Targeted therapy is a type of cancer treatment that works by attacking specific molecules involved in tumor growth, rather than killing all rapidly dividing cells the way chemotherapy does. Where chemotherapy directly interferes with cell division and depends on triggering cell death in any fast-growing cell, targeted drugs zero in on the genetic changes or proteins that make cancer cells different from normal ones. This precision generally means fewer side effects, though targeted therapy comes with its own challenges, including the possibility that cancer cells find ways to resist treatment over time.
How Targeted Therapy Differs From Chemotherapy
Chemotherapy is a blunt instrument. It uses potent chemicals that damage or destroy cells in the process of dividing, regardless of whether those cells are cancerous or healthy. That’s why chemo causes familiar side effects like hair loss and nausea: hair follicles, gut lining, and bone marrow cells all divide quickly, so they get caught in the crossfire. Every chemotherapy drug, no matter its specific mechanism, produces the same end result in sensitive cells: programmed cell death.
Targeted therapy takes a different approach. Instead of attacking all dividing cells, it interferes with specific key molecules that cancer cells rely on to grow and survive. These molecules are often proteins produced by mutated genes, or receptors on the cell surface that are overactive or overabundant in a tumor. Because normal cells typically don’t share these exact abnormalities, targeted drugs can slow or stop cancer growth while causing less collateral damage to healthy tissue.
The Two Main Types of Targeted Drugs
Targeted therapies fall into two broad categories: small-molecule drugs and monoclonal antibodies. The distinction matters because it affects how the treatment is given and how it works inside your body.
Small-molecule drugs are tiny enough to slip inside cancer cells, where they block enzymes called kinases that drive cell growth. Most of these drugs are taken as daily pills or capsules at home, which makes them more convenient than infusion-based treatments. Kinase inhibitors are classified by exactly how they block the enzyme’s activity and whether that block is temporary or permanent.
Monoclonal antibodies are lab-made proteins designed to latch onto specific targets on the outside of cancer cells. Because they’re large molecules, they typically need to be delivered through an IV infusion at a clinic or as an injection under the skin. Some antibodies work by simply blocking a growth signal from reaching the cell. Others are conjugated, meaning they carry a payload of chemotherapy, a radioactive particle, or a toxin directly to the cancer cell, like a guided missile.
Common Targets in Cancer
Several proteins and gene mutations come up repeatedly across different cancer types. One of the most well-known is HER2, a receptor on the cell surface that drives growth when it’s overexpressed. HER2 is overproduced in roughly 20% of breast cancers, usually because the gene encoding it has been duplicated many times over. Drugs targeting HER2 have transformed outcomes for this group of patients.
EGFR is another frequently targeted receptor. It belongs to the same family as HER2, and mutations in the gene that codes for it are especially common in certain lung cancers. HER2 and EGFR don’t act alone. HER2 is a preferred partner for pairing with other receptors on the cell surface, including EGFR, and this pairing amplifies growth signals. That interconnected signaling network is one reason researchers are exploring drugs that can hit multiple targets at once.
As recently as February 2026, the FDA approved a new kinase inhibitor for adults with advanced non-small cell lung cancer whose tumors carry specific HER2 mutations, illustrating how approvals continue to expand the menu of targeted options for particular genetic profiles.
Biomarker Testing: Matching You to a Drug
Targeted therapy only works if your cancer has the specific molecular feature the drug is designed to attack. That’s why biomarker testing, sometimes called genomic profiling, is a critical first step. A sample of your tumor (from a biopsy or surgery) is analyzed in a lab to look for particular gene mutations, protein levels, or other markers that would make you a candidate for a specific drug.
This process isn’t always straightforward. For lung cancer patients, for example, only about 18% have a tumor sample large enough for complete testing across all recommended genomic markers. When tissue is limited, a liquid biopsy can help. This minimally invasive blood draw detects fragments of tumor DNA circulating in the bloodstream, providing genetic information without another surgical biopsy. Newer multiplex tests can scan for many targetable markers at once from a single sample, which saves tissue and time.
Side Effects of Targeted Therapy
Because targeted drugs are more selective than chemotherapy, they tend to spare many of the tissues that chemo damages. But “more selective” doesn’t mean side-effect free. Each class of drug brings its own set of issues, depending on which molecule it targets.
Skin reactions are among the most common. About 80% of patients taking EGFR inhibitors develop an acne-like rash, sometimes called an acneiform rash because it resembles the deep, cystic acne some teenagers get. It typically appears on the head and neck, chest, and upper back. The lesions can be itchy and painful, especially when they form deeper cysts. While the rash can be uncomfortable and sometimes embarrassing, dermatologists can help manage it with topical treatments and other strategies that keep patients on their cancer therapy.
Other side effects vary by drug class and can include diarrhea, liver enzyme changes, high blood pressure, fatigue, and problems with wound healing. Your care team will monitor for these and adjust treatment if needed.
How Cancer Resists Targeted Therapy
One of the biggest challenges with targeted therapy is that cancers can develop resistance, sometimes within months. The most common way this happens is through new mutations in the very protein the drug targets. These mutations subtly change the protein’s shape so the drug can no longer bind to it effectively. In studies of patients who initially responded to treatment but later relapsed, researchers found new mutations at the time of relapse that weren’t present before treatment began, suggesting the cancer generated these escape routes under the pressure of the drug rather than having them all along.
Cancers have other tricks as well. They can ramp up production of the target protein, overwhelming the drug. They can activate alternative growth pathways that bypass the blocked one entirely, like water finding a new route around a dam. Or they can undergo deeper biological shifts that make them fundamentally less dependent on the original target. Understanding these resistance mechanisms is why many treatment plans now involve combining targeted drugs or sequencing them strategically, hitting the cancer from multiple angles to limit its options for escape.
How Targeted Therapy Is Given
Your experience with targeted therapy depends largely on which type of drug you’re receiving. Small-molecule drugs are most often taken orally, as pills, capsules, or liquids, at home on a daily schedule. This can feel less disruptive than chemotherapy infusions, though it requires consistency and self-monitoring for side effects.
Monoclonal antibodies and some other targeted drugs are given as IV infusions in a clinic or hospital, typically over a period ranging from 30 minutes to several hours depending on the drug. Some newer formulations are available as subcutaneous injections, similar to an insulin shot, delivered into the fatty tissue just under the skin. These tend to be faster than full IV infusions and are sometimes an option after an initial infusion goes smoothly.
Targeted therapy is often used alongside other treatments. It may be combined with chemotherapy, radiation, immunotherapy, or other targeted drugs. In some cases it’s the first-line treatment; in others, it’s used after chemotherapy stops working or when a tumor recurs with a specific genetic profile that makes it a good match.