Ireland is now part of a major international study called DESTINY‑Breast15, which brings new treatment options to people with types of breast cancer that until recently had very few targeted treatments available.

What Is DESTINY‑Breast15?

DESTINY‑Breast15 (Clinical Trial ID: NCT05950945) is a Phase 3 clinical trial now open at St. Vincent’s University Hospital. The trial is testing a treatment called trastuzumab deruxtecan (also known as T-DXd) for adults whose cancer has spread or returned (advanced or metastatic) and whose tumours show low or no HER2 protein (HER2 IHC 0 or 1+).

The main goal of the study is to find out how long patients benefit from this treatment before needing to start a different one, a timeframe called Time to Next Treatment (TTNT).

What Is Trastuzumab Deruxtecan?

Trastuzumab deruxtecan is a type of medicine known as an antibody-drug conjugate. This means it works in two steps to target cancer cells while protecting healthy parts of the body:

• The “finder” part (monoclonal antibody): The drug contains a special protein that acts like a smart guide, traveling through the body to find cancer cells by recognizing a specific marker on their surface.
  
  
• The “treatment” part (chemotherapy): Once it attaches to a cancer cell, it delivers chemotherapy directly inside the cell.

This targeted approach attacks the cancer cells from within, helping to reduce side effects compared to traditional chemotherapy.

Who Can Take Part?

You might be able to join the trial if you:

• Are 18 years or older.
  
  
• Have breast cancer that cannot be removed by surgery or has spread (unresectable or metastatic).
  
  
• Have HER2-low (IHC 1+ or 2+) or HER2-zero (IHC 0) status.
  
  
• Have had no more than two prior treatments for metastatic disease.

Why This Trial Is Important

This trial is part of a new wave of research focused on breast cancers with little or no HER2 protein. Until now, these types of breast cancer didn’t have treatments that specifically target HER2 because their protein levels were too low. HER2 is a protein that can help cancer grow, and cancers with higher HER2 levels often respond well to HER2-targeted treatments, which have been shown to improve survival rates.

New medicines like trastuzumab deruxtecan are now showing they can help even when HER2 levels are low or almost absent. Earlier studies showed promising results, including longer survival for patients, and this trial aims to make this treatment available to more people.

Interested in Taking Part?

If you think this trial might be right for you, speak with your oncologist. They can help you understand if you meet the criteria and guide you through the next steps.