Background/aims: Although primary small intestinal carcinoma (SIC) is morphologically similar to colorectal carcinoma and shares many of the genetic changes of carcinogenesis, little is known about the role of defective mismatch repair (MMR) genes involved in the SIC. The aim of this study is to investigate the role of defective MMR genes and correlation between clinicopathological factors and loss of MMR protein in SIC.
Methodology: A total of 195 SIC cases were collected from 20 institutions in Korea and tissue microarrays (TMA) were made. The loss of expression of hMLH1, hMSH2 and hMSH6 was examined by immunohistochemistry (IHC).
Results: The loss of expression of hMLH1, hMSH2 and hMSH6 was identified in 25/193 (13.0%), 25/193 (13%) and 29/195 (15%), respectively. The loss of hMSH2 expression was associated with retroperitoneal seeding. Patients with loss of hMSH6 expression had a tendency to invade deeply and a higher frequency of pancreas invasion. The loss of hMSH6 expression was associated less frequently with peritumoral adenoma. There was no survival difference by MMR protein expression status.
Conclusions: The loss of MMR protein was associated with some distinct clinicopathological features. MMR pathway seems to be major pathway in carcinogenesis of SICs. MMR defect seems to be related with sporadic-microsatellite instability (MSI).