ABSTRACT
The heterogeneous nature of tumour antigen expression may require the selection of monoclonal antibodies on an individual tumour to allow its adequate localization. Epithelial Membrane Antigen [EMA] and Cytokeratins [CK] expressions are not previously been compared in colorectal cancer patients. Sections of colorectal cancer [n= 32] were examined by monoclonal antibodies to EMA; CK. In the normal mucosa adjacent to the tumours, EMA was weakly expressed in 8 cases [25%], and negative in 24 cases [75%] recording mean weighted score of 0.43[ +/- 0.84]. CK expression was positive in the normal mucosa in all cases [100%] recording mean weighted score of 10.4 [ +/- 2.01]. This indicates that EMA is more specific marker than CK in colorectal carcinomas [80% and 50% respectively]. All primary colorectal cancers expressed EMA [100%] while 30 of 32 expressed CK [93.7%]. These results suggest that EMA is more sensitive than CK expression for colorectal cancer. The mean weighted score of EMA staining density was 6.4 [ +/- 4.2] in all grades while it recorded 6.8 [ +/- 4.5] for CK staining density. These results showed no significant difference between EMA and CK expression in all grades of differentiation of the tumours, and highly significant differences in their expression in the normal mucosa when compared with that in the malignant tissue [P<0.005]. Regarding tumour staging; the mean weighted score of EMA staining density was 8.57 [ +/- 4.07] in Dukes stage A; it recorded 4.75[ +/- 4.55] in stage B7 and 6.29[ +/- 4.07] in stage B2. The mean weighted score of CK staining density was 4.14 [ +/- 4.33], 5.87 [ +/- 4.35] and 8.35[ +/- 4.22] respectively. There were no significant differences in EMA expression in the different stages of colorectal carcinoma while CK expression in stages A and B1 and stage B2 was significantly different. EMA expression is negatively correlated with the tumour grade of differentiation and stage, while CK expression was negatively correlated with the tumour grade of differentiation and positively correlated with the stage of colorectal cancer. The combinations of monoctonal antibodies directed against distinct tumour - associated antigens such as EMA and CK may overcome the problem of heterogeneity of antigen expression and improve both the immunolocalization and potential for targeted therapy of monoclonal antibodies to patients with colorectal cancer. These findings lead us to recommend the selection of both Cytokeratins and Epithelial Membrane Antigen as prognostic factors in colorectal carcinoma. Thus selecting monoclonal antibodies markers based on tumour biopsies allow improved tumour localization for imaging or therapy in patients with colorectal cancer