Targeted Therapy is a form of cancer treatment designed to interfere with specific molecular features that help malignant cells survive, proliferate, invade tissues or evade normal regulatory mechanisms. Unlike treatments that primarily distinguish cancer from normal tissue by differences in cell division rates, targeted approaches seek identifiable molecular targets such as abnormal proteins, mutated enzymes, amplified receptors, fusion proteins or signalling components. The term therefore describes a therapeutic strategy rather than one single drug class. The National Cancer Institute describes targeted therapy as treatment directed at proteins controlling cancer-cell growth, division and spread, and regards it as a foundation of precision medicine.
Targeted Therapy generally depends on identifying a biomarker that indicates the presence or activity of a therapeutically actionable target. Biomarkers can be detected in tumour tissue, blood or other biological specimens using methods such as immunohistochemistry, DNA sequencing, RNA analysis, fluorescence-based assays or broader genomic profiling. A target may be a cell-surface receptor, intracellular kinase, DNA-repair mechanism, metabolic dependency or other molecular process.
The practical implication is that two patients with the same anatomical cancer may receive different systemic treatments because their tumours have different molecular characteristics, while a patient with a particular biomarker may potentially receive the same targeted treatment even when the cancer originated in a different anatomical site.
Two broad technological categories dominate Targeted Therapy: small-molecule drugs and monoclonal antibodies. Small molecules can enter cells and therefore commonly inhibit intracellular enzymes or signalling proteins, whereas monoclonal antibodies are larger biological agents that generally bind extracellular or cell-surface targets. Some agents inhibit a single molecular target directly, while others affect interconnected signalling networks or deliver a toxic payload to cells expressing a particular antigen. Antibody-drug conjugates illustrate the latter principle by combining molecular recognition with a cytotoxic payload. Targeted therapies can therefore function through receptor blockade, kinase inhibition, protein degradation, immune-mediated mechanisms, disruption of DNA repair, interference with signalling cascades or selective delivery of therapeutic substances.
Targeted Therapy is particularly important where a tumour contains a driver alteration on which its growth depends. Examples include inhibition of BCR-ABL in particular leukaemias, HER2-directed treatment in HER2-positive breast cancer, and EGFR-directed treatment in subsets of lung cancer carrying activating EGFR alterations. Other clinically relevant targets include particular alterations involving ALK, ROS1, BRAF, RET, MET, NTRK, KRAS and other molecular pathways, depending on tumour type and the therapeutic indication.
In breast cancer, targeted options can include HER2-directed drugs, CDK4/6 inhibitors used in appropriate hormone-receptor-positive disease, and PARP inhibitors for selected cancers with BRCA1 or BRCA2 alterations. These examples demonstrate that the usefulness of a target depends on the precise biological and clinical context rather than merely on the presence of a gene name.
An important limitation of Targeted Therapy is acquired or intrinsic resistance. A tumour may never respond because the supposed target is not sufficiently important to its biology, or it may initially respond and subsequently progress after cancer cells acquire additional alterations, activate alternative signalling pathways, alter drug metabolism, change the target itself or develop other mechanisms that bypass the treatment. Tumours are also heterogeneous, meaning that different populations of malignant cells within the same tumour may carry different molecular characteristics. Consequently, a treatment can eliminate sensitive cells while resistant populations remain. Combination treatment, sequential treatment and repeat molecular testing may therefore become relevant when disease progresses, although the appropriate strategy varies substantially by cancer and individual circumstances.
Targeted Therapy is not synonymous with harmless therapy or with treatment that affects only malignant cells. Molecular targets may also occur in healthy tissues, and interference with normal biological pathways can produce clinically significant adverse effects. Depending on the drug, toxicities can involve the skin, gastrointestinal system, liver, heart, lungs, bone marrow, kidneys or other organs. Monoclonal antibodies and other biologics can also produce infusion reactions or immune-mediated complications. Drug interactions and effects on normal signalling pathways can influence tolerability. The term “targeted” therefore describes the biological specificity of the treatment mechanism, not an absence of toxicity. Appropriate selection involves balancing molecular rationale, evidence of efficacy, disease characteristics, previous treatment, comorbidities, potential interactions and patient-specific factors.
Targeted Therapy has changed cancer treatment by linking therapeutic development more closely to tumour biology. Historically, oncology often organised treatment principally around anatomical location and microscopic appearance, whereas molecular classification increasingly identifies biologically distinct subgroups within a conventional tumour category. This transition has required developments in pathology, molecular diagnostics, sequencing, drug development, clinical-trial design and regulatory science. Basket trials, umbrella trials and biomarker-selected studies can evaluate treatments according to molecular characteristics rather than relying exclusively on anatomical tumour site. The approach also illustrates the reciprocal relationship between diagnostics and therapeutics: discovery of a molecular alteration can stimulate drug development, while availability of an effective drug creates clinical value for accurately identifying the alteration.
Targeted Therapy should be distinguished from conventional cytotoxic chemotherapy, hormone-based treatment and immunotherapy, although boundaries can overlap. Some hormone therapies are themselves considered a form of targeted treatment because they interfere with hormonal signalling, while some targeted agents influence immune mechanisms or are combined with immunotherapy.
Targeted treatment also does not necessarily mean personalised treatment in the broadest sense; a drug may be targeted to a biomarker shared by thousands of patients, while precision medicine incorporates that information alongside disease stage, clinical characteristics and other factors. In practice, targeted agents may be used before surgery, after surgery, with radiation or chemotherapy, or as treatment for advanced disease. Their role depends on the cancer subtype, molecular findings, evidence base and treatment setting.
