her2

Spanish breast oncologist leading DESTINY-Breast09, which moved trastuzumab deruxtecan into first-line HER2-positive disease.

Led PERSEPHONE, which showed six months of trastuzumab is nearly as good as twelve for most patients.

A HER2 mutation is a change in the gene's kinase domain, most often an exon 20 insertion, found in about 2 to 3 percent of lung adenocarcinomas. It is a different thing from HER2 amplification or overexpression, and it selects trastuzumab deruxtecan and, since 2025, zongertinib in lung cancer.

IHC 0 is no HER2 staining, or faint staining in 10 percent or fewer cells. It is HER2-negative, but the label now separates true zero from 'IHC 0 with membrane staining', the ultralow group that trastuzumab deruxtecan can treat in hormone-receptor-positive breast cancer.

IHC 1+ is faint, incomplete HER2 staining. It was called HER2-negative for twenty years; since 2022 it is the larger half of HER2-low, which trastuzumab deruxtecan treats in breast cancer.

IHC 2+ is the in-between HER2 result: moderate staining that cannot be called positive or negative by eye, so the laboratory runs an ISH gene test. 2+ with amplification is HER2-positive; 2+ without it is HER2-low.

IHC 3+ means strong, complete membrane staining for HER2 in more than 10 percent of tumour cells. It is HER2-positive without needing a gene test and is the gate for trastuzumab, its combinations and antibody-drug conjugates in breast, stomach, biliary and, since 2024, any solid tumour.

ISH counts copies of the HER2 gene in each tumour cell. A ratio of 2 or more against the chromosome 17 control, or 6 or more copies per cell, is amplified and HER2-positive whatever the protein stain showed.

HER2-low is not a new stain but a new reading of the old one: 1+ or 2+ without gene amplification. It covers about half of breast cancers and makes them eligible for trastuzumab deruxtecan.

HER2-ultralow is an IHC 0 result with a trace of membrane staining in a few cells. Since 2025, in hormone-receptor-positive breast cancer that has stopped responding to hormone therapy, it is enough for trastuzumab deruxtecan.

Breast oncologist who took T-DM1 and then trastuzumab deruxtecan from first-in-human studies to approval.

Led CLEOPATRA, which showed dual HER2 blockade with pertuzumab gives an unprecedented 16-month survival gain in metastatic disease.