That's a #darkpattern , cancer.org: after I #donate I follow the Unsubscribe link from the receipt email, only to get a 404 error . Grr. #integrity is job 1. And nothing says lack of integrity to a web guy like a 404.
At least the 404 page suggested a search, which led me to a straightforward unsubscribe form.
I'm still glad I donated. Someone close to me had their skin cancer found early enough that one procedure was enough to treat it.