Targeted therapy is a type of cancer treatment that works by attacking specific molecules involved in cancer cell growth and survival, rather than killing all rapidly dividing cells the way traditional chemotherapy does. It represents a shift toward precision medicine, where treatment is matched to the biological characteristics of an individual’s tumor. Targeted therapies can block growth signals, cut off a tumor’s blood supply, trigger cancer cell death, or deliver toxic substances directly to cancer cells while largely sparing healthy tissue.
How Targeted Therapy Differs From Chemotherapy
Traditional chemotherapy works by interfering with all rapidly dividing cells in the body. That includes cancer cells, but also hair follicles, the lining of the digestive tract, and bone marrow, which is why chemotherapy often causes hair loss, nausea, and immune suppression. Targeted therapy takes a different approach: it zeroes in on specific molecules that cancer cells rely on to grow and spread.
Cancer cells typically have mutations or overactive proteins that drive their uncontrolled growth. Targeted drugs are designed to interfere with those exact molecules. A tumor that grows because it overproduces a particular growth receptor, for instance, can be treated with a drug that blocks that receptor specifically. Healthy cells that don’t depend on that receptor are mostly left alone. This selectivity doesn’t eliminate side effects entirely, but it changes the profile of those side effects significantly.
The Two Main Types of Targeted Drugs
Most targeted therapies fall into one of two categories: monoclonal antibodies and small-molecule drugs. The distinction matters because it determines how each drug reaches its target and how you receive it.
Monoclonal antibodies are large, complex proteins (about 150 kilodaltons) made up of four polypeptide chains. They work on targets found on the surface of cancer cells because they’re too large to enter the cell. Their size gives them an advantage in precision: they bind to their target with high selectivity and produce fewer “off-target” effects compared to most small-molecule drugs. Because they break down rapidly in the gut, they can’t be taken as pills. They’re given by intravenous infusion or injection, typically one to four times per month.
Small-molecule drugs are much smaller and can slip inside cancer cells to reach targets within the cell’s interior, such as enzymes involved in signaling pathways. These are usually taken as daily oral pills at a flat dose, which makes them more convenient for long-term use. Some patients take them for months or years as maintenance treatment.
There’s also a hybrid approach called antibody-drug conjugates. These use a monoclonal antibody as a delivery vehicle to carry a potent toxic compound directly to the cancer cell. The antibody binds to a receptor on the cell surface, gets pulled inside, and releases the toxic payload once it reaches the cell’s interior compartments.
What These Drugs Actually Target
Targeted therapies can be grouped by what they do at the molecular level. Signal transduction inhibitors block the chain of chemical messages that tell a cancer cell to divide. Angiogenesis inhibitors cut off the blood supply tumors need to grow. Apoptosis inducers trigger programmed cell death, essentially flipping the self-destruct switch that cancer cells have learned to ignore. Hormone therapies starve hormone-sensitive cancers of the signals they depend on.
Some of the most well-established targets include the epidermal growth factor receptor (EGFR), HER2, and BRAF. EGFR-targeting drugs are now standard treatment for non-small cell lung cancer (in patients whose tumors carry specific EGFR mutations), colorectal cancer, pancreatic cancer, and head and neck cancers. HER2-targeting drugs are widely used in breast cancer and were recently approved for biliary tract cancer. BRAF inhibitors have transformed the treatment of melanoma, though interestingly, colon cancers with the same BRAF mutation respond poorly to the same drugs. The same genetic mutation doesn’t always mean the same treatment will work, because the surrounding biological context of the tumor matters.
Biomarker Testing: Finding Out If You’re a Candidate
Before starting targeted therapy, your tumor needs to be tested to identify whether it has the specific molecular features a drug is designed to attack. This process is called biomarker testing, and it’s a required step for most targeted treatments.
Testing can range from a simple single-marker test (checking whether a breast tumor overexpresses HER2, for example) to broad genomic panels that analyze dozens or even hundreds of genes at once using next-generation sequencing. For lung cancer patients, testing for EGFR mutations and ALK gene rearrangements is now routine before choosing a first-line treatment. Studies have shown that this test-then-treat approach is more cost-effective than jumping straight to standard chemotherapy.
The results of biomarker testing determine your treatment options. If your tumor doesn’t carry a targetable mutation, targeted therapy may not be appropriate, and other approaches like chemotherapy or immunotherapy would be considered instead. Some patients are also tested again if their cancer progresses, because tumors can acquire new mutations over time that open the door to different targeted drugs.
Side Effects of Targeted Therapy
Targeted therapies cause fewer of the classic chemotherapy side effects, but they have their own distinct set of reactions. Skin problems are among the most common. Drugs targeting EGFR frequently cause a characteristic acne-like rash of papules and pustules on the face and upper body, along with dry skin, nail inflammation (paronychia), itching, and changes in hair growth. This cluster of skin reactions is so predictable that it has its own name in clinical literature. Oral sores, mucositis, and sun sensitivity also occur with EGFR-targeting drugs.
Drugs that target blood vessel growth (through VEGFR or PDGFR pathways) commonly cause high blood pressure and diarrhea, along with skin reactions from direct vascular effects. Hand-foot syndrome, which causes painful redness, swelling, and peeling on the palms and soles, is the most frequent skin reaction with certain small-molecule inhibitors.
BRAF inhibitors bring their own profile: rashes, sun sensitivity, dry skin, and sometimes the development of new skin growths including benign keratoses and, in some cases, squamous cell carcinomas that need to be monitored and removed. When BRAF inhibitors are combined with MEK inhibitors (a common pairing), fever becomes the most significant side effect and sometimes requires dose adjustments. Changes in skin or hair color can also occur with some drugs, though these tend to reverse within about a month after stopping treatment.
Why Targeted Therapy Can Stop Working
One of the biggest challenges with targeted therapy is that cancers can develop resistance over time. This happens through several mechanisms. The cancer cells may mutate the very protein the drug targets, changing its shape so the drug no longer binds effectively. They may activate alternative signaling pathways that bypass the blocked target entirely, like rerouting traffic around a roadblock. They can also ramp up activity in pathways upstream or downstream of the target, or activate broader survival mechanisms that keep the cell alive despite the drug’s effects.
Resistance is the reason many patients respond well to targeted therapy initially but eventually see their cancer progress. To combat this, researchers have developed next-generation drugs designed to work against resistant mutations. Osimertinib, for example, was specifically developed to treat lung cancers that developed a particular resistance mutation (T790M) after treatment with earlier EGFR-targeting drugs. Combination strategies, using two or more targeted drugs that hit different pathways simultaneously, are another approach to prevent or delay resistance.
A Rapidly Expanding Field
The number of available targeted therapies has grown substantially. In 2024 alone, the FDA approved targeted drugs for lung cancer, breast cancer, biliary tract cancer, stomach cancer, leukemia, brain tumors (including a pediatric low-grade glioma drug), bladder cancer, esophageal cancer, small cell lung cancer, and a rare blood disorder. Some of these approvals represent first-ever targeted options for cancers that previously had limited treatment choices.
The breadth of these approvals reflects a broader shift in oncology. As genomic testing becomes more routine and more targetable mutations are identified, the pool of patients who can benefit from targeted therapy continues to grow. For cancers that have well-characterized molecular drivers, targeted therapy has become a cornerstone of treatment, often used as first-line therapy or in combination with chemotherapy or immunotherapy to improve outcomes.