C# Access check boxes within combobox dropdown

So I'm currently trying to access check box items held as a collection within a combo box. My problem is, when I go to set:

var dropGenre = Drop_Genre.Items;

and change the position each run through a loop, I cant seem to access anything "check box like" at any point. I'm trying to see which items in the drop down are "checked" and return the name of those items.

I tried looking through the windows documentation but didn't have any luck finding out about check boxes within combo boxes; in fact most sources I checked were asking if it was even possible and didn't seem to reference this functionality at all. Thanks, sorry if this is poor formatting, first time asking something on here.