Risankizumab for Refractory Perianal Fistulizing Crohn's Disease

Inclusion Criteria: 1. 15 years of age or older 2. Patients with an MRI-confirmed perianal fistula due to Crohn's disease 3. Patients with a draining anal fistula (maximum of 2 internal openings and maximum of 3 external openings) persisting for at least 2 weeks 4. Patients who have experienced inadequate response, diminished response, or intolerance to one or more of the following treatments in the past: ① Antibiotics (ciprofloxacin or metronidazole): Treatment lasting one month or longer. ② Immunomodulators (azathioprine, 6-mercaptopurine, or methotrexate): Treatment for 3 months or longer. ③ Advanced therapies (infliximab, adalimumab, vedolizumab, ustekinumab, and upadacitinib): Standard therapy administered for 14 weeks or longer as induction or maintenance therapy. 5. Patients who can agree to removal of the perianal seton by week 20 (week 20 ± 1 week) of administration, if patients already have setons inserted. 6. Patients with draining fistulas that were drained at least 6 weeks prior to enrollment. 7. Patients who have received a sufficient explanation regarding participation in this study, understood it fully, and provided their voluntary written consent, or patients whose legal representative received a sufficient explanation regarding participation in this study, understood it fully, and provided their voluntary written assent, if participating hospital/clinic requires. Exclusion Criteria: 1. Patients with a rectovaginal fistula at baseline (excluding past rectovaginal fistulas) 2. Patients with severe rectal and/or anal stricture and/or severe proctitis (defined as the presence of large ulcers exceeding 0.5 cm in the rectum) 3. Patients with abscesses or fluid collections exceeding 2 cm 4. Patients for whom MRI is contraindicated 5. Patients with a history of risankizumab, mirikizumab, or guselkumab administration 6. Patients who are refractory to three or more prior lines of advanced therapy 7. Patients who are intolerant to two or more prior lines of advanced therapy 8. Patients previously treated with darvadstrocel 9. Patients with a colostomy or ileostomy 10. Patients with disease activity (CDAI) \> 400 11. Patients receiving systemic steroids 12. Patients requiring new treatment with immunomodulators or advanced therapies during the screening period 13. Patients undergoing cytapheresis 14. Patients with a history of malignancy (excluding carcinoma in situ) 15. Patients with concomitant uncontrolled liver disease, hematologic disease, gastrointestinal disease (excluding Crohn's disease), endocrine disease, pulmonary disease, cardiac disease, neurological disease, psychiatric disease, brain disease, or active infection 16. Patients who underwent major surgery or suffered severe trauma within the past 6 months 17. Patients who are breastfeeding, pregnant, or may be pregnant, or who plan to become pregnant during the study period 18. Patients who showed persistent positivity for HBsAg and HBV-PCR, or seropositivity for HCV and quantitative HCV-PCR within 6 months prior to the start of the screening period 19. Patients who received a live vaccine within 4 weeks prior to the start of risankizumab administration 20. Patients with active tuberculosis 21. Other patients deemed inappropriate for trial participation by the principal/ sub-investigator responsible