Monoclonal antibodies and biologics in oncology

Naming, mechanisms, antibody–drug conjugates, bispecifics, infusion reactions, class toxicities and biosimilars: a working primer

For clinicians and students · Special tutorial · Across cancers · 9 min read · last reviewed September 30, 2026

Why a primer

Monoclonal antibodies (mAbs) now appear in most solid tumour and hematologic regimens. Their toxicities differ from cytotoxic chemotherapy: they are often on-target, sometimes delayed, and often managed by holding the drug rather than reducing the dose. This primer covers the class-level concepts that make each regimen tutorial easier to follow. This page gives no dosing. Doses are in the regimen tutorials and in your institution's protocols.

Reading the name

Most therapeutic antibodies end in -mab. For agents named under the long-standing International Nonproprietary Name (INN) scheme, the stem before -mab tells you the species source, and an infix tells you the target class:

Two cautions:

1. The naming scheme changed. Since 2017 the WHO INN programme has dropped the species stem. Since 2021–22 it has used new suffixes that replace "-mab" altogether: -tug (unmodified immunoglobulin), -bart (artificial/engineered), -mig (multi-specific, e.g. bispecifics) and -ment (fragments). Newer agents therefore may not decode the old way.
2. Prefixes are arbitrary. Names such as ado-trastuzumab emtansine or fam-trastuzumab deruxtecan contain extra words that identify a different drug. eviQ explicitly warns that trastuzumab must not be substituted with T-DM1 or T-DXd.

Mechanisms of action

Target expression matters. HER2 antibodies need HER2 amplification or overexpression. The exception is T-DXd, which has activity in "HER2-low" disease through its membrane-permeable payload (see below). Anti-EGFR antibodies in colorectal cancer need RAS wild-type tumours, because a downstream mutation makes blocking the receptor irrelevant.

Antibody–drug conjugates (ADCs)

An ADC has three parts: antibody + linker + payload. The drug-to-antibody ratio (DAR), the stability of the linker, and whether the payload can cross membranes (the "bystander effect" on neighbouring cells with low or no antigen expression) determine both how active the drug is and how toxic. As a rule, ADC toxicity looks like the payload, not the antibody.

T-DXd ILD management (BC Cancer BRAVENH)

• A baseline CT chest is required. Active ILD/pneumonitis is an exclusion.
• Grade 1 (asymptomatic): delay until the pneumonitis resolves. If it resolves within 28 days, keep the dose; otherwise reduce one level. Consider corticosteroids.
• Grade ≥ 2 (symptomatic): permanently discontinue, and start corticosteroids straight away (e.g. prednisone ≥ 1 mg/kg/day or equivalent). Continue steroids for at least 14 days, then taper over at least 4 weeks.
• Teach patients to report new cough, dyspnea or fever promptly.

Bispecific T-cell engagers

T-cell engagers cause two characteristic toxicities:

• Cytokine release syndrome (CRS): fever, hypotension, hypoxia. It is most common with the first doses.
• Immune effector cell-associated neurotoxicity syndrome (ICANS): confusion, dysphasia, tremor, seizures, reduced consciousness.

Protocols reduce the risk with step-up dosing, premedication (corticosteroid, antihistamine, antipyretic) and inpatient or close observation for the early doses. CRS is graded (commonly by ASTCT consensus criteria) and treated with supportive care, tocilizumab and corticosteroids. ICANS is treated with corticosteroids. Prolonged cytopenias, hypogammaglobulinemia and serious infections are also class effects, particularly with BCMA-directed agents. Follow the product-specific protocol exactly: step-up doses and observation windows differ between drugs.

Infusion reactions and premedication

• Mechanism. Most first-dose reactions are cytokine-release (non-IgE) reactions: fever, rigors, flushing, dyspnea and hypotension, usually during the first infusion. They become less frequent with later doses. True IgE-mediated anaphylaxis is less common. A notable exception is cetuximab, where severe first-dose anaphylaxis is linked to pre-existing IgE against galactose-α-1,3-galactose (alpha-gal).
• Frequency examples.
• BC Cancer reports chills and fever in about 40% of patients at the first trastuzumab infusion. Serious reactions occur in about 3 per 1000.
• Panitumumab (a fully human IgG2) causes severe reactions in about 1%. Late-onset reactions also occur, so warn patients.
• Standard mitigations.
• A slower first infusion, then rate escalation when tolerated. For example, trastuzumab loading over 90 min, then 30 min for later doses; panitumumab 60 min, then 30 min.
• Premedication where the protocol specifies it. For example, eviQ gives an antihistamine plus dexamethasone before cetuximab. Rituximab protocols commonly use acetaminophen plus an antihistamine, with or without a steroid.
• Post-infusion observation for the early doses.
• Managing a reaction.
• Stop the infusion and assess the ABCs.
• Give an antihistamine, steroid and antipyretic as needed. Use epinephrine and bronchodilators for anaphylaxis.
• For mild or moderate reactions, restart at a reduced rate once symptoms resolve.
• For severe reactions, discontinue permanently.
• Record the reaction and add premedication for future doses.

Class toxicities you must monitor

HER2-directed antibodies (trastuzumab, pertuzumab, HER2 ADCs)

• Cardiotoxicity. Usually an asymptomatic fall in LVEF, sometimes heart failure. It is mostly reversible and not cumulative-dose-dependent, unlike anthracycline cardiomyopathy.
• In the pivotal metastatic trial (Slamon 2001), giving trastuzumab together with an anthracycline caused unacceptable cardiac dysfunction. Regimens now give the two sequentially, or avoid anthracyclines altogether.
• Monitoring. LVEF (echo or MUGA) at baseline and about every 3 months during curative-intent therapy. BC Cancer requires no more than 4 months between assessments.
• Management. The antibody is held, not dose-reduced. Repeat LVEF in 3–4 weeks. Discontinue after repeated holds or with symptomatic heart failure (BC Cancer BRAJDCARBT; eviQ 3736).
• Trastuzumab may raise the INR on warfarin.

Anti-VEGF (bevacizumab; also ramucirumab and aflibercept as related agents), from BC Cancer GIFFIRB:

• Hypertension. Check BP before every dose, and after the dose for the first 3 cycles. Treat with calcium channel blockers, ACE inhibitors or diuretics. Discontinue for hypertensive crisis or hypertension that cannot be controlled.
• Proteinuria. Dipstick every second cycle. If 2+ or more, collect a 24-h urine. Hold at > 2 g/24 h; discontinue at > 4 g/24 h.
• Bleeding. Stop for grade 3–4 hemorrhage. Avoid NSAIDs and ASA > 325 mg/day.
• Arterial thromboembolism, with higher risk at age > 65 or with prior events.
• GI perforation and wound dehiscence. Exclude patients within 28 days of major surgery, and plan elective surgery around dosing.
• PRES/RPLS.

Anti-EGFR antibodies (cetuximab, panitumumab), from BC Cancer GIFFIRPAN:

• Papulopustular rash. Face and upper trunk, peaking around week 2. Pre-emptive doxycycline or minocycline plus topical clindamycin/hydrocortisone from day 1 reduced grade ≥ 2 rash in STEPP.
• For grade 3 rash, withhold, then resume at stepwise lower doses. Discontinue for grade 4.
• Paronychia, xerosis, fissures and trichomegaly.
• Hypomagnesemia. Can be delayed beyond 6 weeks. Check magnesium before each dose and replace orally or IV.
• Rare interstitial lung disease.

CD20 antibodies (rituximab, obinutuzumab)

• First-infusion reactions. The risk is highest when the circulating lymphocyte count is high.
• Hepatitis B reactivation. Screen for HBsAg and anti-HBc before starting, and give prophylaxis or monitoring per local policy.
• Hypogammaglobulinemia and infections.
• Rare progressive multifocal leukoencephalopathy.

Checkpoint inhibitors

• Immune-related adverse events (colitis, hepatitis, pneumonitis, endocrinopathies, and others). These are covered in the dedicated checkpoint-inhibitor irAE tutorial.

Biosimilars

• A biosimilar is a biologic that is highly similar to an approved reference product, with no clinically meaningful differences in safety, purity or potency. It is not a generic. Biologics are made in living cells, so exact copies are impossible and batch-to-batch microheterogeneity exists even for the originator.
• Approval rests mainly on analytical and functional comparability, pharmacokinetic equivalence, and usually one confirmatory clinical trial in a sensitive population. Approval in other indications is then extrapolated.
• In oncology, biosimilars of trastuzumab, bevacizumab and rituximab (and supportive-care biologics such as filgrastim and pegfilgrastim) are widely used. Many Canadian provinces and other jurisdictions mandate switching to biosimilars for cost reasons.
• Naming and traceability. US biosimilars carry a four-letter suffix (e.g. trastuzumab-xxxx). Other jurisdictions rely on brand name and lot number. Record the brand and lot for pharmacovigilance.
• Practical cautions.
• Reconstitution, concentration and vial sizes may differ from the originator. Pharmacy must confirm product-specific preparation.
• Do not interchange subcutaneous and IV formulations without the specific protocol. For example, SC trastuzumab is a fixed 600 mg dose every 3 weeks (per eviQ), not a weight-based dose.
• Explain the switch to patients to limit "nocebo" effects.

Clinical pearls

• Hold, don't reduce. Most toxicities from naked antibodies (LVEF decline, proteinuria, rash) are managed by holding and then resuming. Exceptions such as the panitumumab rash schedule and ADC dose levels are written into specific protocols.
• Watch for look-alike names. Trastuzumab, ado-trastuzumab emtansine, fam-trastuzumab deruxtecan and trastuzumab SC are four different orders. Check the full name and the dose units (mg/kg vs mg).
• Loading doses reset after long gaps. For trastuzumab and pertuzumab, a delay of more than 6 weeks means reloading (eviQ; BC Cancer for trastuzumab).
• Weight-based dosing needs current weights. BC Cancer recalculates bevacizumab if body weight changes by more than 10%.
• Ask about new cough on T-DXd. Early detection of ILD is the single most important safety measure for this drug.
• Bispecifics need systems, not just orders: step-up calendars, observation beds, tocilizumab availability, and a wallet card for CRS and ICANS symptoms.

Educational material for health professionals and students. Not a prescribing order; it does not replace your institution's approved protocol, pharmacy verification or clinical judgement.

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