Enhertu in Breast, Gastric and Lung Cancer: — One Drug, Three Diseases

No — they are different drugs that both target HER2, but they work differently. Herceptin (trastuzumab) is an antibody that targets HER2 on its own. Enhertu uses the same antibody but attaches a chemotherapy payload to it, delivered directly into the cancer cell when the antibody locks on. Enhertu is typically given after trastuzumab-based treatment has already been tried, not instead of it or at the start of treatment.

Not automatically. In HER2-positive breast cancer, Enhertu is generally considered after one or more prior HER2-targeted treatments have stopped working — not as the first option. In early-stage disease, the specific situation where it is discussed is narrower still. Your oncologist will explain the recommended sequence of treatments for your situation and where Enhertu fits, if it is indicated for you at all.

HER2-low breast cancer describes tumours where HER2 is present at low levels — detectable by testing, but below the threshold previously used to define HER2-positive disease. For many years this group was not considered candidates for HER2-targeted treatment. Enhertu has shown activity in HER2-low metastatic breast cancer, and both ASCO and the FDA now recognise HER2-low as a group for whom it can be considered. Your pathology report will state whether your cancer falls into this category.

In lung cancer, what qualifies for Enhertu is a mutation in the HER2 gene — a specific change in the genetic code. This is different from HER2 protein overexpression on the cell surface, which is the finding that matters in breast and gastric cancer. HER2 overexpression alone, without a gene mutation, is not the qualifying marker for lung cancer. Your oncologist or pathologist can confirm exactly what your molecular testing showed and whether a HER2 mutation is present.

The risk specific to Enhertu that your team will monitor most carefully is interstitial lung disease — inflammation of the lung tissue. It can range from mild to serious, and early detection significantly affects how it is managed. Tell your team promptly about any new dry cough, increased breathlessness, or any change in how easily you get short of breath, even if it seems minor. Nausea is common and is usually manageable with medicines prescribed alongside treatment. Heart function is checked throughout.

Enhertu is given as an infusion into a vein, typically once every three weeks, as day care — you do not need to be admitted overnight. The infusion takes a few hours. Your team will tell you how many cycles are planned based on your diagnosis and how you are responding to treatment, and that plan may be reviewed at each assessment.