cancel UIAlertView programmatically

How can I cancel a UIAlertView programmatically? This is the code that I use to show the UIAlertView

UIAlertView *myAlertView = [[UIAlertView alloc] initWithTitle:@"Save Background" message:@"Downloading..." delegate:self cancelButtonTitle:@"Cancel" otherButtonTitles:nil, nil];
    CGAffineTransform myTransform = CGAffineTransformMakeTranslation(0.0, 70.0);
    [myAlertView setTransform:myTransform];
    [myAlertView show];