Response to Pralsetinib in Multi-Drug-Resistant Breast Cancer With CCDC6-RET Mutation.

Triple-negative breast cancers (TNBC) represent a pathological subtype of breast cancer, which are characterized by strong invasiveness, high metastasis rate, low survival rate, and poor prognosis, especially in patients who have developed resistance to multiline treatments. Here, we present a female patient with advanced TNBC who progressed despite multiple lines of treatments; next-generation sequencing (NGS) was used to find drug mutation targets, which revealed a coiled-coil domain-containing protein 6 (CCDC6)-rearranged during transfection (RET) gene fusion mutation. The patient was then given pralsetinib, and after one treatment cycle, a CT scan revealed partial remission and adequate tolerance to therapy. Pralsetinib (BLU-667) is a RET-selective protein tyrosine kinase inhibitor that can inhibit the phosphorylation of RET and downstream molecules as well as the proliferation of cells expressing RET gene mutations. This is the first case in the literature of metastatic TNBC with CCDC6-RET fusion treated with pralsetinib, an RET-specific antagonist. This case demonstrates the potential efficacy of pralsetinib in cases of TNBC with RET fusion mutations and suggests that NGS may reveal new opportunities and bring new therapeutic interventions to patients with refractory TNBC.