Algeria Key takeaways
- HER2-low = IHC 1+ or IHC 2+/ISH-negative.
- HER2-ultralow refers to IHC 0 with faint, incomplete membrane staining in 10% or fewer tumour cells.
- HER2-low/ultralow should not be equated with HER2-positive disease.
- T-DXd has demonstrated clinically relevant activity in HR-positive metastatic HER2-low/ultralow breast cancer after endocrine therapy.
- For Algeria, accurate and standardized HER2 assessment is becoming increasingly important as therapeutic options expand.
For many years, HER2 testing in breast cancer seemed straightforward: HER2-positive disease could receive HER2-directed therapy, while HER2-negative disease could not.
That distinction is becoming less absolute.
In 2026, HER2-low and HER2-ultralow expression can have therapeutic relevance, particularly in hormone receptor-positive metastatic breast cancer. This is an important development for breast cancer practice in Algeria—but it also raises a very practical question:
Can we reliably identify the patients who may benefit?
What does HER2-low mean?
HER2-low generally refers to tumours with IHC 1+ or IHC 2+ with negative ISH. HER2-ultralow refers to tumours classified as IHC 0 that show faint, incomplete membrane staining in 10% or fewer tumour cells.
These categories are not the same as HER2-positive breast cancer, and they should not be interpreted as new biological subtypes.
Their importance comes from the development of antibody–drug conjugates (ADCs).
In DESTINY-Breast06, trastuzumab deruxtecan improved progression-free survival compared with physician’s-choice chemotherapy in patients with HR-positive, HER2-low metastatic breast cancer who had received prior endocrine therapy and no chemotherapy for advanced or metastatic disease. Exploratory results also showed activity in HER2-ultralow disease.
Why does this matter in Algeria?
The emergence of HER2-low treatment strategies makes the quality of the pathology report increasingly important.
An IHC result of 0, 1+, or 2+ is no longer simply a classification used to determine whether conventional anti-HER2 therapy is indicated.
In selected metastatic patients, the distinction between these categories may have therapeutic implications.
This places greater emphasis on:
- standardized HER2 IHC assessment;
- clear reporting of IHC scores;
- appropriate ISH testing for equivocal cases;
- communication between pathologists and oncologists through the RCP.
For Algerian oncology teams, this is an important practical evolution. The availability of a treatment is only one part of the pathway; the diagnostic information required to identify eligible patients must also be available and reliable.
From HER2 testing to treatment selection
The therapeutic landscape is moving from a simple binary question—
HER2-positive or HER2-negative?
—to a more nuanced one:
What is the level and pattern of HER2 expression, and does it matter for the treatment being considered?
For an Algerian patient with metastatic HR-positive breast cancer, this distinction may become particularly relevant when endocrine-based options have been exhausted or are no longer appropriate.
At the same time, access to ADCs and the infrastructure required for high-quality pathology remain essential considerations for translating these advances into routine care.
HER2-low is therefore not simply a new label. It is a reminder that, in modern breast oncology, the precision of pathology increasingly determines the precision of treatment.
