# Excellent efficacy of trastuzumab deruxtecan in a patient with HER2-positive advanced breast cancer complicated by pulmonary lymphangitic carcinomatosis: a case report and literature review

## TL;DR

A patient with HER2-positive breast cancer and lung complications showed long-term improvement with a new drug called trastuzumab deruxtecan.

## Contribution

This is the first reported case showing trastuzumab deruxtecan's effectiveness in treating breast cancer with pulmonary lymphangitic carcinomatosis.

## Key findings

- The patient achieved 14.2 months of progression-free survival after T-DXd treatment.
- T-DXd showed therapeutic potential in HER2-positive breast cancer with pulmonary lymphangitic carcinomatosis.
- The case suggests T-DXd could be effective where prior treatments failed.

## Abstract

Trastuzumab deruxtecan (T-DXd or DS-8201), as a novel antibody–drug conjugate, has demonstrated good efficacy in HER2-positive advanced breast cancer. However, its effectiveness in treating pulmonary lymphangitic carcinomatosis (PLC) has not been previously reported. This paper presents a case of a HER2-positive advanced breast cancer patient who experienced disease progression after treatment with trastuzumab and pertuzumab. The patient developed multiple metastases along with PLC and subsequently received T-DXd treatment, achieving 14.2 months of progression-free survival (PFS). This case is the first to reveal the therapeutic potential of T-DXd in breast cancer patients with PLC.