SUMMARY: Prostate cancer is the most common cancer in American men with the exclusion of skin cancer, and 1 in 9 men will be diagnosed with prostate cancer during their lifetime. It is estimated that in the United States, about 174,650 new cases of Prostate cancer will be diagnosed in 2019 and 31,620 men will die of the disease. The development and progression of prostate cancer is driven by androgens. Androgen Deprivation Therapy (ADT) has therefore been the cornerstone of treatment of advanced prostate cancer and is the first treatment intervention.
The intergroup trial developed by the NCIC Clinical Trials Group, in collaboration with the Medical Research Council and the National Cancer Institute US Cancer Therapy Evaluation Program, concluded that the addition of radiotherapy to Androgen Suppression significantly prolongs Overall and Disease Specific Survival, in patients with locally advanced prostate cancer. The optimal duration of Androgen Suppression along with radiotherapy, in the curative management of locally advanced prostate cancer however remains unclear. Neoadjuvant Androgen Suppression schedules have ranged in duration from 3-8 months and for those patients with high risk disease, post radiotherapy adjuvant androgen suppression therapy schedules have ranged from 6-36 months. The study published by Bolla, et al. (NEJM 2009;360:2516-2527) concluded that a combination of radiotherapy along with 6 months of Androgen Suppression provided inferior survival compared with radiotherapy plus 3 years of Androgen Suppression, in patients with locally advanced prostate cancer. This long duration of Androgen Suppression however can be associated with significant adverse events. The PCS IV trial (Nabid, et al. European Urology 2018;74: 432-441) compared 36 months of Androgen Suppression and radiotherapy with 18 months of Androgen Suppression and radiation therapy and concluded that there was no difference in survival between the two treatment groups, with the 18-month group experiencing a better quality of life. Zoledronic acid is effective in preventing Androgen Suppression-induced bone loss, but its role in preventing castration-sensitive bone metastases in locally advanced prostate cancer has been unclear. Randomized Androgen Deprivation And Radiotherapy trial (RADAR) was conducted to determine whether an intermediate duration of Androgen Suppression would be superior to short-term Androgen Suppression, without compromising quality of life. This study was also designed to evaluate whether bisphosphonate therapy would help reduce some of the adverse effects associated with Androgen Suppression and prevent bone disease progression. RADAR trial is randomized, Phase III, 2 × 2 factorial study, which was designed to assess whether the addition of 12 months of adjuvant Androgen Suppression, 18 months of zoledronic acid, or both, can improve outcomes in men with locally advanced prostate cancer, who receive 6 months of Androgen Suppression and radiotherapy to the prostate gland.
This trial enrolled 1071 men 18 years or older with locally advanced prostate cancer, defined as either T2b-4, N0 M0 tumors or T2a, N0 M0 tumors with a Gleason score was 7 or more, and baseline PSA of 10 μg/L or more. Patients were randomly assigned in a 1:1:1;1 ratio to four treatment groups, but all patients following randomization received 6 months of neoadjuvant Androgen Suppression with Leuprolide 22.5 mg IM every 3 months, and radiotherapy to the prostate and seminal vesicles five months after randomization. The four treatment groups were 1) STAS or Short-Term Androgen Suppression which was the control group (N=268), in which patients received 6 months of neoadjuvant Androgen Suppression with Leuprolide 22.5 mg IM every 3 months, and radiotherapy to the prostate and seminal vesicles 2) ITAS or Intermediate-Term Androgen Suppression (N=268), in which STAS was followed by an additional 12 months of adjuvant Androgen Suppression (total of 18 months) with Leuprolide 22.5 mg IM every 3 months 3) STAS plus 18 months of Zoledronic acid 4 mg IV every 3 months, starting at randomization (N=268) 4) ITAS plus Zoledronic acid (N=267). The Primary endpoint was prostate cancer-specific mortality. Secondary endpoints included PSA progression, local progression and distant progression. The median follow up was 10.4 years. Because no interactions were observed between Androgen Suppression and Zoledronic acid at this 10 year follow up, treatment groups were collapsed and 6 months of Androgen Suppression (STAS) plus radiotherapy was compared with 18 months of Androgen suppression (ITAS) plus radiotherapy and groups receiving or not receiving treatment with Zoledronic acid, were compared.
It was noted that the use of additional 12 months of adjuvant Androgen Suppression (total of 18 months) resulted in a significant improvement in prostate cancer specific mortality compared to 6 months of Androgen Suppression and radiotherapy (9.7% versus 13.3% respectively), representing an absolute difference of 3.7% (sub-HR=0.70, adjusted P=0.035). The addition of Zoledronic acid did not have an impact on prostate cancer-specific mortality.
The authors concluded that 18 months of Androgen Suppression plus radiotherapy is a more effective treatment option for locally advanced intermediate and high risk prostate cancer patients, than 6 months of Androgen Suppression plus radiotherapy. It was also concluded that the addition of Zoledronic acid to this treatment regimen does not improve outcomes. Short-term androgen suppression and radiotherapy versus intermediate-term androgen suppression and radiotherapy, with or without zoledronic acid, in men with locally advanced prostate cancer (TROG 03.04 RADAR): 10-year results from a randomised, phase 3, factorial trial. Denham JW, Joseph D, Lamb DS, et al. Lancet Oncol 2019;20:267-281
