Targeted therapy

Targeted therapy blocks specific changes inside cancer cells, which is why biomarker testing matters.

Rosa: Hi, I'm Rosa. Targeted therapy goes after specific changes inside cancer cells. Let me explain how it works, and why testing your tumor matters.

Targeted therapy is a group of medicines that go after specific changes in cancer cells. These changes might be in genes, called mutations, or in proteins on the surface of the cell. Examples include drugs for EGFR, ALK, or KRAS changes in lung cancer, HER2 in breast and stomach cancer, and BRAF in melanoma.

Cancer cells often grow because a switch inside them is stuck in the on position. A targeted drug works like a key made for one lock. It fits a specific part of the cancer cell and turns off the signal that tells it to grow. Because the target is specific, these drugs usually work only if your cancer has that change.

That is why biomarker testing, also called tumor or molecular testing, is so important. A sample from a biopsy or a blood test is checked for changes that a targeted drug can treat. Ask your care team whether your cancer has been tested and what the results mean.

Many targeted drugs are pills taken at home every day. Others are given through a vein or as a shot. Treatment often continues for as long as it keeps the cancer under control and side effects are manageable. Some targeted drugs are used for a set time after surgery to lower the chance the cancer comes back.

Side effects depend on the drug. Common ones include rash or acne-like skin changes, dry skin, nail problems, diarrhea, tiredness, mouth sores, high blood pressure, and changes in liver tests. Skin side effects are common with EGFR drugs and can often be prevented or eased with skin care and prescribed creams or antibiotics. Over time, cancer cells can find a way around the drug. If that happens, your team may test again and change treatment.

Call your care team right away for new or worse cough or shortness of breath, chest pain, fast or irregular heartbeat, severe diarrhea, yellow skin or eyes, a rash that blisters or peels, severe headache, or vision changes. If it feels very bad, call 911.

Taking pills at home

Take your medicine at the same time each day and exactly as directed. Ask whether to take it with or without food, and what to do if you miss a dose. Do not stop or change doses without talking to your team.

Drug interactions

Some targeted pills interact with heartburn medicines, grapefruit, St. John's wort, antibiotics, and other drugs. Ask your pharmacist to check every medicine and supplement you take.

Skin care

Use gentle, fragrance-free soap and a thick moisturizer every day. Wear sunscreen and protective clothing. Tell your team early about rash or sore, red skin around the nails.

Cost and pharmacy

Many targeted pills come from a specialty pharmacy and can be expensive. Ask a financial counselor about copay help before you start.

Questions to ask

What target does this drug block? Was my tumor tested for all the important changes? How will we know if it is working? What happens if the cancer stops responding?

Myth: Pills are weaker than IV treatment

Fact: Many targeted pills are among the most effective treatments for cancers with the right change. A pill is not a lesser treatment.

Myth: Targeted therapy has no side effects

Fact: Targeted drugs are often easier than chemo, but they still have side effects. Most can be managed if you tell your team early.

Last updated: 2026-10-27. Medically reviewed by Veli Bakalov, MD, medical oncologist (October 2026). General education from Step by Step, the patient portal of HemeOncBuddy.