Phase 2A/B Efficacy and Safety of Dabogratinib in Participants With Low Grade Upper Tract Urothelial Carcinoma

* Participants ≥ 18 years of age at the time of informed consent and willing and able to comply with all required study procedures * Confirmed LG UTUC (both favorable and unfavorable) per AUA * At least 5mm of marker lesion(s) left behind * Identification of marker lesion(s) within 8 weeks prior to randomization (refer to Inclusion Criterion #2) * If synchronous NMIBC, NMIBC must be fully resected and low-grade Ta or T1 * No prior BCG administration within 1 year of date of consent. * No intravesical chemotherapy within 8 weeks prior to C1D1 (including UGN-101). * No systemic chemotherapy within 3 months prior to C1D1 * ECOG PS 0-2 * Pathology consists of pure urothelial carcinoma * Adequate bone marrow function: i. Absolute neutrophil count (ANC) ≥1,500/mm3 ii. Platelet count ≥75,000/mm3 iii. Hemoglobin ≥10.0 g/dL * Adequate liver function: i. Total bilirubin ≤ ULN ii. Alanine aminotransferase (ALT) ≤ ULN iii. Aspartate aminotransferase (AST) ≤ ULN * Adequate renal function: i. Estimated glomerular filtration rate \>30 mL/min ii. Serum Phosphate level ≤ ULN prior to starting treatment iii. International normalized ratio (INR) ≤1.5 × ULN Exclusion Criteria: * Evidence or any features of high grade (HG) UTUC * History of carcinoma in situ (CIS) * History of prostatic urethral involvement * Current or previous history of muscle invasive bladder cancer * Current or previous history of lymph node positive and/or metastatic bladder cancer * Evidence of squamous cell carcinoma, adenocarcinoma or undifferentiated carcinoma or small cell of the bladder * Currently receiving systemic cancer therapy (cytotoxic or immunotherapy) * Current or prior history of pelvic external beam radiotherapy for bladder cancer * Current or history of receiving a prior FGFR inhibitor * Systemic immunotherapy within 6 months prior to C1D1 * Treatment with an investigational agent within 30 days or 5 half-lives from C1D1, whichever is shorter; compounds with an unknown half-life will be default to 30 days. * Prior treatment with an intravesical or intracavitary agent within 8 weeks of C1D1. * Current evidence of central serous retinopathy or retinal pigmented epithelial detachment of any grade at time of baseline examination. * Requiring use of medications that are strong and moderate inhibitors or inducers of CYP3A or inhibitors of P-gp and BCRP transporters (prohibited list of medications)