ESTRO 2024 - Abstract Book

S2644

Clinical - Urology

ESTRO 2024

We hypothesised that with local control of oligoprogressive disease (OPD) men can derive ongoing benefit from current systemic therapy, by eliminating and inhibiting seeding of resistant clones and delaying polymetastatic progression. In this multi-centre, phase II prospective, non-randomised trial we assessed if adding SBRT to OPD in patients on androgen receptor targeted agents (ARTA) resulted in median progression free survival (PFS) of > 4 months.

Material/Methods:

Eligible patients had castration resistant prostate cancer (CRPC) with ≤ 2 OPD sites which developed on treatment with an ARTA, after an initial response. All patients were treated with SBRT to a dose of 30 Gy in 5 fractions (alt days) or 36 Gy in 6 fractions weekly (prostate only). The primary endpoint was PFS, triggered by symptoms, prostate specific antigen (PSA), change in treatment and radiological progression or death. Secondary endpoints included time to next therapy, PSA kinetics, overall survival (OS), toxicity (CTCAE) and quality of life (QoL) on EQ5D questionnaire.

Results:

Between 17 th October 2018 to 1 st February 2023, 86 men were recruited. SBRT was delivered to 81 men. Mean age was 74 years. Most patients (67%) had 1 OPD lesion. Sites irradiated were bone (59%), lung (1%), lymph node (32%) and prostate (8%). More patients were on abiraterone (58%) compared to enzalutamide (42%). Median follow-up was 19.2 months at the time of analysis. Fifty-three (65%) patients had progressed, 32 (40%) of patients progressed within 6 months post SBRT. Median PFS post SBRT was 6.4 months (95% CI 5.9-12.8) (Figure 1). Progression-free survival at 12 months is 40.1% (95% CI 28.9-50.9).

Thirty-three (41%) of patients had started new treatment or died. Median time to next treatment was 29.6 months (95% CI 15.8- not reached). Median OS was 34.6 months (95% CI 23.9 – not reached). Of the 43 patients with available PSA results at 3 months post SBRT who did not progress or die within 6 months of SBRT, 36 (84%) patients had greater than 75% reduction in PSA at 3 months post SBRT, compared to 13 (45%) of the 29 patients who progressed or died within 6 months (Figure 2).