The purpose of this open-label extension (OLE) study is to evaluate the safety and efficacy of etrasimod in participants with moderately to severely active ulcerative colitis (UC) who previously received double-blind treatment (either etrasimod 2 mg per day or placebo) during participation in one of the qualified Phase 3 or Phase 2 double-blind, placebo-controlled parent studies including but not limited to: (APD334-301 [NCT03945188] or APD334-302 [NCT03996369] or APD334-210 [NCT04607837]).

Inclusion Criteria:

• Must have met the eligibility criteria and have been enrolled in the qualified Phase 2 or 3 parent studies listed below or other qualified region-specific studies and meet the following additional criteria:

  1. Participants previously enrolled in Study APD334-301 (NCT03945188) or APD334-210 (NCT04607837) must have completed the Week 12 visit and have been assessed to have active UC that has not improved or has worsened from baseline or completed the Week 52 visit
  2. Participants previously enrolled in APD334-302 (NCT03996369) must have completed the Week 12 visit

Exclusion Criteria:

• If Investigator considers the participant to be unsuitable for any reason to participate in the Open-Label Extension study
• Experienced an adverse event that led to discontinuation from parent study

Pfizer will provide access to individual de-identified participant data and related study documents (e.g. protocol, Statistical Analysis Plan (SAP), Clinical Study Report (CSR)) upon request from qualified researchers, and subject to certain criteria, conditions, and exceptions. Further details on Pfizer's data sharing criteria and process for requesting access can be found at: https://www.pfizer.com/science/clinical\_trials/trial\_data\_and\_results/data\_requests.