Be aware that your code in the BackgroundWorker.DoWork event handler may finish its work as a cancellation request is being made, and your polling loop may miss BackgroundWorker.CancellationPending being set to true. In this case, the AsyncCompletedEventArgs.Cancelled flag of System.ComponentModel.RunWorkerCompletedEventArgs in your BackgroundWorker.RunWorkerCompleted event handler will not be set to true, even though a cancellation request was made. This situation is called a race condition and is a common concern in multithreaded programming. For more information about multithreading design issues, see Managed Threading Best Practices.