Enhertu Myths: — What the Evidence Actually Shows

Enhertu is just a stronger version of Herceptin.

Both drugs use the same antibody component — trastuzumab — and both target HER2, which is why the confusion is understandable. But Herceptin is a bare antibody: it attaches to HER2 and blocks growth signals from outside the cell. Enhertu is an antibody-drug conjugate: the antibody carries a chemotherapy payload into the cell and releases it there. Different mechanism, different side effect profile, and used in different clinical situations. They share a name fragment, not a mechanism.

If Herceptin stopped working, Enhertu will not work either.

Because both drugs target HER2, it seems logical that resistance to one would mean resistance to both. But NCCN and ASCO guidance specifically places Enhertu in the setting of prior trastuzumab-based therapy, because the mechanism that drives response is different. Herceptin's antibody blocks a growth signal from outside the cell. Enhertu's payload disrupts cell replication from inside it, and the drug also affects neighbouring tumour cells through a bystander effect. Prior Herceptin treatment does not close the door on Enhertu.

You need to be HER2-positive to be eligible for Enhertu.

That was true for Herceptin, and for many years patients with lower HER2 levels had no access to any HER2-targeted therapy. That changed when the FDA approved Enhertu for HER2-low breast cancer — a category where the cancer has some HER2 on its surface, but not enough to be called positive under older criteria. If you were told you were HER2-negative some years ago, it is worth asking your oncologist to look at your exact score under current reporting standards. The answer may be different from your original diagnosis.

The side effects are the same as standard chemotherapy.

Enhertu does share some side effects with chemotherapy — nausea, hair thinning, and fatigue are all possible. People assume the overlap is complete because Enhertu contains a chemotherapy payload. But it carries a specific risk that standard chemotherapy does not: interstitial lung disease, an inflammation of the lung tissue that requires its own monitoring plan. Any new breathlessness, dry cough, or change in your exercise tolerance while on Enhertu is a symptom to report the same day, not at your next scheduled visit.

It is unaffordable, so there is no point asking about it.

Cost estimates that circulate online — often based on pricing in the US or UK market — lead families to conclude without asking that Enhertu is simply not an option. Any cost figure is indicative and dated, and what you actually pay may differ significantly through manufacturer support programmes, clinical trial access, or insurance coverage. Speak to your hospital's financial counselling team before drawing a conclusion based on a number you found online. The conversation costs nothing and the answer may surprise you.