Metastatic breast cancer in primary lung cancer with compound <em>EGFR</em> mutations: A case report

Yang,Tianyao; Xu,Yifan; Lin,Xi; Chen,Guodong; Wang,Fangfang

doi:10.3892/ol.2026.15481

April-2026 Volume 31 Issue 4

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April-2026 Volume 31 Issue 4

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Case Report Open Access

Metastatic breast cancer in primary lung cancer with compound EGFR mutations: A case report

Authors:
- Tianyao Yang
- Yifan Xu
- Xi Lin
- Guodong Chen
- Fangfang Wang
View Affiliations / Copyright

Affiliations: Department of Breast Surgery, The People's Hospital of Tiantai County, Taizhou, Zhejiang 317200, P.R. China, School of Medicine, Wenzhou Medical University, Wenzhou, Zhejiang 325035, P.R. China

Copyright: © Yang et al. This is an open access article distributed under the terms of Creative Commons Attribution License.
Article Number: 128
|
Published online on: February 9, 2026

https://doi.org/10.3892/ol.2026.15481
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Abstract

The epidermal growth factor receptor (EGFR) is the most common driver gene in the development and progression of non‑small cell lung cancer (NSCLC). Mutations in EGFR exons 18‑21 are frequently observed, particularly exon 19 deletions and the exon 21 L858R point mutations. The T790M mutation in EGFR exon 20 was the first resistance mechanism to tyrosine kinase inhibitors (TKIs) identified in EGFR‑mutant NSCLC. The coexistence of an exon 19 deletion and the exon 20 T790M missense mutation in EGFR is relatively rare, with a low incidence. The incidence of breast metastasis from primary lung cancer ranges from 0.5 to 6.0%, making it an infrequent occurrence. The present study reported a patient with primary NSCLC harboring both an EGFR exon 19 deletion and the exon 20 T790M missense mutations, who developed metastatic breast cancer after being progression‑free for 1 month. Following the Chinese Society of Clinical Oncology and National Comprehensive Cancer Network guidelines for lung cancer, the patient was treated with furmonertinib, a third‑generation targeted antitumor therapy. The present case provides notable insights for the diagnosis and treatment of NSCLC with coexisting EGFR exon 19 deletion and exon 20 T790M missense mutation, and a rare clinical example of breast metastasis from lung cancer.

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