To evaluate the relationship between microsatellite instability (MIN) and histologic types of carcinomas in different organs, we analyzed how often MIN occurred in signet ring cell carcinomas of the colon (7 cases), stomach (13 cases), urinary bladder (5 cases), and prostate (3 cases). We also analyzed MIN and the expression of Epstein-Barr virus encoded RNA (EBER) transcripts in undifferentiated carcinoma with lymphoid stroma: 18 cases of lymphoepithelioma-like carcinoma (LELC) of the colorectum and 8 of the stomach and 9 cases of lymphoepithelial nasopharyngeal carcinoma (NPC). MIN was frequently observed in the signet ring cell carcinomas (4/7, 57%) and LELCs (12/18, 67%) of the colorectum, but was not found in the signer ring cell carcinomas of the urinary bladder or prostate or in NPCs and occurred significantly (p<0.05) less often in both gastric signer ring cell carcinoma (1/13, 8%) and gastric LELCs (1/8, 13%). Most of the gastric LELCs (5/6) and all of the NPCs in which MIN was not identified expressed EBER transcripts. Thus, MIN appear to be specific for signer ring cell carcinomas and LELCs of the colorectum, but there was no strong correlation between MIN and carcinomas in other organs. Different genetic alterations in the different organs could result in the formation of carcinomas of similar types.

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