How Long Does Targeted Therapy — Take to Start Working?

Scans — usually CT or PET-CT — are the main way to measure response. Your team will also monitor tumour markers in your blood, which some cancers release and which can change before imaging shows visible shrinkage. Your symptoms matter too: if you are breathing more easily, in less pain, or more energetic, your team weighs that alongside the scan results. Your oncologist will explain which measurements are most meaningful for your specific cancer type.

The timing depends on your cancer type, the drug you are on, and how you are tolerating it — there is no single timeline that applies to everyone. Your team will tell you when your scan is planned. If you have not been told, ask at your next appointment. You are entitled to know what you are waiting for and when the review is expected.

Yes, and it is fairly common. Targeted therapy can reduce cancer activity quickly, which may ease symptoms before the tumour has shrunk enough to be measurable on a scan. Your team will note symptom improvement alongside imaging results when reviewing your response. Telling your oncologist how you feel in the weeks after starting treatment is useful clinical information, not just a personal update.

Not necessarily. Stable disease — where the tumour has not grown — is a meaningful result in targeted therapy. Some cancers are managed for extended periods by keeping disease stable rather than shrinking it. Your oncologist will tell you at the start what the expected goal is for your treatment, so you know in advance how to interpret your scan results. If you are unsure what your result means, ask them to explain it directly.

Treatment usually continues for as long as it is working and you are tolerating it reasonably well. Unlike some chemotherapy regimens, there is no fixed number of cycles that applies across all targeted drugs and cancers. Some people are on targeted therapy for months; others for considerably longer. Your team will review this at each assessment and explain what they are watching for at each stage.

Feeling worse in the early weeks is not automatically a sign the treatment is failing. Some side effects are at their worst shortly after starting and settle as your body adjusts. However, new or worsening symptoms should always be reported — do not wait to see whether something resolves on its own. Tell your team what you are experiencing so they can decide whether it needs management or whether your treatment plan needs reviewing.

Yes, and this is a known part of how many targeted therapies behave over time. Cancer cells can develop new molecular changes that allow them to bypass the blocked pathway — a process called acquired resistance. When this happens, your team will assess whether a different targeted drug, a switch to another treatment approach, or a clinical trial is appropriate. This is an expected step in managing your cancer, and options are usually available when it occurs.

Your oncologist will review what options are available based on how your cancer has changed and what treatments you have already had. This may include a different targeted therapy, chemotherapy, immunotherapy, or enrolment in a clinical trial. A repeat biopsy or further molecular testing is sometimes recommended to understand how the cancer has changed, which helps guide the choice of next treatment. Ask your oncologist to walk you through the options specific to your situation.