RSPO1 and cancer: Here, we detected and validated two unreported canonical R-spondin fusions in cancer cell lines derived from biliary tract (EGI-1; PTPRK-RSPO3 fusion) and esophagus (ESO51; EIF3E-RSPO2 fusion) by PCR and FISH (Fig. 5a and Supplementary Fig. 5a, b and c).