Shigeki Sekine1,2, Reiko Ogawa2, Taiki Hashimoto1, Kojima Motohiro3, Hiroshi Yoshida1, Hirokazu Taniguchi1, Yutaka Saito4, Ohno Yasuhiro5, Atsushi Ochiai3, Nobuyoshi Hiraoka1,2. 1. Division of Pathology and Clinical Laboratories, National Cancer Center Hospital, Tokyo, Japan. 2. Division of Molecular Pathology, National Cancer Center Research Institute, Tokyo, Japan. 3. Division of Pathology, Research Center for Innovative Oncology, National Cancer Center, Kashiwa, Chiba, Japan. 4. Endoscopy Division, National Cancer Center Hospital, Tokyo, Japan. 5. Endoscopy Division, National Cancer Center Hospital East, Kashiwa, Chiba, Japan.
Abstract
AIMS: Traditional serrated adenoma (TSA) is a rare but distinct type of colorectal polyp. Our previous study showed that PTPRK-RSPO3 fusions are frequent and characteristic genetic alterations in TSAs. This study aimed to characterize comprehensively the prevalence and variability of RSPO fusions in colorectal TSAs. METHODS AND RESULTS: We examined RSPO expression and explored novel RSPO fusions in 129 TSAs, including 66 lesions analysed previously for WNT pathway gene mutations. Quantitative polymerase chain reaction (qPCR) analyses identified three and 43 TSAs overexpressing RSPO2 and RSPO3, respectively, whereas the expression of RSPO1 and RSPO4 was marginal or undetectable in all cases. RSPO overexpression was always mutually exclusive with other WNT pathway gene mutations. Known PTPRK-RSPO3 fusions were detected in 37 TSAs, all but one of which overexpressed RSPO3. In addition, rapid amplification of cDNA ends revealed three novel RSPO fusion transcripts, an NRIP1-RSPO2 fusion and two PTPRK-RSPO3 fusion isoforms, in six TSAs. Overall, 43 TSAs had RSPO fusions (33%), whereas four TSAs (3%) overexpressed RSPO in the absence of RSPO fusions. TSAs with RSPO fusions showed several clinicopathological features, including distal localization (P = 0.0063), larger size (P = 0.0055), prominent ectopic crypt foci (P = 8.4 × 10-4 ), association of a high-grade component (P = 1.1 × 10-4 ), and the presence of KRAS mutations (P = 4.5 × 10-5 ). CONCLUSIONS: The present study identified RSPO fusion transcripts, including three novel transcripts, in one-third of colorectal TSAs and showed that PTPRK-RSPO3 fusions were the predominant cause of RSPO overexpression in colorectal TSA.
AIMS: Traditional serrated adenoma (TSA) is a rare but distinct type of colorectal polyp. Our previous study showed that PTPRK-RSPO3 fusions are frequent and characteristic genetic alterations in TSAs. This study aimed to characterize comprehensively the prevalence and variability of RSPO fusions in colorectal TSAs. METHODS AND RESULTS: We examined RSPO expression and explored novel RSPO fusions in 129 TSAs, including 66 lesions analysed previously for WNT pathway gene mutations. Quantitative polymerase chain reaction (qPCR) analyses identified three and 43 TSAs overexpressing RSPO2 and RSPO3, respectively, whereas the expression of RSPO1 and RSPO4 was marginal or undetectable in all cases. RSPO overexpression was always mutually exclusive with other WNT pathway gene mutations. Known PTPRK-RSPO3 fusions were detected in 37 TSAs, all but one of which overexpressed RSPO3. In addition, rapid amplification of cDNA ends revealed three novel RSPO fusion transcripts, an NRIP1-RSPO2 fusion and two PTPRK-RSPO3 fusion isoforms, in six TSAs. Overall, 43 TSAs had RSPO fusions (33%), whereas four TSAs (3%) overexpressed RSPO in the absence of RSPO fusions. TSAs with RSPO fusions showed several clinicopathological features, including distal localization (P = 0.0063), larger size (P = 0.0055), prominent ectopic crypt foci (P = 8.4 × 10-4 ), association of a high-grade component (P = 1.1 × 10-4 ), and the presence of KRAS mutations (P = 4.5 × 10-5 ). CONCLUSIONS: The present study identified RSPO fusion transcripts, including three novel transcripts, in one-third of colorectal TSAs and showed that PTPRK-RSPO3 fusions were the predominant cause of RSPO overexpression in colorectal TSA.
Authors: Sam O Kleeman; Viktor H Koelzer; Helen Js Jones; Ester Gil Vazquez; Hayley Davis; James E East; Roland Arnold; Martijn Aj Koppens; Andrew Blake; Enric Domingo; Chris Cunningham; Andrew D Beggs; Valerie Pestinger; Maurice B Loughrey; Lai-Mun Wang; Tamsin Rm Lannagan; Susan L Woods; Daniel Worthley; S Cort Consortium; Ian Tomlinson; Philip D Dunne; Timothy Maughan; Simon J Leedham Journal: Gut Date: 2019-09-28 Impact factor: 23.059