Phase 2b trial results of padeliporfin (WST11 or Tookad) vascular-targeted photodynamic therapy for partial gland ablation in men with intermediate-risk prostate cancer

Coleman, J.; Sjoberg, D. D.; Demac, Q.; Odea, C.; McGill, M.; Tracey, A.; Nogueira, L.; Vickers, A.; Estes, C.; Fine, S.; Akin, O.; Mulhall, J.; Sandhu, J.; Carver, B. S.; Laudone, V. P.; Ehdaie, B.; Scherz, A. J.; Scardino, P. T.; Eastham, J. A.

Background: Padeliporfin (WST11) vasculartargeted photodynamic therapy (VTP) has shown significant clinical benefit as a localized partial gland ablation (PGA) therapy when compared to active surveillance for low-risk prostate cancer, by curbing progression and the need for radical treatment, leading to its regulatory approval in Europe. This phase 2b trial prospectively investigated WST11-VTP for intermediate-risk cancers. Methods: Men with unilateral Grade Group 2 (GG2) cancers (Gleason 3+4), evaluated with MRI and ultrasound-guided (TRUS) biopsy, underwent up to two WST11-VTP PGA sessions. Eligibility criteria included <cT2b, PSA < 10, and fusion biopsy for PIRADS 3+ lesions on pretreatment MRI. Contralateral very low-risk disease was observed. The primary endpoint was prevalence of any Gleason Grade 4 or 5 (≥GG2) cancer, determined by MRI and systematic, 14-core TRUS biopsy of the entire gland (+/- fusion) at 3 and 12 months after treatment. Treatment safety and patient-reported quality of life for sexual and urinary function were assessed with validated questionnaires (IIEF-15 and IPSS, respectively). The study was powered using β = 0.2 to reject the null hypothesis (r≤70%), using a one-sided exact binomial test with 5% alpha risk. To be valid, 44 evaluable patients were required for the 12-month primary endpoint assessment. Results: Of the 50 men treated, 46 were evaluable for the 12-month primary endpoint. Before 12 months, 1 man proceeded to prostatectomy (treatment failure), 2 men refused 12-month biopsy, and 1 man died of COVID-19. At 3 months, 12/49 (24%) men underwent per protocol second WST11-VTP PGA session for GG2 tumor: 9 for residual cancer and 4 for newly identified contralateral GG2 tumors (1 bilateral). The 12-month biopsy was performed in 45 men;38 (83%) had no Gleason grade 4 or 5 cancer, including 11/12 (92%) patients who underwent 2 PGA sessions. By 3 months, median decline in erectile function score (IIEF-5) from baseline was -1.0 (IQR -7,0). Median improvement in urinary function score (IPSS) was -1.0 (IQR -1,5), with pad-free continence observed in all patients. Median change in IIEF score by 12-months was -1.0 (IQR -5,0). Grade 3 treatment-related adverse events occurred in 6 (12%) patients. All procedurerelated prostate/pelvic pain resolved by 3 weeks. Conclusions: The positive results from this trial show that WST11-VTP is effective for PGA of intermediate-risk prostate cancer, with minimal toxicity or impact on urinary and sexual function, consistent with the phase 3 trial results in low-risk disease. Based on these data, this therapy bears consideration for approval as a conservative therapeutic option for selected cases of intermediate-risk disease.