Targeted Therapy & Biologics

Unlike traditional chemo that attacks all rapidly dividing cells, targeted therapies hit specific molecular targets — but their unique toxicities catch students off guard because they don't look like typical chemo side effects.

Targeted therapies and biologics work by blocking specific proteins or pathways that cancer cells depend on for growth and survival. Monoclonal antibodies (suffix -mab, e.g., trastuzumab, rituximab) bind extracellular targets like HER2 or CD20 receptors. Small-molecule inhibitors (suffix -nib, e.g., imatinib) block intracellular signaling pathways like tyrosine kinases; proteasome inhibitors (suffix -mib, e.g., bortezomib) use a different mechanism but are also targeted agents. Because these agents target specific molecules, their side effect profiles differ from traditional cytotoxic chemotherapy. Key toxicities to know: trastuzumab carries cardiotoxicity risk (monitor LVEF before and during treatment — hold if LVEF drops significantly); rituximab can trigger severe infusion reactions and reactivate hepatitis B; tyrosine kinase inhibitors commonly cause skin rashes, diarrhea, and hepatotoxicity (monitor LFTs). Infusion reactions — fever, chills, rigors, hypotension, bronchospasm — are a hallmark concern with monoclonal antibodies, especially during the first dose. Slow the rate or stop the infusion and administer premedications (acetaminophen, diphenhydramine, corticosteroids) per protocol. Targeted therapies are less likely to cause the severe myelosuppression or alopecia associated with traditional chemo, though clinically significant cytopenias can occur with some agents (e.g., rituximab, imatinib).

Key Distinctions

Don't confuse targeted therapy side effects (infusion reactions, skin rash, cardiac monitoring) with traditional chemo toxicities (nadir, neutropenia, mucositis) — those belong to sibling atoms. Students mix up trastuzumab cardiotoxicity with doxorubicin cardiotoxicity: trastuzumab damage is often reversible and not dose-cumulative, while doxorubicin causes irreversible dose-dependent cardiomyopathy. The suffix matters: -mab is a monoclonal antibody (IV infusion, watch for infusion reactions), -nib is a kinase inhibitor (usually oral, watch liver function), -mib is a proteasome inhibitor (different mechanism from kinase inhibitors).

Clinical Pearl

First infusion, first danger. With monoclonal antibodies, stay at the bedside during the initial infusion — most severe reactions happen with dose one, not dose ten.