This is a phase 3, multicenter, randomized, placebo-controlled, double-blind study of treatment with brepocitinib (TYK2/JAK1 inhibitor) in adults with dermatomyositis (DM). The primary objective of this study is to assess the efficacy of two dose levels of brepocitinib in comparison to placebo, as measured by differences in the Total Improvement Score (TIS). After 52 weeks of double-blind treatment, participants have the option to continue therapy in a 52 week open-label extension phase where all participants will receive brepocitinib.

Inclusion Criteria:

• A diagnosis of dermatomyositis according to 2017 EULAR/ACR Classification Criteria for Idiopathic Inflammatory Myopathies
• Adult subjects (18-75 years old)
• Active muscle and skin disease at screening and baseline
• Prior therapy OR current therapy with corticosteroids, hydroxychloroquine, and/or one non-steroid immunosuppressant
• Weight > 40 kg to < 130 kg, and with a body mass index (BMI) < 40 kg/m2.

Exclusion Criteria:

• Dermatomyositis with end-stage organ involvement

• Dermatomyositis with irreversible muscle involvement

• History of:

  • Any lymphoproliferative disorder
  • Active malignancy;
  • History of cancer within 5 years prior to randomization (exceptions for basal cell carcinoma, squamous cell carcinoma, ductal carcinoma in situ of the breast, carcinoma in situ of the uterine cervix, or thyroid carcinoma.)
  • Cancer-associated dermatomyositis

• Overlap myositis/connective tissue disease (except for overlap with Sjögren's syndrome)

• Participants at a risk of thrombosis or cardiovascular disease

• Participants with a high risk for herpes zoster reactivation

• Participants with active or recent infections

Priovant Therapeutics will provide access to individual de-identified participant data and related study documents (e.g. protocol, Statistical Analysis Plan (SAP), Clinical Study Report (CSR)) from eligible studies upon request from qualified researchers, and subject to certain criteria, conditions, and exceptions. Data requests will be reviewed and approved on the basis of scientific merit.

The data will be made available within 24 months after study completion and will be accessible for a time frame appropriate for the approved proposal.

Access will be provided following review and approval of a research proposal and execution of a Data Sharing Agreement (DSA). Further details on Priovant Therapeutics' data sharing criteria and process for requesting access can be obtained by emailing info@priovanttx.com.