Medical Oncologist
About Enhertu (Trastuzumab Deruxtecan)
Who Can Take — Trastuzumab Deruxtecan?
Your eligibility for trastuzumab deruxtecan depends on your HER2 test result, not your cancer type alone. The drug is now approved for more patients than it used to be — including a group previously told they were not HER2-eligible.
Medically reviewed by Dr. T. Raghavender Reddy, Medical Oncologist, MBBS · DM (Medical Oncology) · MD (Radiation Oncology) · Last reviewed August 2026
- Biomarker testing decides it — Your IHC score from biopsy tissue — not the cancer type alone — determines whether you qualify.
- HER2-low now qualifies in breast cancer — A landmark approval extended eligibility to patients with lower HER2 expression who were previously excluded.
- Gastric and lung criteria differ — Gastric cancer requires HER2-positive status. Lung cancer eligibility depends on a HER2 mutation, tested differently.
- Being ineligible is not the end of options — An IHC 0 result tells you which treatment fits better, not how serious your situation is overall.
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Trastuzumab deruxtecan is approved for HER2-positive and HER2-low breast cancer, HER2-positive gastric cancer, and HER2-mutant lung cancer. Your HER2 test result from your biopsy tissue decides eligibility. The IHC score and, in some cases, a gene amplification or mutation test are what your oncologist uses to assess whether it fits your cancer.
What determines whether you are eligible?
Trastuzumab deruxtecan targets HER2, a protein on the surface of some cancer cells. How much of that protein your tumour makes — measured by a laboratory test on your biopsy tissue — is the starting point for deciding eligibility.
The scoring system used is called IHC, or immunohistochemistry. A score of IHC 3+, IHC 2+, or IHC 1+ may each lead to eligibility, but which applies to you depends on your cancer type and what treatment you have already received.
For non-small cell lung cancer, eligibility works differently. It depends on a mutation in the HER2 gene found by genetic sequencing — not on how much protein the cells produce.
Which patients are currently approved to receive it?
- Breast cancer — HER2-positive (IHC 3+, or IHC 2+ confirmed by a gene amplification test), after at least one prior HER2-targeted regimen
- Breast cancer — HER2-low (IHC 1+, or IHC 2+ without gene amplification), after prior chemotherapy
- Gastric or gastro-oesophageal junction cancer — HER2-positive, after prior trastuzumab-based treatment
- Non-small cell lung cancer — HER2-mutant on genetic sequencing, after prior platinum-based chemotherapy
- Adequate general fitness for the regimen — your oncologist will assess this before starting
Meet the Specialists
17+ senior cancer specialists. One panel for your case.
Trained at AIIMS, Tata Memorial, and leading international centres. Combined 150+ years of experience. Every complex case is reviewed by 3+ of them — together.
Medical Oncologist
Dr. C. Raghavendra Reddy
MBBS(Gold Medal), DNB(General Medicine), DM(Medical Oncology)(Gold Medal)
Medical Oncologist
Dr. Bharati Devi Gorantla
MBBS, MD(General Medicine), DM(Medical Oncology)(Adyar,Chennai), ECMO, MRCP SCE(UK)
Medical Oncologist
Dr. Owais Mohammed
MBBS, MD (General Medicine), DrNB (Medical Oncology), ECMO, MRCP SCE (Medical Oncology) (UK)
Medical Oncologist
Medical Oncologist
Surgical Oncologist
Dr. Muralidhar Muddusetty
MBBS (AIIMS), MS (Surgery) (AIIMS), DNB (Surgical Oncology), MRCS (Edinburgh)
Surgical Oncologist
Surgical Oncologist
Surgical Oncologist
Dr. Vinay Mamidala
MBBS, MS(General Surgery), M.Ch(Surgical Oncology), FMAS, FARIS(Ongoing)
Surgical Oncologist
Radiation Oncologist
Radiation Oncologist
Radiation Oncologist
Hematologist
Interventional Radiologist
Dr. Mohammed Imran
Surgical Oncologist
Dr. Vajja Sandeep Kumar
MBBS, MS (General Surgery), DrNB (Surgical Oncology), FALS Oncology
Surgical Oncologist
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What the terms on your pathology report mean
- HER2-positive
- Your tumour makes a high amount of HER2 protein, or has extra copies of the HER2 gene. Reported as IHC 3+, or IHC 2+ confirmed by an ISH gene test.
- HER2-low
- Your tumour makes a small amount of HER2 protein — reported as IHC 1+, or IHC 2+ without gene amplification. Trastuzumab deruxtecan is approved for this group in breast cancer.
- HER2-negative (IHC 0)
- No detectable HER2 protein on the cell surface. Trastuzumab deruxtecan has no target here and is not appropriate for this result.
- IHC (immunohistochemistry)
- A laboratory stain applied to your biopsy tissue that shows how much HER2 protein is present. Scored on a scale of 0, 1+, 2+, or 3+.
- ISH (in situ hybridisation)
- A gene test done when IHC comes back as 2+ to check whether the HER2 gene is amplified. Also called FISH or CISH depending on the method used.
- HER2 mutation (lung cancer)
- A change in the DNA sequence of the HER2 gene, found by next-generation sequencing. This is different from IHC scoring and is the relevant marker for lung cancer eligibility.
What does a result that does not qualify mean for you?
An IHC 0 result — HER2-negative — means the drug has no surface target on your cells and is not appropriate. That tells you which treatment fits, not how serious your situation is overall.
Your oncologist will move to the treatment the evidence supports for your specific cancer, which may be chemotherapy, another targeted therapy, hormone therapy, or a combination.
HER2 expression can change over time. If your disease relapses or spreads to a new site, it is worth asking whether HER2 testing on fresh tissue is worth repeating — your result now may not be the same as it was at diagnosis.
Questions families ask after the prescription
My report says IHC 2+. Does that automatically mean I am eligible?
Not on its own. An IHC 2+ result is borderline and needs a second test — ISH, also called FISH or CISH — to check whether the HER2 gene is amplified. If it is amplified, you are classified HER2-positive. If it is not, you are classified HER2-low. Both groups can be eligible for trastuzumab deruxtecan in breast cancer, but through different approval pathways. Ask your oncologist whether the ISH test has already been done on your sample, or whether it still needs to be ordered.
Is trastuzumab deruxtecan the same as Herceptin?
They both target HER2, but they work differently. Herceptin (trastuzumab) is an antibody that attaches to HER2 and blocks a growth signal. Trastuzumab deruxtecan is an antibody-drug conjugate — the same antibody carries a chemotherapy payload directly into HER2-expressing cells and releases it there. The two drugs are related but not interchangeable, and tolerating Herceptin does not predict how your tumour will respond to trastuzumab deruxtecan.
Do I need a new biopsy if my tissue was tested years ago?
Sometimes, yes. HER2 expression can differ between a primary tumour and a site the cancer has since spread to, so a result from several years ago may not describe your current disease. If the original sample was too small for adequate testing, or if the cancer is now active at a different site, your oncologist may recommend a fresh biopsy. Ask specifically whether the HER2 result being used to make the current decision is from your most recent sample.
Can we pay for it privately if our result does not qualify?
Clinical eligibility is not about ability to pay. Trastuzumab deruxtecan carries real risks, including a lung reaction called interstitial lung disease that requires careful monitoring throughout treatment. Those risks are worth taking where the biomarker evidence supports benefit, and are not worth taking where it does not. A responsible oncologist will decline to prescribe it where the tumour biology does not indicate it — that refusal is protecting you, not rationing care. If you want certainty on your result, asking for a second opinion on the biomarker interpretation is entirely reasonable.
What are the most important risks to understand before starting?
The most serious is interstitial lung disease — inflammation in the lung tissue that can range from mild to severe. ASCO and ESMO guidance requires active monitoring for this throughout treatment, and you should tell your team immediately if you develop new shortness of breath or a new cough at any point. Nausea is common and is usually managed with medication before and after each infusion. Fatigue, hair thinning, and low blood counts are also reported. Your team will go through the complete list with you before you agree to start.
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Common questions
Frequently asked questions
What cancers is trastuzumab deruxtecan currently approved for?
It is currently approved for HER2-positive and HER2-low breast cancer, HER2-positive gastric or gastro-oesophageal junction cancer, and HER2-mutant non-small cell lung cancer. Within each group, specific criteria apply — including prior treatment lines. NCCN and ESMO guidance covers all three indications. Your oncologist will confirm which category applies to your diagnosis and whether you meet the full criteria for that indication.
Does the HER2-low approval apply to gastric cancer as well as breast cancer?
Not currently. The HER2-low approval applies to breast cancer. Gastric cancer eligibility still requires HER2-positive status — IHC 3+, or IHC 2+ confirmed by gene amplification testing. If your gastric cancer report shows HER2-low, trastuzumab deruxtecan is not part of the current standard approach for that indication, and your oncologist will explain which options apply to your situation.
How long does HER2 testing take before a decision can be made?
IHC testing is usually done on biopsy tissue you have already had, and results typically take around one to two weeks from when the laboratory receives the sample. An additional ISH test, if needed for a 2+ result, adds a few more days. If a fresh biopsy is required because the original sample was insufficient, the timeline is longer. Ask your team when the sample was sent and when the result is expected, so you are not left without a timeframe.
What happens if I cannot tolerate the drug after starting?
Your oncologist will assess the reason and the severity. Many side effects — including nausea and fatigue — can be managed with medication while treatment continues. More serious reactions, such as lung inflammation, may require treatment to pause or stop. That decision depends on how severe the reaction is and how it responds to initial management. Being unable to continue does not close all options; your oncologist will review what is appropriate next.
Is trastuzumab deruxtecan given as day care or will I need to stay in hospital?
It is given by intravenous infusion, and at CION it is administered as day care — you do not need to be admitted overnight for the infusion itself. The first infusion is usually longer and monitored more carefully. Response-assessment scans such as PET-CT are coordinated with partner imaging centres. Your care team will give you the full schedule of infusions and scans before you begin treatment.
Can my HER2 result change if the cancer spreads to a new site?
Yes, it can. HER2 expression is not always the same at every site of a cancer, and a secondary deposit may show a different score from the primary tumour. This is one reason retesting is sometimes recommended when disease progresses or spreads to a new location. If your eligibility was established from an early biopsy and your situation has since changed, ask your oncologist whether testing the currently active site would give more useful information.