RhoGAP domain-containing fusions and PPAPDC1A fusions are recurrent and prognostic in diffuse gastric cancer

We conducted an RNA sequencing study to identify novel gene fusions in 80 discovery dataset tumors collected from young patients with diffuse gastric cancer (DGC). Twenty-five in-frame fusions are associated with DGC, three of which (CLDN18-ARHGAP26, CTNND1-ARHGAP26, and ANXA2-MYO9A) are recurrent in 384 DGCs based on RT-PCR. All three fusions contain a RhoGAP domain in their 3' partner genes. Patients with one of these three fusions have a significantly worse prognosis than those without. Ectopic expression of CLDN18-ARHGAP26 promotes the migration and invasion capacities of DGC cells. Parallel targeted RNA sequencing analysis additionally identifies TACC2-PPAPDC1A as a recurrent and poor prognostic in-frame fusion. Overall, PPAPDC1A fusions and in-frame fusions containing a RhoGAP domain clearly define the aggressive subset (7.5%) of DGCs, and their prognostic impact is greater than, and independent of, chromosomal instability and CDH1 mutations. Our study may provide novel genomic insights guiding future strategies for managing DGCs.