A Study to Understand How the Study Medicine (PF-06823859) Works in People With Active Idiopathic Inflammatory Myopathies [Dermatomyositis (DM) and Polymyositis (PM)]

To be considered for this study, you need to be an adult, aged 18 or over, and have been diagnosed with active dermatomyositis (DM) or polymyositis (PM). You should also be taking a steady dose of a common anti-inflammatory medicine (like a corticosteroid) or another type of medicine that calms your immune system, or both.

There are also some reasons why you might not be able to join. For example, if your muscle weakness is due to a different condition, or if you have certain other serious health issues like some cancers, severe infections, or other significant diseases that could make the study medicine unsafe for you. We also can't include people who have had certain organ transplants or serious heart or brain conditions recently.

If you join this study, it will last for about 13 months. During this time, you will have 15 visits to the study centre. At these visits, you will receive either the study medicine (dazukibart) or a placebo (a dummy medicine with no active ingredients). Both will be given through a drip into your vein (an IV infusion), which takes about an hour, and this will happen every four weeks for 48 weeks.

Throughout the study, the research team will regularly check your health, symptoms, and how you are responding to the treatment. This will involve physical exams, blood tests, and asking questions about how you are feeling. All these checks are done to monitor your safety and see how the medicine is working.