# Trastuzumab Deruxtecan‐Induced Pneumonitis: Case Series

## TL;DR

This paper reports three cases of pneumonitis in breast cancer patients treated with trastuzumab deruxtecan, highlighting the need for early detection and corticosteroid use.

## Contribution

The study provides a case series of T-DXd-induced pneumonitis in Saudi Arabia, emphasizing clinical management strategies.

## Key findings

- Pneumonitis occurred after 2–9 cycles of T-DXd in three HER2-positive breast cancer patients.
- Symptoms included cough and dyspnea, with HRCT showing ground-glass opacities.
- All patients required corticosteroids and permanent treatment discontinuation.

## Abstract

Trastuzumab deruxtecan (T‐DXd) is a HER2‐targeted antibody–drug conjugate with proven efficacy in metastatic breast cancer, but interstitial lung disease (ILD) and drug‐induced pneumonitis are potentially life‐threatening toxicities. We retrospectively reviewed three patients with HER2‐positive metastatic breast cancer treated with T‐DXd at a tertiary hospital in Saudi Arabia who subsequently developed pneumonitis. Pneumonitis developed after 2–9 cycles of T‐DXd, presenting with cough, dyspnea, and ground‐glass opacities. All patients received corticosteroids and required permanent discontinuation. Early recognition and multidisciplinary management of T‐DXd‐induced pneumonitis are essential. Clinicians should monitor respiratory symptoms and apply timely corticosteroid therapy.

Trastuzumab deruxtecan may cause early or late‐onset pneumonitis or ILD. Nonspecific respiratory symptoms require prompt high‐resolution computed tomography (HRCT) evaluation. Early diagnosis and corticosteroid treatment, along with timely treatment interruption or discontinuation, are essential to prevent progression to severe or fatal toxicity, particularly in heavily pretreated metastatic breast cancer patients.

Three women with HER2‐positive metastatic breast cancer developed pneumonitis or interstitial lung disease after 2–9 cycles of trastuzumab deruxtecan. Presentations ranged from mild cough to CT‐confirmed ILD, often requiring corticosteroids and treatment interruption or discontinuation. Early recognition and multidisciplinary management are essential to minimize morbidity.