Ring Finger 43 Hot-spot Frameshift Mutation G659V in Colorectal Cancer Patients: Report from a Tertiary Cancer Care Hospital in North India.

Background: The Ring Finger 43 (RNF43) is a tumor suppressor gene that negatively regulates the Wnt/β-catenin signaling. The p.G659fs is a recurrent RNF43 C-terminal truncating variant frequent in colorectal cancer (CRC) patients. We aimed to identify this hotspot variant in CRC patients and assessed the relationship between the mutation, clinical characteristics, and tumor β-catenin localization.

Materials and methods: Formalin-fixed, paraffin-embedded tissue samples of upfront, surgically resected, sporadic colorectal adenocarcinoma cases were selected. The p.G659fs mutation was determined by capillary sequencing with sequence-specific primers. Tissue microarray and immunohistochemistry were employed to analyze nuclear β-catenin expression and the expression of mismatch repair (MMR) proteins, respectively. In addition, clinical details were retrieved from the hospital medical records and data were analyzed.

Results: The RNF43 p.G659fs mutation was observed in 8% of CRC patients. In total, 25% of tumors showed a loss of immunostaining for one or more MMR proteins and 14.6% of tumors showed positive nuclear β-catenin staining. The p.G659fs variant was significantly enriched in MMR-deficient tumors (P = 0.04). Importantly, no correlation was observed between the variant and nuclear β-catenin localization (P = 0.48), indicating a Wnt-independent role of this variant in CRC tumors.

Conclusions: To the best of our knowledge, this is the first study from North India to show the involvement of RNF43 p.G659fs variant in CRC patients. The mutation correlated with MMR protein deficiency and seems to be conferring tumorigenicity independent of the Wnt pathway.