RSPO1 and colorectal cancer: R-Spondin fusions, including protein tyrosine phosphatase receptor type K-R-Spondin (PTPRK-RSPO3) and eukaryotic transplation initiation factor subunit E/R-Spondin 2 (EIF3E-RSPO2) fusion, have been reported in 4–10 colorectal cancers [100,180].