PCDH11X and neoplasm: Of the eight identified ESR1 fusions from all datasets that were PCR validated (Figure S1), only three in-frame fusions, ESR1-e6>YAP1 and ESR1-e6>PCDH11X from advanced disease and ESR1-e6>NOP2 from a primary tumor that showed subsequent resistance to endocrine therapy, produced stable proteins when expressed as cDNA, allowing further study (Figure 1B).