Herein, we report the case of a patient with metastatic UBC harboring a rare M1043I mutation of PIK3CA which was detected using DNA-based next-generation sequencing. The patient received everolimus as first-line therapy after palliative transurethral resection. The treatment resulted in complete response within 1 month, and the patient achieved a progression-free survival (PFS) of >6 months according to reports from the last follow-up visit.