example.cs

var leave = false;

while (someCondition && !leave)
{
    System.Threading.Thread.Sleep(500);

    Application.Current.Dispatcher.Invoke(new Action(() =>
    {
        if (someOtherCondition)
        {
            // Do stuff...
        }
        else
        {
            if (anotherCondition)
            {
                leave = true;
            }

            // Do something else...
        }
    }));
}