Main Session
Sep 27
SS 02 - Escalate, De-escalate, or Substitute? Trials Shaping Prostate Cancer Care

109 - Intermittent Androgen Deprivation Therapy with or without Stereotactic Body Radiotherapy for Molecularly Identified Hormone Sensitive Oligometastatic Prostate Cancer: A Randomized Study (i-STOP)

03:40pm - 03:50pm ET
Room 205

Presenter(s)

Patrick Cheung, MD - Sunnybrook Odette Cancer Centre, Toronto, Ontario

R. Glicksman1, D. A. Loblaw2, G. Morton2, H. T. Chung2, D. Vesprini2, S. K. Liu2, W. Chu3, C. L. Tseng2, J. Detsky2, A. Taggar2, J. M. Hudson2, A. AlQaderi4, U. Emmenegger5, V. Escueta2, A. Mamedov2, L. Zhang2, and P. Cheung2; 1Department of Radiation Oncology, University of Toronto, Toronto, ON, Canada, 2Department of Radiation Oncology, Odette Cancer Centre, Sunnybrook Health Sciences Centre, University of Toronto, Toronto, ON, Canada, 3Durham Regional Cancer Centre, University of Toronto, Oshawa, ON, Canada, 4University of Toronto, Toronto, ON, Canada, 5Divsion of Medical Oncology, Sunnybrook Odette Cancer Centre, University of Toronto, Toronto, ON, Canada

Purpose/Objective(s):

Optimal management for PSMA PET-only identified oligometastatic hormone sensitive prostate cancer (omHSPC) remains uncertain.

Materials/Methods:

We conducted a prospective randomized study enrolling patients with synchronous or metachronous omHSPC diagnosed with up to 3 avid areas of metastases identified on PSMA PET with negative conventional staging. Patients were randomized to receive intermittent androgen deprivation therapy (iADT) in 8-month cycles (control arm) or i 8-month cycles with stereotactic body radiotherapy (SBRT) to all metastatic deposits (experimental arm), and prostate-directed radiotherapy if synchronous disease. After the initial 8 months of ADT, re-initiation of ADT occurred when PSA reached > 10 ng/mL, if new metastases developed, or earlier at the discretion of the physician. The primary endpoint was feasibility to randomization (proportion of eligible patients who enroll), with key secondary outcomes of biochemical progression (PSA >25% and >2 plus nadir), PSA nadir, and re-initiation of ADT.

Results:

Between 2021-2024, 77 patients were assessed for eligibility, of whom 66 were eligible, and 60 enrolled on study (91%). Twenty-nine patients were randomized to iADT alone and 31 to iADT and SBRT. At enrollment, most patients (n=58; 97%) had metachronous disease, median PSA 3 ng/mL, and worst location of disease in bone (n=31; 52%) or lymph node (n=26; 43%). Median follow-up was 36 months (IQR 25-47). Cumulative incidence (95% CI) of biochemical progression at 3 years was 60% (37-77%) for iADT alone and 21% (7-41%) for iADT and SBRT (p=0.004). Median time (95% CI) to biochemical progression was 27.3 months (21.4-57.4) for iADT alone and not reached for iADT and SBRT. PSA nadir was median 0.02 ng/mL in both arms, and the proportion of patients who achieved a PSA nadir of <0.2 ng/mL and <0.02 ng/mL was not significantly different between the arms. The cumulative incidence (95% CI) of re-initiation of ADT at 3-years was 41% (19-62%) for iADT alone and 18% (5-36%) for iADT and SBRT (p=0.06), with median PSA at time of re-initiation of ADT 10.3 ng/mL in iADT alone, and 8.4 ng/mL in iADT and SBRT. The median time (95% CI) to re-initiation of ADT was 36.4 months (25.3-57.4) for iADT alone and not reached for iADT and SBRT.

Conclusion:

For patients with PSMA PET-identified omHSPC, the combination of iADT and SBRT significantly improves biochemical progression and prolonged time to re-initiation of ADT compared to iADT alone.