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Tumours with a little HER2 (IHC 1+ or 2+ without amplification), or a trace (ultralow), which older HER2 drugs ignored but Enhertu can attack.
HER2-low describes tumours with a little HER2, scored IHC 1+ or 2+ without gene amplification, and HER2-ultralow describes a trace, scored IHC 0 with faint membrane staining in a small fraction of cells. Older HER2 drugs ignored these tumours, but Trastuzumab deruxtecan can attack them, as DESTINY-Breast04 and DESTINY-Breast06 showed in HR-positive / HER2-negative breast cancer and Triple-negative breast cancer (TNBC). The result redefined what 'HER2-negative' means and put pressure on pathology to score the low end reliably, hence the links to Histopathology & immunohistochemistry, Companion diagnostics, the pairing HER2-low scoring to T-DXd and the idea on AI quantification of HER2-low. It also appears in the bottleneck on biomarker validation and the Giuseppe Curigliano entry.
Ball-and-stick model from PubChem 2D record (no 3D conformer available). PubChem record
Showing the molecule this term concerns: Trastuzumab deruxtecan.
The glossary entry explains the word; the readout page carries the scoring rule, the thresholds approvals use, the companion diagnostics and the tests.
Three-quarters of chemotherapy-naive TNBC would be low or ultralow by the DESTINY-Breast06 definitions, but ultralow is unlabelled in TNBC and carries no prognostic weight.
Patients with hormone-receptor-positive metastatic breast cancer that has stopped responding to endocrine therapy can be offered trastuzumab deruxtecan as their first chemotherapy-type treatment if the tumour shows any HER2 staining, rather than waiting until after conventional chemotherapy. Whether to use it before or after chemotherapy is now a choice, since overall survival was not shown to differ and the drug carries a risk of lung inflammation.
Patients whose breast cancer was previously called HER2-negative may now be eligible for an effective HER2-directed drug if their tumour has even low-level HER2 staining, so pathology reports must now distinguish HER2-low (1+ or 2+/ISH-negative) from HER2-zero. This applies to metastatic disease after at least one line of chemotherapy; it does not mean these patients benefit from trastuzumab or other older HER2 drugs.
The trial-grade HER2-low share for TNBC is about a third, and the survival difference hints that HER2-zero triple-negative disease is the more aggressive group.
HER2-low is a drug eligibility label, not a biological subtype, in triple-negative disease; because a third of patients qualify for trastuzumab deruxtecan on a score pathologists disagree about, re-scoring and digital assistance for HER2 0 versus 1+ is a practical gap.
Shares Breast cancer (all types), Triple-negative breast cancer (TNBC), HR-positive / HER2-negative breast cancer and the tag precision.
Shares Breast cancer (all types), Triple-negative breast cancer (TNBC), HR-positive / HER2-negative breast cancer and the tag precision.
Shares Companion diagnostics, Histopathology & immunohistochemistry, Triple-negative breast cancer (TNBC) and the tag precision.
Shares Companion diagnostics, Breast cancer (all types) and the tag precision.
Shares Companion diagnostics, Triple-negative breast cancer (TNBC) and the tag precision.
Shares Breast cancer (all types), Triple-negative breast cancer (TNBC) and the tag precision.
Shares Breast cancer (all types) and the tag precision.
Shares Breast cancer (all types), Triple-negative breast cancer (TNBC), HR-positive / HER2-negative breast cancer and the tag precision.
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