A Phase 1/2a Study of STM-416 Administered Intraoperatively to Patients Undergoing Transurethral Resection of Bladder Tumor (TURBT) for Recurrent High-Grade Papillary Bladder Cancer

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.