A woman presented to medical oncology with almost 4 years of untreated, slowly progressing, triple negative metastatic breast cancer to the lung. About 15 years prior, she was diagnosed with invasive ductal carcinoma of the right breast with ipsilateral chest wall recurrence 6 years later. Comprehensive molecular profiling of a metastatic lesion detected a hotspotETV6-NTRK3fusion, which was not present on circulating tumour DNA or molecular profile performed 4 years prior. A second look pathological examination demonstrated tumour characteristics consistent with secretory breast carcinoma. Identification ofETV6­-NKRT3fusion allowed for treatment with larotrectinib, a tyrosine kinase inhibitor specifically indicated for secretory breast carcinoma. After 3 months, she experienced a partial response.

This commentary discusses the case from the publication “Metastatic Triple Negative Breast Cancer with NTRK Gene Fusion on Tissue but not on ctDNA Molecular Profile.” This paper stresses the importance of molecular profiling to find characteristic mutations such as NTRK gene fusions which increase therapeutic options including tyrosine receptor kinase inhibitors such as Larotrectinib and entrectinib. The current profiling techniques are also discussed with both advantages and limitations discussed. Genomic testing in relation to current pharmaceutical therapies will shape the future of cancer diagnosis and treatment.