My guess is that if you were using a "Cancel" button, it would be fore e-commerce purposes. Like "Cancel Order?" In that case, you can use a checkbox and then use the submit button. Or you can create your own button (image) and import it into Design Studio, drop it in and hyperlink.
To my knowledge, I don't believe there is an out of box "Cancel" button for use from Marketo if that's what you are referring to.