EXPRESSION OF P21 AND MUTANT P53 GENE-PRODUCTS IN RESIDUAL PROSTATIC TUMOR-CELLS AFTER RADICAL RADIOTHERAPY

BACKGROUND. In a previous study, sextant core biopsies revealed residu al tumor in the prostate in 37/55 investigated patients, with an avera ge of 6.8 years after external beam radiation therapy (RRT). More than half of the biopsies exhibited Ki-67 and PCNA proliferation activity. METHODS. The present study aims at further characterizing residual tu mor cells post-RRT by investigating whether the tumor cells exhibit im munohistochemical expression of p21 and mutant p53 gene products, whic h reflect the state of cell cycle regulatory mechanisms. RESULTS. Posi tive p53 staining was observed in 11% and p21 positivity in 47% of bio psies. The proportion of positively stained cells was low for both ant igens. The staining patterns point to the existence of wild-type p53-d ependent, as well as alternative pathways for p21 protein induction. C ONCLUSIONS. A low proportion of tumor cells exhibited p53 protein accu mulation post-RRT. G1 arrest, as assessed by p21 immunoexpression, was demonstrated in a low percentage of tumor cells in <50% of post-RRT b iopsies, indicating that the vast majority of residual tumor cells fol lowing RRT escape the G1/S checkpoint control and propagate into S-pha se, presumably with a maintained malignant potential. (C) 1997 Wiley-L iss, Inc.