FedEx, which collected the tumour sample from Mr Potten said that it 'regretted the error' and 'will consider future changes to our processes'.
In a bizzare incident, a sample from a California cancer patient's tumour was mistakenly delivered to a man in the UK who had ordered a Kindle electronic book reader.
James Potten, 37, after opening the FedEx package discovered a box marked "patient tumor - specimen enclosed".
Mr Potten received a parcel from an address in California which was supposed to go to the Royal Free Hospital in London.
"When I opened it I had quite a shock," Mr Potten, an environmental consultant was quoted as saying by the BBC.
"My name was on the outside, but the contents weren't what I expected. I haven't opened the sealed box, which says exempt patient tissue, as it doesn't belong to me. The tracking code on the item had the same first five and last three numbers as my order but it wasn't my Kindle.
"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. I don't know where my Kindle is, but if it is at the Royal Free I'd be happy to do an exchange," he said.
The Royal Free Hospital said it was aware that a package "intended for one of its institutions... was delivered to an address in Bristol".
"We will await answers from the delivery company as to how this mistake was made," it said.
FedEx, which collected the tumour sample from Mr Potten said that it "regretted the error" and "will consider future changes to our processes".
The company later contacted me to say it had tried to deliver the package, but I was not at home, Mr Potten added.