Cerebrospinal Fluid Testing in Leptomeningeal Progression of HER2-Negative Breast Cancer Reveals HER2 Positivity, Leading to HER2-Targeted Therapy: A Case Report

TL;DR

A breast cancer patient initially tested HER2-negative but later showed HER2 positivity in cerebrospinal fluid, allowing effective targeted therapy and improved outcomes.

Contribution

Demonstrates how rebiopsy and advanced testing can reveal evolving cancer markers for better treatment options.

Findings

Cerebrospinal fluid testing identified HER2 positivity in a patient with initially HER2-negative breast cancer.

Use of trastuzumab deruxtecan led to significant clinical improvement in the patient.

Rebiopsy and next-generation sequencing can uncover new treatment opportunities in progressing cancers.

Abstract

The treatment of breast cancer is largely determined by protein expression assays of estrogen receptor, progesterone receptor, and Her2/neu (HER2) status. These prognostic markers may vary due to tumor heterogeneityor the evolution of prognostic markers throughout the course of treatment. This report presents a case of a patient who initially presented with HER2-negative breast cancer and had rapidly progressed on numerous lines of treatment. An analysis of cerebrospinal fluid via next-generation sequencing and biopsy of metastasis to the liver identified HER2-positive cancer, which allowed for the use of trastuzumab deruxtecan, a HER2-targeted therapy. This led to an excellent clinical response with improvement in performance status and quality of life. This case report demonstrates the importance of continuing to follow a patient’s cancer pathology to open the doors for other opportunities for treatment. Cancer has the potential to evolve and there is a benefit of obtaining rebiopsies to ensure the correct targeted therapies are provided to the patient.

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