Histopathology And Molecular Pathology Investigation Of Rectal Cancer Spreading In Mesorectum

Background:Rectal cancer is one of the most frequent malignant tumors. Its metastases and recurrences are important deadly causes after operation. Recently it is believed that many of these local recurrences are due to incomplete excision of metastasis deposits scattered in the supporting structures around the rectum. Some researchers declared that metastases deposits scattered in mesorectum was an independent prognosis factor. It is very important that the mesorectum containing metastasis deposits be excised in operation to decrease the frequency of recurrences and improve prognosis of rectal cancer patients. In this study,the tumor dissemination in mesorectum is detected by the method detecting tumor micrometastasis that is more efficacious than routine pathology.Objective:To investigate the range of rectal cancer dissemination in mesorectum and confirm the scope of mesorectal excision in the resection of rectal cancer.Material and method:40 colorectal cancer patients who underwent curative operation were included in the study. Tumor,normal intestinal mucous membrane and the mesorectum under the inferior margin of the tumor were obtained from fresh resected specimens. The mesorectum were cut into several sections 1 cm wide on transverse plane at 2cm intervals. Every section was divided into two parts. One was fixed in formalin and embedded in paraffin and then routinely processed for haematoxylin and eosin (H&E) staining in SUM sections. The sections are examined whether the mesorectum is involved. While the other part,tumor and normal intestinal mucous membrane were snap-frozen in liquid nitrogen for RNA preparation. Then they were employed to detect if they were involved by tumor by RT-PCR using carcinoembryonic antigen (CEA) as genetic markers. Results:1,Results of histopathology:The tumor spreading to mesorectum was seen in 6 of 40 patients (15 %) . The route of spread is mainly by directinvasion,forming isolated mesenteric deposits and venous or lymphatics invasion.. The involved mesorectum did not exceed 4cm lower than the inferior tumor margin. Tumor involvement of the mesorectum under tumor margin was seen in 12.5%(5/40) of patients,Involvement of the mesorectum 2cm lower than inferior tumor margin was found in 5%(2/40),4cm was found in 2.5%(1/40). The tumor spreading to mesorectum is correlated with tumor shape> tumor differentiation and the infiltrated depth of bowel wall by tumor,and is not correlated with the size of tumor and the serum level of CEA.2 The expression of CEA mRNA was positive in 38/40 rectal cancer specimens,while 2/40 of the normal intestinal mucous membrane was positive. The expression of CEAmRNA in rectal cancer had statistical discrepancy with that in the normal intestinal mucous membrane. The sensitivity of CEAmRNA expressing in tumor tissue was 95%. The specificity is 87.5%.3 Result of RT-PCR:The metastatic deposits scattered in the mesorectum was seen in 22.5 %(9/40) of patients by RT-PCR. The metastasis was just seen within the range from the mesorectum lying in inferior margin of tumor to the mesorectum 4cm lower than inferior margin of tumor. Tumor involvement of the mesorectum lying in inferior margin of tumor was seen in 22.5%(9/40)of patients,Involvement of the mesorectum 2cm lower than inferior tumor margin was found in 7.5%(3/40),4cm was found in 2.5%(l/40).The tumor spreading to mesorectum is correlated with tumor shape> tumor differentiation and the infiltrated depth of bowel wall,and is not correlated with the size of tumor and the level of CEAConclusion:The metastasis did not exceed the mesorectum 4cm lower than inferior margin of tumor. The range of excision mesorectum would preponderate over confine 5cm lower than the inferior margin of tumor at least in the surgical management of rectal cancer.