# Exceptional responses to Trastuzumab deruxtecan in HER2-positive breast cancer: two illustrative case reports

## TL;DR

Two patients with HER2-positive breast cancer experienced long-lasting remission after treatment with Trastuzumab deruxtecan, suggesting potential for durable responses beyond conventional expectations.

## Contribution

Demonstrates the potential for long-term remission with Trastuzumab deruxtecan in metastatic HER2-positive breast cancer through two exceptional case reports.

## Key findings

- One patient had a complete remission for 36 months after treatment discontinuation.
- Another patient maintained disease control for over 39 months with prolonged treatment pauses.
- These cases suggest T-DXd may induce durable responses and long-term remission in selected patients.

## Abstract

Trastuzumab deruxtecan (T-DXd), an antibody-drug conjugate targeting human epidermal growth factor receptor 2 (HER2), has demonstrated substantial clinical activity in metastatic HER2-positive breast cancer. Although durable responses are increasingly reported, the potential for long-lasting remission after treatment discontinuation remains poorly documented.

We report two patients with metastatic HER2-positive breast cancer who experienced exceptional and sustained clinical benefit with T-DXd. The first patient achieved a deep response lasting over 50 months, including 36 months of complete remission after treatment discontinuation due to thrombocytopenia. The second patient has maintained disease control for over 39 months, with a prolonged treatment pause. Both cases highlight remarkable disease stability beyond conventional expectations.

These case reports highlight the potential of T-DXd not only to induce deep and durable responses but also to maintain disease remission beyond drug exposure in selected patients. Such observations challenge the paradigm of incurability in metastatic HER2-positive breast cancer and warrant further investigation into the mechanisms and predictors of long-lasting responses.