Excellent Response to MEK Inhibition in an AGK-BRAF Gene Fusion Driven Carcinoma: Case Report and Literature Review

Background: Soft tissue myoepithelial carcinomas (STMC) are a rare, malignant subgroup of myoepithelial tumors that arise typically in glandular or ductal tissues, but also in the bone and soft and cutaneous tissues. Due to its rarity, there is no consensus regarding the treatment of STMC, including chemotherapy or other systemic agents for metastatic STMC. Case Report: A chemotherapy- and regorafenibrefractory STMC, harboring an AGK-BRAF fusion, was successfully treated using MEK-inhibition with cobimetinib in monotherapy. MEK-inhibition with cobimetinib effectively silenced paradoxical MAP kinase/ERK-signaling pathway activation after regorafenib monotherapy, and resulted in a significant and durable clinical response. Conclusion: This effect of MEK-inhibition in STMC harboring an AGK-BRAF fusion has not been previously reported and contributes to the existing, yet limited, knowledge on the treatment of BRAF fusion-driven tumors. Also, our case highlights the importance of next generation sequencing in driving further rational therapeutic choices to provide disease control and palliation.