MVP design pattern question

Hi experts,

I have events that get fired from my View and get handled in my Presenter
for example i might have in my View:
            this.radioButtonList.SelectedIndexChanged += delegate
            {
                OnClassSelected(this.radioButton, EventArgs.Empty);
            };
and OnClassSelected gets handled in my presenter:
void _view_OnClassSelected(object sender, EventArgs)
{
{

My problem is how can i use the sender parameter to for example get the selected value if I don't have access to System.Web.UI.WebControls to cast the sender object to a RadioButtonList?

Thanks