A man who ordered a Kindle e-book reader claims he received a tumor sample instead.

James Potten of Bristol, England, posted a photo of his partially opened package - meant for a hospital - on Twitter with the single-word caption: "wow."

A paper seal around the package reads: "Specimen return kit - Patient tumor specimen enclosed."

Plotten reached out to FedEx on Twitter but struggled to get them to collect the wrongly-delivered package.

"I've been trying to get FedEx to collect it as it is potentially a sample that needs to be tested and sent back with some urgency," Plotten told the BBC. "I don't know where my Kindle is, but if it is at [London's Royal Free Hospital] I'd be happy to do an exchange."

Plotten tweeted Sunday that the sample was "now on route to its rightful owner," and reported Monday he'd received his Kindle.

"Delivered!! Thanks finally to @fedex."

FedEx told the BBC they "regretted the error" and "will consider future changes to our processes."