Can cancer become resistant to targeted therapy?

Yes. Cancer cells can become resistant to targeted therapy.

Resistance can happen in two main ways. Sometimes the target itself changes, so the targeted therapy can no longer interact with it. Other times, the cancer cells find new ways to grow that do not depend on the target at all.

Why this happens to almost every targeted drug eventually

A tumor is not one cell copied over and over. It is a population of cells that keep dividing, and dividing cells make copying mistakes. So a tumor holds many slightly different versions of itself.

A targeted drug kills the cells that depend on the target it blocks. That clears out the crowd. But any cell that happens to carry a change letting it survive now has the space to itself, with no competition. Its descendants take over.

That is evolution, running inside a person over months. It is not a sign that anyone did anything wrong, and it is not a sign that you took the drug incorrectly.

Targeted therapy is especially exposed to this because of what makes it good. These drugs work by blocking one specific switch a cancer depends on. That precision is why they often cause fewer side effects than chemotherapy. It is also why a single change to that switch can shut the whole drug down.

The second route is different and sometimes harder to see coming. The target stays blocked, but the cell reroutes around it, like traffic finding another street. The drug still works exactly as designed. The cancer has simply stopped needing what it blocks.

What it looks like, and what happens next

Resistance usually shows up as a drug that worked well and then stops. Scans that had been stable start showing growth. Markers that had fallen begin to rise.

This is one reason your care team watches how the treatment is working over time, using exams, blood tests, and scans. The point of that schedule is to catch a change early enough to act on it.

Resistance often has a next move. In non-small cell lung cancer with an abnormal EGFR gene, osimertinib is approved by name for cancer that spread and then got worse during or after treatment with another EGFR tyrosine kinase inhibitor. In other words, a drug built for the resistant version of the disease already exists. Similar second and third options exist across several targets.

Because of resistance, targeted therapy may work best when it is used with more than one type of targeted therapy or combined with other cancer treatments, such as chemotherapy and radiation. Hitting two points at once makes it harder for any single change to rescue the cell.

What to ask if your drug stops working

Since NCI describes the target itself as something that can change, the tumor growing now may not match the tumor that was tested at the start. Ask whether repeat biomarker testing is worth doing, and whether that would need a new biopsy or could be done from blood.

Ask what specifically is growing, and whether it is one spot or many. Ask whether a next-generation drug exists for your target, and whether a clinical trial is open for your situation.

If a targeted therapy stops working, they can talk with you about other options. Progression on one drug is a turn in the road, not the end of it.