Rare Case of Metastatic NSCLC Mimicking Metaplastic Breast Cancer

By: Julia Cipriano, MS
Posted: Thursday, August 1, 2024

An unusual case of metastatic non–small cell lung cancer (NSCLC) mimicking metaplastic breast cancer was described in JCO Precision Oncology. According to Tanmayi S. Pai, MD, of the Mayo Clinic, Jacksonville, Florida, and colleagues, this patient profile highlights the utility of extended immunohistochemistry and next-generation sequencing for diagnostic and therapeutic decision-making in cases of undifferentiated malignancy.   

“Lung cancer should be considered in the differential diagnosis of metaplastic breast cancer and undifferentiated breast malignancy,” the investigators remarked. “Treatment of these two malignancies can be drastically different, particularly in an era where targeted therapies and immunotherapy have revolutionized the management of metastatic NSCLC.”

A 74-year-old woman presented with a 3.6-cm irregular, circumscribed, symptomatic mass in the upper outer quadrant of the left breast. After undergoing a series of imaging and laboratory assessments, including an inconclusive immunohistochemistry evaluation, she was tentatively diagnosed with triple-negative metaplastic breast cancer. However, given her constitutional symptoms, the investigators remained concerned that the mass reflected metastasis from a nonbreast primary tumor. Based on findings from an extended immunohistochemistry evaluation and simultaneous tissue next-generation sequencing, the patient was found to have metastatic NSCLC with a MET exon 14 skipping mutation.   

The patient completed a course of palliative external-beam radiation therapy (20 Gy) to the left breast, and she began treatment with 400 mg of the tyrosine kinase inhibitor capmatinib twice daily. Although the patient initially achieved a near-partial response, demonstrated a decrease in disease burden, and tolerated the targeted therapy well, she developed oligoprogressive disease of the right adrenal gland after 6 months. Surgical resection was pursued and subsequently intraoperatively aborted. The patient has been referred for palliative radiation therapy and is currently being considered for second-line systemic therapy with carboplatin, pemetrexed, and the PD-1 inhibitor pembrolizumab.

Disclosure: For full disclosures of the study authors, visit ascopubs.org.

JCO Precision Oncology

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