Medical Oncologist
Osimertinib (Tagrisso)
How Long Does Osimertinib — Take to Work?
Osimertinib starts acting on EGFR-mutant cancer cells from the first dose, but a visible effect on a scan takes longer. Knowing what to expect week by week helps you understand what your body is going through.
Medically reviewed by Dr. T. Raghavender Reddy, Medical Oncologist, MBBS · DM (Medical Oncology) · MD (Radiation Oncology) · Last reviewed August 2026
- Some symptoms ease within weeks — Breathlessness or discomfort related to the tumour can begin to improve before the first scan.
- The first scan is usually at six to eight weeks — This is when your oncologist can see whether the drug is controlling the cancer.
- Stable disease is also a result — If the cancer is not growing, osimertinib is working — shrinkage is not the only measure.
- Response can deepen over months — Some tumours continue to shrink over the first several months, not just at the first scan.
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Osimertinib begins working from the first dose, but it takes time for the effect to become visible. Some people notice symptom changes within the first two to four weeks. The first scan to confirm whether the drug is controlling the cancer is usually done six to eight weeks after you start.
What is happening inside your body in the first weeks?
Osimertinib blocks a faulty protein called EGFR that drives cancer cell growth. It does this from the first dose, but cancer cells do not disappear immediately — they stop dividing and then gradually die.
In the first one to two weeks, you may notice nothing at all. The drug is reaching a steady level in your blood and beginning to act on the tumour, but this is not yet visible on a scan or necessarily felt as a symptom change.
By weeks two to four, some people begin to notice that a symptom related to the tumour — breathlessness, a cough, or discomfort — is slightly easier. This is not guaranteed, and its absence does not mean the drug is not working.
How can you tell osimertinib may be working before your first scan?
- Breathing feels a little easier than it did in the first week
- A tumour-related cough has reduced in frequency or intensity
- Pain or discomfort linked to the tumour has lessened
- Energy levels have started to return
- Swelling from a pleural effusion has reduced
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Dr. C. Raghavendra Reddy
MBBS(Gold Medal), DNB(General Medicine), DM(Medical Oncology)(Gold Medal)
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Dr. Bharati Devi Gorantla
MBBS, MD(General Medicine), DM(Medical Oncology)(Adyar,Chennai), ECMO, MRCP SCE(UK)
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Dr. Owais Mohammed
MBBS, MD (General Medicine), DrNB (Medical Oncology), ECMO, MRCP SCE (Medical Oncology) (UK)
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Dr. Muralidhar Muddusetty
MBBS (AIIMS), MS (Surgery) (AIIMS), DNB (Surgical Oncology), MRCS (Edinburgh)
Surgical Oncologist
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Dr. Vinay Mamidala
MBBS, MS(General Surgery), M.Ch(Surgical Oncology), FMAS, FARIS(Ongoing)
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Dr. Mohammed Imran
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Dr. Vajja Sandeep Kumar
MBBS, MS (General Surgery), DrNB (Surgical Oncology), FALS Oncology
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What does your first scan at six to eight weeks tell you?
The first CT scan after starting osimertinib is usually at six to eight weeks. Your oncologist looks at whether the tumour has shrunk, stayed the same size, or grown.
NCCN and ESMO guidance uses standardised criteria — called RECIST — to describe what the scan shows. A partial response means the tumour has shrunk. Stable disease means it has not grown significantly. Either of these means the drug is doing its job.
If the scan shows a response, it does not mean the drug has done all it will do. Some tumours continue to shrink over the following months. Your oncologist will keep tracking this at each scan.
What if you feel no different after the first few weeks?
Feeling no different does not mean the drug is not working. Many people on osimertinib have no obvious symptoms from the cancer itself, so there is nothing to feel improve.
Imaging — not how you feel — is the primary way to assess response. A scan at six to eight weeks gives a clearer picture than any symptom change.
What is worth reporting at any point is a new symptom, or a side effect that is affecting your daily life. That is a conversation for your team now, not only at your scheduled visit.
What do the words on your scan report mean?
- Partial response
- The tumour has shrunk by a meaningful amount on imaging. This is a positive result. It does not mean the cancer is gone.
- Complete response
- No tumour is visible on imaging. This is uncommon with osimertinib used alone, and does not mean the cancer is cured.
- Stable disease
- The tumour has not grown significantly and has not shrunk enough to count as a partial response. The cancer is being controlled. This is a good result.
- Progression
- The cancer has grown or spread beyond a defined threshold. This triggers a conversation about whether to continue, adjust, or change treatment.
- RECIST
- The standardised criteria oncologists use worldwide to measure tumour response on imaging. It gives a consistent language for comparing scans over time.
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Drug Deep Dive: Gefitinib (Iressa)
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- Gefitinib (Iressa, Geftinat, Geftib): The Complete Patient Guide
- Gefitinib Myths: 'It's Only for Poor Patients' and Other Half-Truths
- Gefitinib Plus Chemotherapy: Does Adding Chemo Actually Help?
- Gefitinib Price in India: Brand, Generic and Monthly Cost
- Gefitinib Rash: Why It Appears in Week Two and How to Treat It
- Gefitinib Side Effects: The Complete List and Timeline
- Gefitinib Success Rate and Survival: An Honest Look at the Numbers
- Gefitinib and Antacids: The Interaction That Silently Reduces Absorption
- Gefitinib in Early-Stage vs Advanced Lung Cancer: Different Goals
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- Tests and Monitoring While You Are on Gefitinib
- When Gefitinib Stops Working: Resistance and What Comes Next
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Common questions
Frequently asked questions
How long before osimertinib shrinks a tumour?
Shrinkage, where it happens, is usually first visible on the scan at six to eight weeks. It can continue beyond that — some tumours keep reducing in size over several months. Not all tumours shrink; stable disease, where the cancer stops growing, is also a meaningful response and is the goal in many cases. Your oncologist will tell you at each scan whether the response is continuing.
Can you feel osimertinib working?
Some people notice tumour-related symptoms easing within the first two to four weeks — a cough becoming lighter, breathing becoming easier, discomfort reducing. Others feel no different at all, and this is not a warning sign. The drug acts at the cellular level, and what you feel depends largely on whether the tumour was causing symptoms you could notice in the first place. Imaging gives a more reliable picture than symptoms alone.
What does stable disease mean — is it good or bad?
Stable disease is a good result. It means osimertinib is preventing the cancer from growing or spreading, which is exactly what it is designed to do. NCCN and ESMO guidelines treat stable disease as a positive outcome because stopping growth has the same practical aim as causing shrinkage: giving you more time with a good quality of life. Your oncologist will explain whether stable disease is the expected goal for your specific situation.
How long does osimertinib keep working?
We do not yet know exactly how long it will work for any individual — the range varies widely. Data reported by ASCO and ESMO show that for many patients with EGFR-mutant lung cancer, osimertinib controls the disease for longer than earlier-generation EGFR inhibitors. Your team monitors this at each scan. It is worth asking now what the plan is for the point when the drug eventually stops working, so that conversation is not a surprise.
What happens at the first scan appointment?
You will have a CT scan, usually of the chest, abdomen and pelvis. Your oncologist reviews it against your starting scan and uses RECIST criteria to classify the result. You will be told whether the result is a partial response, stable disease, or progression, and what it means for continuing treatment. It is reasonable to ask for the report in writing so you can review it after the appointment, when it is easier to take in.
Does it matter what time of day you take osimertinib?
Consistency matters more than the specific time. Taking osimertinib at roughly the same time each day keeps the level in your blood steady. It can be taken with or without food. If you miss a dose, ask your oncology nurse or pharmacist whether to take it or skip it until the next day — do not take two doses to make up for a missed one.