Driver vs. passenger: Primary resistance to larotrectinib in synovial sarcoma harboring concurrent SS18 rearrangement and PDE3A-NTRK2 fusion
Synovial sarcoma (SS) is molecularly defined by the pathognomonic SS18::SSX fusion, a master epigenetic driver. While NTRK gene fusions are high-priority tissue-agnostic targets for TRK inhibitors like larotrectinib, their co-occurrence with established lineage-defining drivers in sarcomas is exceptionally rare and presents a therapeutic paradox.

