P53 IMMUNOSTAINING DISTINGUISHES MALIGNANT FROM BENIGN LESIONS OF THE GALLBLADDER

The expression of p53 protein was studied in formalin-fixed paraffin-embedded specimens of 41 well-differentiated adenocarcinomas of the gall-bladder, six cases of acute cholecystitis and 23 cases of chronic cholecystitis, using a monoclonal p53 (PAb 1801) antibody and streptavidin-biotin. p53 staining was divided into diffuse, focal or sporadic patterns. The relationship between the p53 Labeling Index (p53 LI) and cellular proliferation was also investigated using monoclonal Ki-67 (MIB1) antibody. Twenty-four of the 41 carcinomas (58.5%) had a diffuse staining pattern with a high p53 LI (47-93%) and 9.8% (4/41) had a focal staining pattern with an intermediate p53 LI (22-34%), with no relation to pT stage, tumor size, histologic type or grade of cytologic atypia, The p53 LI was higher than the Ki-67 LI in these tumors except for one. On the other hand, p53 staining was completely sporadic in the non-neoplastic specimens with a low p53 LI (0.2-2.8%). The p53-positive cells in these specimens were located only within areas of Ki-67-positive cells. In conclusion, p53-protein overexpression occurs as an early event in approximately 70% of well-differentiated adenocarcinomas of the gall-bladder, and this alteration is maintained during progression from intramucosal to invasive carcinoma. p53 immunostaining can distinguish malignant from benign lesions of the gall-bladder.