A Study to Evaluate TAR-210 Versus Single Agent Intravesical Cancer Treatment in Participants With Bladder Cancer

Inclusion Criteria:

• Main study only: Have a histologically confirmed diagnosis (within 90 days ofrandomization) of IR-NMIBC with at least one of the following criteria fulfilled: a.Ta low grade (LG)/ Grade 1 (G1): primary or recurrent, b. Ta LG/G2: primary orrecurrent and c. Greater than or equal to (>=) 1 of the following risk factors: i.Multiple Ta LG tumors, ii. Solitary LG tumor >= 3 cm, iii. Early recurrence (lessthan [<] 1 year), iv. Frequent recurrence (greater than [>] 1 per year), v.Recurrence after prior adjuvant intravesical treatment (single perioperative dose ofchemotherapy does not fulfill this risk factor)

• Substudy only: Have a histologically confirmed new diagnosis (within 90 days ofrandomization) of IR-NMIBC for whom MMC is deemed the therapy of choice according tolocal standard of care with at least 1 of the following criteria fulfilled: a. TaLG/G1, b. Ta LG/G2, and >=1 of the following risk factors: i) Multiple Ta LG tumors,ii) Solitary LG tumor >=3 cm

• Have a susceptible fibroblast growth factor receptor (FGFR) mutation or fusioneither by urine testing or tumor tissue testing (from TURBT tissue), as determinedby central or local testing

• Participants must be willing to undergo all study procedures (e.g., multiplecystoscopies from Screening through the end of study and TURBT for assessment ofrecurrence/progression) and receive the assigned treatment, including intravesicalchemotherapy if randomized into that arm.

• Visible papillary disease must be fully resected prior to randomization and absenceof disease must be documented at Screening cystoscopy

• Can have a prior or concurrent second malignancy (other than the disease understudy) which natural history or treatment is unlikely to interfere with any studyendpoints of safety or the efficacy of the study treatment

• Have an Eastern Cooperative Oncology Group performance status of 0 to 2

Exclusion Criteria:

• Known allergies, hypersensitivity, or intolerance to any study component or itsexcipients, including: a. Erdafitinib excipients; b.TAR-210 drug delivery systemconstituent materials ; c. urinary placement catheter materials; d. MMC orchemically related drugs; e. Gemcitabine or chemically related drugs

• Presence of any bladder or urethral anatomic feature (that is, urethral stricture)that, in the opinion of the investigator, may prevent the safe insertion, indwellinguse, removal of TAR-210 or passage of a urethral catheter for intravesicalchemotherapy

• Polyuria with recorded 24-hour urine volumes > 4000 milliliters (mL)

• Current indwelling urinary catheters, however, intermittent catheterization isacceptable

• Had major surgery or had significant traumatic injury and/or not fully recoveredwithin 4 weeks before first dose (TURBT is not considered major surgery)

Substudy:

• Previous diagnosis of histologically confirmed urothelial bladder carcinoma at any time prior to current qualifying diagnosis