Previously, we have described a new modification of affinity chromatography columns for isolation of the cytoplasmic, soluble form of tumor-associated antigens (TAA) from the serum of colon cancer patients (Oncol Rep 2: 679-683, 1995). In this communication, we have shown that the main proteins of these TAA were p64 and p53. The correlation coefficient between each of these proteins and the total amount of TAA or total serum protein ranged from 0.55 to 0.93. The serum level of p53 antigen was shown to be related to the tumorigenicity: the correlation and regression coefficients between the serum level of p53 protein and the progress in colon cancer were 0.48 and 0.88, respectively, p<0.001. Therefore, the determination of serum concentration of this protein can serve as a screening tool for cancer detection. The serum level of p53 protein ranges between 0.24 to 0.94 mg/ml in patients with non cancer diseases, and between 1.0 to 2.0 mg/ml in patients with polyposis and in a high risk group, respectively, increases over 2.0 mg/ml in primary colon cancer patients and up to 5.0 mg/ml in cancer patients with metastases. The sensitivity and specificity of our method achieved 92% and 96%, respectively, and accuracy 88%. The presence of p53 protein in the cytoplasm of cells from patients with non cancer diseases may explain why p53 antigen is presented in their sera. Our method can be useful to detect cancer development either as a primary illness or as a recurrent disorder. It is possible to follow up patients with chronic diseases and to detect transformation of these diseases into cancer, or to follow up former cancer patients in order to detect as early as possible incidence of recurrent cancer. It should also be emphasized that our method allows the detection of patients with polyposis or those of high risk groups who exhibit a tendency to develop colon cancer.

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