MP22-20\u2003ASSESSING THE IMPACT AND PREDICTORS OF OTHER-CAUSE MORTALITY IN PATIENTS TREATED WITH POST-PROSTATECTOMY SALVAGE RADIATION THERAPY IN ORDER TO AVOID POSSIBLE OVERTREATMENT: RESULTS FROM A LARGE, MULTI-INSTITUTIONAL STUDY

Abstract

INTRODUCTION AND OBJECTIVES: Salvage radiation therapy (SRT) represents a potential curative treatment option for prostate cancer (PCa) patients with rising PSA after radical prostatectomy (RP). However, SRT may be itself associated with a possible overtreatment, especially in elderly men at high risk of dying from other causes. We hypothesized that the impact of OCM varies significantly by patient and tumour characteristics as well as by the use of concomitant hormonal treatment (cHT) METHODS: The study included 762 patients who received SRT at seven referral centres for PSA rising after RP. The irradiation of the pelvic lymph nodes area and the administration of cHT were left at the discretion of the treating physician. The primary outcome consisted of OCM after SRT. Stratified cumulative incidence Poisson plots were generated according to age (<66 vs. ≥ 66 years old) and HT use (no vs. yes), in patients treated with early (PSA ⩽0.5 ng/ml) and late (PSA >0.5 ng/ml) SRT. Multivariable competing-risks regression (CRR) analysis was used to test the association between OCM and all the following covariates: age at SRT, pT stage, pathologic Gleason score, pN stage, PSA at SRT, cHT use, and SRT dose. Finally, interaction terms between age, use of cHT, and PSA at SRT were tested RESULTS: Median patient age was 66 years. Concomitant HT was administered to 165 (22%) patients, whereas 240 (31%) patients had PSA at RT >0.5 ng/ml. Overall, 14% of the patients died of other-cause at 10-year follow-up. After stratification, the highest OCM rate was recorded in elderly patients who received early SRT with cHT (29%). At multivariable CRR analyses, age (HR: 1.07, p=0.002) and cHT (HR: 2.56, p=0.043) were associated with the risk of OCM. Similarly, interaction term between age and HT use showed a detrimental effect of the use of HT in elderly patients (HR: 10.39, p<0.001) relative to young patients who did not receive HT. Finally, the multiple interaction between elderly patients, use of cHT, and early SRT showed a strong effect on OCM (HR 16.10, p<0.001) relative to young patients who received early SRT without cHT CONCLUSIONS: Advanced age and concomitant use of HT are strongly associated with higher rates of OCM in patients treated with post-prostatectomy SRT. Moreover, our data suggest a detrimental effect of the combination of HT use and early SRT in elderly patients. These patients might be those who less benefit from an aggressive salvage treatment given their risk of OCM Source of Funding: None