Abstract
5017 Background: Retrospective studies suggest that p53 mutation and associated immunohistochemical (IHC) detectable expression are prognostic for recurrence in pts with organ confined UBC and may be predictive for benefit from MVAC adjuvant chemotherapy. Methods: Pts with pT1–2N0M0 UBC following radical cystectomy and bilateral pelvic lymph node dissection were eligible. IHC for p53 was centrally performed and pts with ≥10% nuclear reactivity were offered randomization to 3 cycles of adjuvant MVAC vs. observation. P53 negative and p53 positive pts who declined randomization were observed. Primary endpoint was recurrence-free survival (RFS) in the randomized population. Secondary endpoints were RFS in p53 negative versus p53 positive pts and overall survival in each of these groups. Using a one-sided log-rank test with α = 0.05 and β = 0.15, 190 p53 positive patients were planned to be randomized to detect an absolute improvement in RFS at 3 years (yrs) from 50% to 70% (corresponding hazards ratio of 0.51). Results: 521 pts were registered, 499 underwent successful p53 assessment (male: 80%, <65 yrs: 57%, Caucasian: 91%, pathologic stage P1/P2: 37%/63%, lymphovascular invasion: 20% yes/28% unknown), 272 (55%) were p53 positive and 114 were randomized (42%). Further accrual was halted based on data safety monitoring board review of futility analysis on the first 100 randomized pts. P53 positive tumors were higher grade (97% vs 93% grade 3/4, p = 0.04) and less likely to express p21 (59% vs 84%, p < 0.001). Overall 5-yr RFS was 80 ± 2% with no difference based on p53 status. P53 positive patients declining were older but otherwise similar to those accepting randomization. Only 67% of pts randomized to MVAC received all 3 cycles with 12 (21%) receiving none. There was no difference in RFS in the randomized population (overall 5 yr RFS 83 ± 4%, hazard ratio = 0.88, p = 0.78). Conclusions: The prognostic and predictive value of p53 IHC were not confirmed in this prospective study, but the lower than expected event rate and failures to receive assigned therapy severely compromised the study's power. The value of p53 mutations is being assessed. No significant financial relationships to disclose.