Objective:Mast cells (MC) reside in the mucosa of the digestive tract as the first line against bacteria and toxins.Clinical evidence has implied that the infiltration of mast cells in colorectal cancers is related to malignant phenotypes and a poor prognosis.This study compared the role of mast cells in adjacent normal colon mucosa and in the invasive margin during the progression of colon cancer.Methods:Specimens were obtained from 39 patients with colon adenomas and 155 patients with colon cancers treated at the Sun Yat-sen University Cancer Center between January 1999 and July 2004.The density of mast cells was scored by an immunohistochemical assay.The patt of mast cell distribution and its relationship with dinicopathologic parameters and 5-year survival were analyzed.Results:The majority of mast cells were located in the adjacent normal colon mucosa,followed by the invasive margin and least in the cancer stroma.Mast cell count in adjacent normal colon mucosa (MCCadjacent) was associated with pathologic classification,distant metastases and hepatic metastases,although it was not a prognostic factor.In contrast,mast cell count in the invasive margin (MCCinvasive) was associated with neither the clinicopathlogic parameters nor overall survival.Conclusion:Mast cells in the adjacent normal colon mucosa were related to the progression of colon cancer,suggesting that mast cells might modulate tumor progression via a long-distance mechanism.