Does use of apalutamide enhance outcomes in combination with radiotherapy in metastatic hormone-sensitive prostate cancer? A real-world experience from the UK.

Abstract

73 Background: Management of metastatic prostate cancer has undergone a significant change over the past decade, with the introduction of several novel agents and repurposing of others. Latest update from STAMPEDE trials shown prostate radiotherapy (RT) improves OS, without detriment in QoL in metastatic home sensitive prostate cancer mHSPC along with Docetaxel in those with low volume metastatic disease. There is no published data on impact of radiotherapy to prostate on Apalutamide treated mHSPC patients. Here we report our real-world experience of Apalutamide in mHSPC with radiotherapy. Methods: Patients with mHSPC (N = 266) from 5 UK centres, were treated with Apalutamide (240 mg) and ADT along with radiotherapy to prostate as per treating clinician’s discretion. The primary endpoint was objective rate (ORR) as determined by patients achieving a PSA decline of ≥90% (PSA90) and ≥50% (PSA50) and secondary endpoints included biochemical progression free survival (bPFS) and safety. Results: The median age for the whole cohort was 73.4 years (interquartile range 52 - 91), A total of 11.6% had received prior radical treatment (prostatectomy or radiotherapy for localised disease) and 88.4% had de novo metastatic disease. Median baseline PSA was 47 ng/ml (range 0.4-17100). The proportion of patients PSA90 and PSA50 at 3, 6 and 12 months is shown in the Table. Median PSA nadir was 0.1 ng/ml(rage 0.01- 48.2) and median time to reach nadir was 6 months (range 3-24 months). 13.5% (35) patients were treated with radiotherapy (RT) after at least 3 months (range 3 -6 months) of starting apalutamide. Patients received either a daily (55 Gy in 20 fractions over 4 weeks) or weekly (36 Gy in six fractions over 6 weeks) of radiotherapy (68 % vs 32%). Higher number of patients in RT group had achieved PSA90 compared to no radiotherapy cohort (97.14 % vs 87.3%, p =0.15). Patients treated with RT had median post treatment of PSA 0.01 ng/ml compared to 0.1 ng/ml in non RT group (p=0.0062). After median follow up of 8.4 months, proportion of patients shown biochemical progression in RT vs non RT group were 5.7 % vs 15 % respectively (p= 0.04). Patients with de novo metastatic disease have shown poor PSA response and higher chance of progression compared to patients who had initial radical treatment. Radiotherapy was well tolerated, with 17 % adverse events (Radiation Therapy Oncology Group grade 3–4) reported in radiotherapy group. Conclusions: Early experience of using apalutamide and radiotherapy in mHSPC showed improved PSA response and delayed progression. Treatment was well tolerated. Further follow up and clinical trials are needed to understand the impact on overall survival. [Table: see text]