Study EV-103: Neoadjuvant treatment with enfortumab vedotin monotherapy in cisplatin-ineligible patients (pts) with muscle invasive bladder cancer (MIBC): Updated results for Cohort H.

4595 Background: Cisplatin-ineligible pts with MIBC have no established neoadjuvant treatment options known to prolong survival before undergoing radical cystectomy and pelvic lymph node dissection (RC+PLND), Enfortumab vedotin (EV) is an antibody-drug conjugate directed to Nectin-4, which is highly expressed in urothelial cancer. In a phase 3 study, EV showed improved overall survival vs standard chemotherapy and a tolerable safety profile in pts with advanced urothelial cancer previously treated with a platinum agent and a PD-1/L1 inhibitor (Powles NEJM 2021). In Cohort H of the EV-103 phase 1b/2 study, preliminary results, including pathological complete response (pCR) and pathological downstaging (pDS) rates, showed antitumor activity in cisplatin-ineligible pts with MIBC who received neoadjuvant EV treatment (Petrylak ASCO GU 2022). Here we report updated results, including event-free survival (EFS) and subsequent cancer-related therapy. Methods: Cohort H of the EV-103 phase 1b/2 study (NCT03288545) enrolled cisplatin-ineligible pts with MIBC (T2-T4aN0M0) and ECOG PS ≤2 who were eligible for RC+PLND. Pts received neoadjuvant EV (1.25 mg/kg) on Days 1 and 8 every 21 days for 3 cycles before undergoing RC+PLND. The primary endpoint was pCR rate (ypT0 and N0) by central pathology review. Key secondary endpoints included pDS rate (ypT0, ypTis, ypTa, ypT1, and N0), EFS based on investigator assessment, and safety. Results: 22 pts (median age 74.5 yr, range 56-81) were enrolled and treated; 17 pts (77.3%) remain on study. Pts had stage cT2 (68.2%), cT3 (27.3%), or cT4 (4.5%) disease. 68.2% of pts had transitional cell carcinoma only; 31.8% had a mixed histology. 86.4% of pts completed all 3 cycles of EV treatment; the median duration of EV treatment was 2.1 months (range 0.7-2.3). The pCR rate was 36.4% (95% CI, 17.2, 59.3) and the pDS rate was 50.0% (95% CI, 28.2, 71.8). Median EFS has not been reached. The EFS rate at 12 months was 76.4% (95% CI, 52.2, 89.4). All pts underwent surgery with no delays due to EV-related TEAEs. The most common EV-related TEAEs were fatigue (45.5%), dysgeusia (36.4%), and alopecia (31.8%); 18.2% of pts had grade ≥3 EV-related TEAEs. 68.2% of pts had surgery-related TEAEs and 31.8% pts had grade ≥3 surgery-related TEAEs. The most common surgery-related TEAEs were procedural pain (18.2%), anaemia (13.6%), and constipation (13.6%). 3 pts died due to AEs unrelated to EV treatment; in 2 pts the AEs occurred >30 days after RC+PLND. 36.4% of pts received subsequent cancer-related therapy. Conclusions: Neoadjuvant EV monotherapy treatment showed promising results for antitumor activity and EFS with a manageable safety profile in cisplatin-ineligible pts with MIBC. These results support ongoing phase 2 and 3 programs in MIBC evaluating EV alone or combined with pembrolizumab (EV-103 Cohort L, KN-905, KN-B15). Clinical trial information: NCT03288545 .