(HARBOR) Study to Evaluate Efficacy and Safety of BLU-263 Versus Placebo in Patients With Indolent Systemic Mastocytosis

To be able to join this study, you would generally need to be an adult (18 years or older) and have a confirmed diagnosis of indolent systemic mastocytosis (ISM) or smoldering systemic mastocytosis (SSM) by a specialist. For most parts of the study, you would need to have ISM and your current treatments for symptoms, such as allergy medicines or stomach protectors, shouldn't be fully controlling your symptoms. This means you still experience ongoing problems despite trying at least two different symptom-managing therapies.

Your general health also needs to be good enough to participate, meaning you should be able to carry out most daily activities without too much difficulty. If you are taking steroid medications for your symptoms, the dose needs to be stable and not too high. Your current symptom-managing medication regimen also needs to have been stable for at least two weeks before joining.

There are also reasons why you might not be able to join. For example, if your mastocytosis is a more severe type or if it's linked to other specific blood conditions, you wouldn't be eligible. You also can't have serious heart problems or have had certain types of cancer within the last three years. The study doctors will carefully check your medical history to make sure it's safe for you to take part.

If you decide to take part in this study, you will likely be involved for several months, possibly over a year, depending on which part of the study you join. Your involvement will typically include:

* **Initial health checks:** Before starting, you'll have various tests like blood tests, heart checks (ECG), and physical exams to ensure the study is safe and right for you. * **Taking the study medicine:** You'll receive either elenestinib or a placebo (a dummy pill) as prescribed, which you'll take at home. You'll continue taking your usual medicines for your symptoms as well. * **Regular clinic visits:** You'll have scheduled appointments at the study clinic throughout your participation. At these visits, doctors and nurses will monitor your health, check for any side effects, ask about your symptoms, and take blood samples. These visits help the study team understand how the medicine is working and ensure your safety. * **Follow-up:** After you stop taking the study medicine, you'll have some follow-up visits or calls to track your health and any lingering effects. * **Total duration:** The exact length of your participation will be explained by the study team, but it can range from several months to over a year, including the initial treatment period and follow-up.