Assessing racial differences in time to treatment escalation following androgen-deprivation therapy among veterans with prostate cancer.
Authors: Friedrich Nadine Adriana , Janes Jessica , Parrish Joshua , De Hoedt Amanda Marie , Pruett Janis , Fallick Mark , Gandhi Raj , Zhu Emily , Morlock Robert , Freedland Stephen J. 
Published: June 2023

5078 Background: Androgen deprivation therapy (ADT) is standard care first-line (1L) systemic treatment for advanced and metastatic prostate cancer (PC). Currently, there are no population-level studies assessing the duration of 1L ADT and time to treatment escalation (chemotherapy [CT], novel hormonal therapy [NHT], or non-steroidal antiandrogen [NSAA]). Methods: We performed a retrospective population-level analysis to assess the association between race and time to treatment escalation after ADT in the Veterans Affairs Health Care System. From 2001-2021, 164,477 patients (pt) diagnosed with PC and treated with ADT alone were identified. Baseline demographic and clinical characteristics were sorted by race: Non-Hispanic White (NHW), Non-Hispanic Black (NHB), Hispanic, Other and compared among groups using chi square tests for categorical variables and Kruskal-Wallis tests for continuous variables. The primary outcome was time from ADT to treatment escalation, defined as receipt of NHT, NSAA, or CT. Men with no evidence of treatment escalation were censored at time of death or most recent visit. We estimated 5-year event rates by race using Kaplan-Meier (KM) analyses. Univariable and multivariable Cox proportional hazards models were used to test the association between race and time to treatment escalation with time of ADT as time zero. Multivariable models were adjusted for age, year, time from PC diagnosis to ADT, Charlson Comorbidity Index and BMI at ADT start along with PSA, testosterone level, and receipt of radiation therapy (RT) prior to ADT. Results: NHB were youngest (p<0.001), started ADT in more recent years (p<0.001), had the highest pre-ADT PSA (p<0.001) and testosterone levels (p<0.001), the most comorbidities (p<0.001), and the highest rate of RT prior to ADT (p<0.001) relative to other groups. During a median (Q1, Q3) follow-up of 55.2 (25.0, 102.4) months, 31,288 pt (19%) had treatment escalation, of which 12,093 (39%) were NHTs, 14,842 (47%) were NSAAs, 3,895 (12%) were CT and 458 (2%) were other 2nd line therapies. Compared to NHW, NHB had significantly lower rate of treatment escalation in univariable (HR=0.89, 95% CI=0.87-0.92) and multivariable analysis (HR=0.82, 95% CI=0.80-0.84). KM estimates at 5-year for the percent free from escalation was 80.5 (80.2-80.8%) in NHW vs. 83.0 (82.6-83.4%) in NHB. Rate of treatment escalation was similar for Hispanics and other races compared to NHW, with 5-year KM estimates of 81.0 (80.3-81.7%) and 81.0 (80.0-82.0%) for Hispanics and other races, respectively. Conclusions: This study assessing racial differences in time to treatment escalation of men receiving 1L ADT found that NHB had a significantly lower rate of treatment escalation. Whether this decreased rate of treatment escalation among NHB men represents improved outcomes (i.e. lower risk of progression) or undertreatment requires further study.