Trastuzumab and Trastuzumab Deruxtecan in Breast Cancer

Neither is immunotherapy in the checkpoint-inhibitor sense. Trastuzumab is a HER2-targeted monoclonal antibody. Part of how it works is by flagging HER2-positive cells for the patient’s own immune cells to destroy, which is why India often files it under immunotherapy. Trastuzumab deruxtecan is an antibody-drug conjugate — a similar antibody carrying a chemotherapy payload.

This is the single most useful thing to settle first, because the word is used three different ways in an Indian hospital corridor. A monoclonal antibody points the immune system at a specific target on the tumour. A checkpoint inhibitor releases a brake on T cells that already recognise the tumour. An antibody-drug conjugate uses the antibody as a delivery vehicle, so chemotherapy is released mainly inside cells carrying the target protein.

Trastuzumab belongs in the first group and has done since it entered Indian practice in the early 2000s. That is the part patients are rarely told: a treatment a mother or an aunt may have had a decade ago is described today, quite reasonably, as an immune-directed therapy. Trastuzumab deruxtecan belongs in the third group. Pembrolizumab and nivolumab belong in the second.

Only patients whose tumour expresses HER2 — and, for trastuzumab deruxtecan in some settings, HER2-low or HER2-ultralow disease. HER2 status comes from immunohistochemistry, confirmed where needed by in-situ hybridisation. In India, HER2-positive disease is estimated at roughly 12 to 19 per cent of breast cancers. The pathology report decides eligibility, long before cost does.

Trastuzumab is approved for HER2-positive breast cancer, in both early and metastatic settings, and for HER2-positive gastric and gastro-oesophageal cancer. It is on the World Health Organization’s Model List of Essential Medicines and on India’s National List of Essential Medicines. In HER2-negative disease it does nothing at all, and no price makes it appropriate.

Trastuzumab deruxtecan reached India much later, and its approvals are setting-specific rather than general. AstraZeneca Pharma India received permission from the Drug Controller General of India to import and market it in May 2023 and launched it here in January 2024. CDSCO has approved further indications since, each announced publicly.

Where the evidence for the tumour-agnostic indication came from: the October 2025 CDSCO approval announcement cited three multicentre studies in 192 previously treated patients, reporting confirmed objective response rates of 51.4 per cent, 52.9 per cent and 46.9 per cent across the three. Those are response rates in selected trial populations, not a prediction for any individual, and they say nothing about how long a response lasts.

Reported Indian coverage in July 2026 put it at around ₹1.6 lakh per 100 mg vial — indicative, as of August 2026. A vial price is not a cycle price. At the labelled breast-cancer dose of 5.4 mg per kg every three weeks, an adult of around 60 kg needs roughly four vials a cycle. Plain trastuzumab sits at a completely different level.

The honest limit of any total. In the metastatic setting, trastuzumab deruxtecan is given until the disease progresses or the side effects become unacceptable — not for a fixed number of cycles. A total course figure therefore cannot be stated in advance by anyone, and a quoted total should be read as an assumption about duration rather than as a fact. Adjuvant trastuzumab is the opposite case: a planned course, usually around 17 to 18 three-weekly cycles, which can be costed in advance.

Three questions that move the number more than the brand does. How many cycles are planned, or on what basis treatment will be reviewed if the number is open-ended. What dose body weight gives, since that decides the vial count. And whether the estimate separates the drug from day-care, monitoring and consultation charges — an itemised estimate makes every other question answerable.

Most people with breast cancer are candidates for neither medicine, and no price changes that. Both act only where the tumour expresses HER2, and trastuzumab deruxtecan is approved for defined settings rather than as a general option. Eligibility is decided by a pathology report and a treatment plan, not by a budget.

• Not for HER2-negative cancer. If the report reads IHC 0 or 1+, or IHC 2+ with a negative in-situ hybridisation test, plain trastuzumab has no role at any price. HER2-low is a separate category and is not an indication for trastuzumab itself.
• Not a general-purpose upgrade. Trastuzumab deruxtecan is approved in India for specific settings, several of them only after a prior anti-HER2 regimen. Being HER2-positive does not by itself place a patient in one of those settings.
• Not where heart pumping function is already significantly reduced, without cardiology input. Both medicines can lower the ejection fraction. An echocardiogram or MUGA scan is done before starting and repeated during treatment, and a low baseline reading can mean treatment is deferred, monitored more closely, or not used.
• Not straightforward where significant lung disease already exists. Trastuzumab deruxtecan carries a recognised risk of interstitial lung disease, sometimes serious. Pre-existing lung disease changes the risk calculation, and that is a matter for the treating team rather than for a web page.
• Not in pregnancy. Both can harm a developing baby. Effective contraception is advised during treatment and for a period afterwards; the interval is set by the treating team.
• Not a substitute for the rest of the plan. Both are given alongside surgery, chemotherapy or radiotherapy where those are indicated, never instead of them. Choosing one in place of a recommended treatment is not a cost saving.

The two are also not interchangeable with each other. A trastuzumab biosimilar is not a lower-cost trastuzumab deruxtecan, and trastuzumab emtansine is a third, separate antibody-drug conjugate again. Which of the three a prescription actually names is worth confirming in writing before any cost planning begins.

Patent position and competition, not clinical worth. Trastuzumab lost exclusivity in India more than a decade ago, and several approved similar biologics now compete on price. It also sits on the National List of Essential Medicines, so NPPA notifies a ceiling price that every brand must respect. Trastuzumab deruxtecan is a patented import with one supplier and no notified ceiling.

India’s trastuzumab market is the closest thing the country has to a completed biosimilar case study. The first Indian similar biologics arrived in 2014 at a modest discount. The steep fall came about five years later, once several suppliers were competing and price control had been applied. Trastuzumab Biosimilars in India sets out that price arc in full, including which brands are sold here and what comparability means when a regulator approves a similar biologic.

None of that has happened for trastuzumab deruxtecan, and none of it is close. It is a patented molecule, imported rather than made here, with a single company marketing it and no similar biologic in sight. Antibody-drug conjugates are also genuinely harder and costlier to manufacture than a plain antibody, because the payload and the chemical linker have to be produced and attached to a consistent standard. Waiting for a price fall is not a plan: delaying treatment to chase a future price is a clinical decision with clinical consequences.

The same pattern separates the rest of this class. Which Antibody Medicines Are Available in India? maps which antibodies are marketed here and where each sits on the patent-and-competition curve, and Immunotherapy Medicines Explained is the index of individual molecules and their Indian cost picture.

Heart function for both, and lungs for trastuzumab deruxtecan. Both antibodies can reduce the heart’s pumping function, so an echocardiogram or MUGA scan is done before starting and at intervals during treatment. Trastuzumab deruxtecan carries an additional recognised risk of interstitial lung disease, which is why a new cough or breathlessness is treated as urgent.

One point that should not be softened. A new cough, new breathlessness or a fever while on trastuzumab deruxtecan is not something to manage at home, and not something to raise at the next cycle. Interstitial lung disease is a recognised and potentially serious effect of this medicine. Anyone with those symptoms should go to the hospital treating them the same day, and should say which medicine they are on when they arrive.

Both medicines are given as day-care infusions, so a treatment day does not usually require admission. Antibody-drug conjugates as a group share this monitoring pattern rather than the checkpoint-inhibitor one — Brentuximab Vedotin: Uses, Cost and Side Effects covers the equivalent picture for the antibody-drug conjugate used in Hodgkin lymphoma, and Cetuximab and Nimotuzumab in Head and Neck Cancer covers two plain antibodies whose Indian price story is different again.

• Which Antibody Medicines Are Available in India? — the marketed list, and where each molecule sits on the patent curve.
• Brentuximab Vedotin: Uses, Cost and Side Effects — another antibody-drug conjugate, in a blood cancer rather than breast cancer.
• Cetuximab and Nimotuzumab in Head and Neck Cancer — two targeted antibodies, one imported and one made in India.
• Trastuzumab Biosimilars in India — the full price arc behind the cheaper half of this page.
• Immunotherapy Medicines Explained — the index of checkpoint inhibitors, antibodies and molecule-by-molecule cost pages.
• Immunotherapy at CION — what this class of treatment does, who it suits, and who it does not.

Editorial information about two named medicines — not an offer, a price list, or a recommendation to use either, and no comparative quality claim between manufacturers. All pricing, regulatory and dosing statements are indicative and dated to August 2026, drawn from published manufacturer and CDSCO approval announcements, NPPA ceiling-price notifications, approved product information and reported Indian coverage. Whether trastuzumab or trastuzumab deruxtecan applies to a particular cancer is a decision for the treating oncologist, on the basis of a HER2 test result and the full clinical picture.