This is a first-in-human (FIH), Phase 1/2a, multi center, open-label, single treatment, dose escalation and expansion study designed to determine the safety and tolerability of STM-416 in patients with bladder cancer.

This is a 2-part, multicenter, first-in-human (FIH), Phase 1/2a study in patients with a history of pathologically confirmed high-grade Ta or T1 NMIBC without CIS who have completed SOC previously, with recurrent papillary disease seen on cystoscopy, and who are undergoing TURBT without perioperative intravesical chemotherapy. All patients will receive relevant SOC therapy following TURBT. SOC will be administered in the adjuvant setting.

Phase 1 is an open-label, single-treatment, dose-escalation study to evaluate the safety and tolerability of up to 6 increasing doses of intraoperatively administered STM-416 utilizing a 3+3 convention, with 3 to 6 patients enrolled in each STM-416 dose level, with a minimum of 6 patients enrolled at the highest dose level, for a total of approximately 30 patients.

Phase 2a is a randomized, single-blind, single-treatment, dose-expansion study that will comprise 2 arms: TURBT + STM-416 Dose 1 followed by SOC versus TURBT + STM-416 Dose 2 followed by SOC.

Inclusion Criteria:

1. Are aged 18 years or older;

2. Have a history of pathologically confirmed high-grade Ta or T1 NMIBC without CIS who have completed SOC previously, with recurrent papillary disease seen on cystoscopy, and who are undergoing TURBT without perioperative intravesical chemotherapy;

3. Are considered high risk for recurrence;

4. Have Eastern Cooperative Oncology Group (ECOG) Performance Status of 0, 1, or 2;

5. Have adequate organ and marrow function as defined below:

   • Hemoglobin 9.0 g/dL;
   • Absolute neutrophil count 1.5 × 109/L (1500 per mm3);
   • Platelet count 75 × 109/L (75,000 per mm3);
   • Serum bilirubin 1.5 × institutional upper limit of normal (ULN);
   • AST (serum glutamic-oxaloacetic transaminase)/ALT (serum glutamic-pyruvic transaminase) 2.5 × institutional ULN; and
   • Creatinine CL 60 mL/min by the Cockcroft-Gault formula or by 24-hour urine collection for determination of creatinine CL: Males: Creatinine CL (mL/min) = Weight (kg) × (140 - Age)/72 × serum creatinine (mg/dL); or Females: Creatinine CL (mL/min) = Weight (kg) × (140 - Age) × 0.85/72 × serum creatinine (mg/dL).

Exclusion Criteria:

1. Have a history of CIS or MIBC;

2. Are receiving any other investigational agents;

3. Have a history of allergic reactions attributed to compounds of similar chemical or biologic composition to resiquimod (R848), or excipients used in STM-416 including poloxamer 407 and sodium hyaluronate;

4. Have an uncontrolled intercurrent illness including, but not limited to, ongoing or active infection, symptomatic congestive heart failure, unstable angina pectoris, cardiac arrhythmia, or psychiatric illness/social situations that would limit compliance with study requirements.

   Urinary tract infections are not exclusionary unless they are NCI-CTCAE Grade 3 or higher;

5. Are a woman of childbearing potential regardless of contraceptive use; Note: Women of childbearing potential are only to be excluded in Phase 1 and Phase 2a to avoid bias due to the low prevalence of NMIBC in this population. However, they will be included in subsequent Phase 2/3 studies.

Women of childbearing potential are only to be excluded in Phase 1 and Phase 2a to avoid bias due to the low prevalence of NMIBC in this population.