01Purpose and principlesWhat the treatment does and how it fits into care.
Targeted medicines include kinase inhibitors, monoclonal antibodies, antibody-drug conjugates, angiogenesis inhibitors and agents exploiting repair defects. Their use follows a predictive marker validated in a particular cancer and line of therapy. A mutation that drives one tumour may not be actionable in another, and a variant of uncertain significance is not a treatment biomarker. Pathology, stage, prior treatment and national access criteria remain essential.
Oral agents require the same governance as infused SACT. Absorption may depend on food or gastric pH; CYP enzymes and transporters create interactions; adherence can fluctuate because chronic toxicity is taken home. Monoclonal antibodies can cause infusion reactions and target-specific cardiac, pulmonary, skin or gastrointestinal injury. Antiangiogenic therapy creates hypertension, proteinuria, bleeding, thrombosis, impaired wound healing and rare perforation.
Response is assessed with standard clinical and imaging measures. At progression, verify exposure and adherence before assuming resistance. Repeat biopsy can identify transformation or a new actionable mechanism when the result would change care. Treatment should stop for clear progression, unacceptable toxicity or changed goals according to the protocol rather than continuing because the target remains detectable historically.
Key points
- Targeted therapy inhibits a tumour dependency, receptor, kinase, repair defect or angiogenic pathway; the presence of a biological target does not guarantee clinical benefit.
- The biomarker, assay, specimen, disease stage and licensed or recommended indication must all match before treatment begins.
- Small-molecule inhibitors often have oral absorption, food, acid-suppression and enzyme-interaction issues, while monoclonal antibodies add infusion and immune-mediated risks.
- Class effects include rash, diarrhoea, hypertension, hepatotoxicity and cardiac dysfunction, but toxicity differs substantially by target and agent.
- Baseline ECG, echocardiography, blood pressure, urinalysis, viral testing, eye review or lung assessment is selected from the actual medicine, not applied indiscriminately.
- A correct oral dose still fails when vomiting, non-adherence or interacting medicines reduce exposure; reconcile all prescriptions, supplements and food restrictions.
- Progression can reflect target loss, secondary mutation, bypass signalling, histological transformation or sanctuary-site disease and may justify repeat tissue or circulating DNA.
- Provide explicit hold and emergency rules for severe rash, diarrhoea, breathlessness, chest pain, jaundice, visual change and uncontrolled hypertension.
02Indications, selection and cautionsWho may benefit, who needs urgent treatment and important alternatives.
A pathogenic alteration or protein result has evidence and approval for this tumour type, stage and treatment line.
Rash, diarrhoea, hypertension or another mechanism-linked effect may indicate exposure but does not prove tumour response.
New pneumonitis, cardiomyopathy, severe hypertension, hepatitis, perforation or ocular injury requires urgent interruption and specialist assessment.
Acid suppression, enzyme induction, supplements, food or missed oral doses can reduce or increase drug exposure.
Progression after response may reflect secondary target change, bypass signalling or histological transformation rather than loss of every treatment option.
03Assessment before treatmentTests and checks that guide safe selection.
Read from the initial assessment onwards. Tests may run in parallel in urgent care; first-line, preferred, confirmatory, definitive and gold-standard labels appear only when the chapter explicitly states them.
- 01
Validated tumour biomarker assayFirst step - Why
- Confirm eligibility for the specified targeted medicine.
- Interpretation and limitations
- Review pathogenicity, tumour content, platform and indication; a negative result is limited to the assay's detectable alteration classes.
- 02
Baseline organ-specific tests - Why
- Measure reserve in tissues vulnerable to the selected agent.
- Interpretation and limitations
- Use ECG, echocardiography, blood pressure, renal, hepatic, urine, eye or lung testing only as required by product and protocol.
- 03
Medication and supplement reconciliation - Why
- Identify pharmacokinetic and pharmacodynamic interactions before dosing.
- Interpretation and limitations
- Include acid suppression, herbal products, anticoagulants and food requirements; specialist pharmacy should advise rather than guessing dose separation.
- 04
Response imaging - Why
- Determine objective benefit at the protocol-defined interval.
- Interpretation and limitations
- Compare with baseline and integrate symptoms; inflammatory or cystic change may require disease-specific response interpretation.
- 05
Repeat tissue or circulating DNA - Why
- Investigate a treatment-changing resistance mechanism.
- Interpretation and limitations
- Circulating DNA can be falsely negative with low shedding, while tissue is preferred when transformation is possible.
04Treatment approachPreparation, options, escalation and aftercare.
01MatchValidate target and contextFirst stepA tumour report identifies a potentially actionable alteration.+
- 1Confirm histology, stage, line, assay and exact biomarker meet the national protocol or access criteria.
- 2Review organ reserve, interactions, pregnancy and prior toxicities and explain absolute benefit and uncertainty.
- 3Prescribe through SACT governance with agent-specific baseline tests, supportive medicines and emergency hold instructions.
02MaintainProtect exposure and safetyTargeted treatment continues between oncology visits.+
- 1Review adherence, food timing, vomiting, interacting medicines and supplements at every cycle or dispensing contact.
- 2Trend blood pressure, ECG, cardiac, renal, hepatic, urine, skin, bowel or eye measures required for the agent.
- 3EscalationHold and escalate serious organ toxicity promptly, then restart or reduce only through the current product and protocol rules.
03ResistClarify progressionCancer worsens after an initial response or stable interval.+
- 1Confirm objective progression and adequate exposure, excluding adherence failure and an imaging mimic.
- 2Obtain repeat molecular or histological assessment when transformation or a resistance alteration would change therapy.
- 3Switch, combine, trial or stop treatment according to evidence, organ reserve and goals rather than target presence alone.
05Regimens, contraindications and interactionsTreatment details and the circumstances that modify them.
Imatinib
400 mg orally once daily with a meal and a large glass of water is a common licensed starting dose for chronic-phase BCR::ABL1-positive CML and for unresectable or metastatic KIT-positive GIST; other phases, indications and responses use different protocol doses.Confirm the precise biomarker and indication; monitor full blood count, liver function, oedema, cardiac risk and interactions with CYP3A4 modulators. Adjust or hold only through the disease protocol and product information.
Subcutaneous trastuzumab
600 mg subcutaneously every 3 weeks, with no loading dose, for a licensed HER2-positive breast-cancer protocol; intravenous trastuzumab uses a different weight-based schedule and must not be substituted by assumption.Confirm HER2 eligibility and product/formulation, monitor left-ventricular function, and manage injection reactions, pulmonary symptoms and pregnancy risk. Anthracycline sequence materially affects cardiac risk.
06Complications, monitoring and follow-upAdverse effects, response and longer-term review.
- Track adherence and dispensing with explicit food, acid-suppression and interaction review for every oral agent.
- Measure the exact organ parameters required by product information before treatment and at protocol-defined intervals.
- Record toxicity grade, dates held, dose changes and recovery so later prescribers do not restore an unsafe dose automatically.
- Assess response against baseline and stop or change therapy when progression or burden outweighs benefit.
- At resistance review, document whether repeat molecular testing can realistically open a funded treatment or trial.
07Special situationsVariants, exceptions and circumstances that change the usual approach.
Target needs context
A mutation is actionable only where a validated assay and tumour-specific outcome evidence support the medicine.
Oral is still SACT
Home administration shifts observation to the patient but does not reduce interaction, teratogenic or organ-toxicity risk.
Class does not equal agent
Medicines aimed at related targets can have different selectivity, food rules, half-lives and serious adverse effects.
Adherence can mimic resistance
Before ordering a resistance biopsy, confirm that the prescribed medicine has actually been absorbed and taken consistently.
Transformation needs tissue
A molecular liquid result may miss a changed histological phenotype that requires a fundamentally different treatment.
08Common pitfallsFrequent interpretation and management errors.
- 01
Treating a variant of uncertain significance.
- 02
Ignoring tumour type and treatment-line context.
- 03
Calling oral treatment low risk.
- 04
Missing acid, food and enzyme interactions.
- 05
Treating toxicity without holding the causal drug.
- 06
Assuming progression always means target loss.