The main purpose of this study is to compare the disease-free survival between participants receiving treatment with TAR-210 versus investigator's choice of intravesical chemotherapy for treatment of intermediate-risk NMIBC.

Inclusion Criteria:

• Main study only: Have a histologically confirmed diagnosis (within 90 days of randomization) 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 or recurrent 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 (less than [<] 1 year), iv. Frequent recurrence (greater than [>] 1 per year), v. Recurrence after prior adjuvant intravesical treatment (single perioperative dose of chemotherapy does not fulfill this risk factor)
• Substudy only: Have a histologically confirmed new diagnosis (within 90 days of randomization) of IR-NMIBC for whom MMC is deemed the therapy of choice according to local standard of care with at least 1 of the following criteria fulfilled: a. Ta LG/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 fusion either by urine testing or tumor tissue testing (from TURBT tissue), as determined by central or local testing
• Participants must be willing to undergo all study procedures (e.g., multiple cystoscopies from Screening through the end of study and TURBT for assessment of recurrence/progression) and receive the assigned treatment, including intravesical chemotherapy if randomized into that arm.
• Visible papillary disease must be fully resected prior to randomization and absence of disease must be documented at Screening cystoscopy
• Can have a prior or concurrent second malignancy (other than the disease under study) which natural history or treatment is unlikely to interfere with any study endpoints 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 its excipients, including: a. Erdafitinib excipients; b.TAR-210 drug delivery system constituent materials ; c. urinary placement catheter materials; d. MMC or chemically 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, indwelling use, removal of TAR-210 or passage of a urethral catheter for intravesical chemotherapy
• Polyuria with recorded 24-hour urine volumes > 4000 milliliters (mL)
• Current indwelling urinary catheters, however, intermittent catheterization is acceptable
• Had major surgery or had significant traumatic injury and/or not fully recovered within 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

The data sharing policy of Johnson & Johnson Innovative Medicine is available at www.innovativemedicine.jnj.com/our-innovation/clinical-trials/transparency. As noted on this site, requests for access to the study data can be submitted through Yale Open Data Access (YODA) Project site at yoda.yale.edu.