Study Overview: This study is testing a medicine called etrasimod to see if it helps teenagers with a bowel disease called ulcerative colitis (UC). UC causes swelling and sores in the colon. The study will last 52 weeks, but participants can continue for up to 4 more years if needed.

Key Points:

• The study lasts for 52 weeks, with a chance to join a longer period of up to 4 years.
• Participants must have moderately to severely active ulcerative colitis.
• People with other similar diseases, like Crohn's disease, cannot join.

Details: The study will check if etrasimod is safe and works well in treating UC. It will also study how the body processes the drug, known as pharmacokinetics (PK). Participants can continue their current UC treatments if they are already taking them. However, those with very severe forms of the disease or other similar conditions cannot join. If the study goes well, participants might help get the drug approved for everyone.