skin produces the acneiform rash, and blocking HER2 in intestinal epithelium disrupts chloride-secretion regulation and produces diarrhea. Because afatinib causes the most severe dermatologic and gastrointestinal toxicity in the class, anticipatory management should target both pathways — early loperamide at the first unformed stool (with dose reduction for persistent grade 2 or any grade 3 diarrhea) and prophylactic or early doxycycline plus topical measures for the rash. This is the integration of mechanism into a two-pronged supportive-care plan.
Option A: Option A is incorrect. Afatinib does not spare wild-type EGFR; it is irreversible and pan-ErbB, so it causes prominent rash and diarrhea, the very toxicities to anticipate.
Option B: Option B is incorrect. QTc prolongation is not afatinib's dominant toxicity; its hallmark effects are dermatologic and gastrointestinal.
Option C: Option C is incorrect. Pleural effusion is the signature toxicity of dasatinib, not afatinib.
Option D: Option D is incorrect. Near-universal hypercholesterolemia is characteristic of lorlatinib, not afatinib.
13. Across BCR-ABL, EGFR, and ALK-driven cancers, rational TKI sequencing requires integrating three variables at once: the specific resistance mutation present, whether the CNS must be covered, and the patient's toxicity constraints. Which single statement correctly applies this integrated framework across all three settings?
A) In every setting, the highest-potency agent should be chosen regardless of the specific mutation or CNS involvement
B) Resistance mutations should be ignored, and agents should be selected purely on the basis of the lowest toxicity profile
C) The correct agent is determined by matching the actual mutation and CNS need to the drug engineered for them while respecting toxicity limits: T315I-mutant CML calls for ponatinib or asciminib (favoring asciminib when arterial-occlusive risk is high), T790M-mutant EGFR disease calls for osimertinib, and ALK-positive disease with brain metastases calls for a CNS-penetrant agent such as alectinib or lorlatinib rather than crizotinib
D) CNS penetration is irrelevant to drug selection because all TKIs cross the blood-brain barrier equally
E) Once any resistance mutation appears, targeted therapy should be abandoned in favor of chemotherapy in all three diseases
ANSWER: C
Rationale:
Option C is correct. It applies the full framework simultaneously across the three families. The mutation dictates the mechanistic match — T315I requires ponatinib or asciminib, T790M requires osimertinib, and ALK resistance/CNS disease requires a CNS-penetrant ALK inhibitor; the CNS requirement adds penetration as a selection criterion (alectinib or lorlatinib over crizotinib for brain metastases); and the toxicity constraint refines the choice within the effective options (favoring asciminib over ponatinib when arterial-occlusive risk is high). Integrating all three variables, rather than any one alone, is what produces the correct sequencing decision.
Option A: Option A is incorrect. Raw potency does not substitute for matching the specific mutation and CNS need; the most potent drug can still be the wrong drug (for example, a potent agent inactive against T315I).
Option B: Option B is incorrect. Ignoring the resistance mutation and choosing on toxicity alone risks selecting an agent that cannot control the resistant clone.
Option D: Option D is incorrect. CNS penetration varies markedly among TKIs (crizotinib is poor, alectinib and lorlatinib are high), so it is a real and decisive selection factor.
Option E: Option E is incorrect. In each disease, a later-generation targeted agent specifically restores control against the relevant resistance mechanism, so abandoning targeted therapy is the wrong general rule.
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