# Pathological Complete Response after Robot-Assisted Pulmonary Resection Following CDK4/6 Inhibitor–Combined Endocrine Therapy for Endobronchial Oligometastatic Breast Cancer: A Case Report

## TL;DR

A patient with rare endobronchial breast cancer achieved complete response after surgery and CDK4/6 inhibitor-based therapy.

## Contribution

Demonstrates the potential of surgical resection after CDK4/6 inhibitor therapy for endobronchial oligometastatic breast cancer.

## Key findings

- Combination therapy with endocrine therapy and CDK4/6 inhibitor led to tumor regression.
- Surgical resection after systemic therapy resulted in pathological complete response.
- The patient remained progression-free for 1 year and 9 months post-surgery.

## Abstract

Endobronchial metastasis from breast cancer is rare. Even in oligometastatic disease, systemic therapy remains the standard treatment, and the role of surgical resection is not well established. We report a case of endobronchial oligometastatic breast cancer that achieved pathological complete response (pCR) after endocrine therapy combined with a cyclin-dependent kinase 4/6 (CDK4/6) inhibitor, followed by pulmonary resection.

A 48-year-old female with bilateral hormone receptor–positive, human epidermal growth factor receptor 2–negative breast cancer underwent surgery, followed by adjuvant chemotherapy and endocrine therapy. Two years and 8 months later, an elevated NCC-ST-439 level prompted further evaluation, which revealed a lesion in the right bronchus. Bronchoscopic biopsy confirmed metastatic breast cancer. No other metastatic lesions were detected, and the patient was diagnosed with endobronchial oligometastatic disease. Combination therapy with endocrine therapy and a CDK4/6 inhibitor resulted in tumor regression without new metastases. After 9 months of systemic therapy, robot-assisted right lower lobectomy with lymph node dissection was performed. Pathological examination revealed pCR. The patient remains progression-free 1 year and 9 months after surgery.

This case suggests that surgical resection following effective systemic therapy may be a treatment option in selected patients with endobronchial oligometastatic breast cancer.