Trastuzumab Deruxtecan (Enhertu): — What It Is, Who It Suits and What to Expect

Hair thinning and hair loss are among the more common effects of trastuzumab deruxtecan. This happens because the chemotherapy payload affects rapidly dividing cells throughout the body, not only cancer cells. Hair typically begins to thin within the first few weeks of treatment. For most people, hair loss is reversible once treatment ends. Ask your team whether scalp cooling is available at your centre if this is a concern for you.

The most serious known side effect is interstitial lung disease — inflammation of the lung tissue — which can range from mild to life-threatening and requires prompt reporting. Nausea is very common and is managed with anti-nausea medicines your team will prescribe. Low blood counts, particularly low neutrophils, increase infection risk and are monitored by blood tests. Fatigue is common. The heart muscle can occasionally be affected, which is why your team may check your heart function before and during treatment.

ASCO and NCCN guidance identifies interstitial lung disease as a serious risk requiring active monitoring throughout treatment. It can occur at any point — including during the first cycles or much later. Symptoms are a new or worsening cough, shortness of breath, chest tightness, or fever. Do not manage these at home or wait until your next appointment. Call your team or go to hospital the same day. If ILD is confirmed, your oncologist will pause or stop treatment depending on severity.

There is no fixed number of cycles set in advance. Treatment continues for as long as it is working and the side effects are manageable. Your team assesses your response — typically with scans every two to three months — and that result, alongside how you are tolerating the drug, guides whether to continue. If the cancer stops responding, or side effects become unacceptable, your oncologist will discuss what the next step is. Ask them what signs would trigger a review of the decision to continue.

They share the same antibody — trastuzumab — but they are different drugs. Trastuzumab (Herceptin) is the antibody alone. Trastuzumab deruxtecan adds a chemotherapy payload attached by a linker, which is what makes it an antibody-drug conjugate. The side effect profiles differ because of that chemotherapy component, and interstitial lung disease — not a recognised feature of trastuzumab alone — is a known risk with trastuzumab deruxtecan. Previous experience with trastuzumab does not predict your response or tolerability with this drug.

Trastuzumab deruxtecan is given as day-care treatment at CION centres — you do not need to be admitted overnight for your infusion. Response-assessment scans such as PET-CT are coordinated with partner imaging centres. Your oncologist will review your biomarker results, confirm your HER2 status from your biopsy report, and discuss whether this treatment is appropriate for your cancer and stage. The drug itself is dispensed through the hospital pharmacy — CION does not supply or stock it directly.