Targeted therapies act on specific molecular features that drive a cancer’s growth, rather than attacking all dividing cells the way chemotherapy does. They include small-molecule inhibitors taken as pills (for example EGFR, ALK, BRAF or kinase inhibitors, and PARP inhibitors) and monoclonal antibodies given by infusion (such as HER2- or VEGF-directed antibodies). Because they depend on a target, they usually require biomarker testing (molecular/genomic profiling of the tumor) to find patients most likely to benefit. Angiogenesis inhibitors, a subset, choke off a tumor’s blood supply. Targeted drugs can be dramatically effective but cancers may develop resistance over time.
As daily pills or as IV infusions, depending on the drug, usually continued as long as it keeps working and side effects are manageable. Tumor biomarker testing guides which targeted drug (if any) is appropriate, and response is followed with scans and sometimes blood-based (circulating-tumor-DNA) testing.
Many targeted drugs are taken long-term at home. Side effects differ by drug and are often different from chemotherapy (e.g., rash, diarrhea, blood-pressure or liver changes). When resistance develops, testing may reveal a new target and a switch in therapy.