IMMUNOHISTOCHEMICAL DETERMINATION OF P53 OVEREXPRESSION - AN EASY ANDREADILY AVAILABLE METHOD TO IDENTIFY PROGRESSION IN SUPERFICIAL BLADDER-CANCER

Overexpression of p53, as determined by immunohistochemical staining w ith the murine monoclonal antibody DO7, was determined in specimens of 46 primary superficial transitional cell bladder tumours (14 TaG2, 10 T1G2, 22 T1G3). A colon cancer specimen served as a positive control and normal mesenchymal cells in the specimens served as an internal ne gative control. An exceptionally high proportion 36/46 (78%) of the sp ecimens were found to stain positively for p53 in over 20% of the cell nuclei. After a median follow-up of 7 years, ten patients developed p rogressive disease. Of these ten patients nine demonstrated p53 positi vity, resulting in a sensitivity of 90%. However, 27 of the overall 36 patients (75%) with p53-positive rumours did not progress to a higher stage or metastatic disease. These findings suggest that p53 overexpr ession is not of predictive prognostic value in superficial transition al cell carcinoma. With 7 of 14 specimens (50%) of Ta tumours overexpr essing p53, the results were suggestive of p53 mutation being an early event in carcinogenesis. When the threshold was set at 50% of the cel l nuclei overexpressing p53, 16/46 (35%) classified as p53 positive. O f the 16 tumours staining positively for p53, 7 (46%) progressed and 9 (56%) did not. None of the Ta and 16 (50%) of the T1 tumours classifi ed as positive. This more stringent definition of positivity still doe s not identify p53 positivity as a single prognostic factor. With 50% of T1 tumours classifying as positive, we still find that p53 mutation may be an early event in carcinogenesis of bladder cancer.