Cornish people are among thousands sent hoax emails suggesting they have cancer.
The messages that look like they are from the National Institute for Health and Care Excellence (NICE) is suspected to be a scam.
It says the contents are likely to be distressing and has reported the hoax to the police.
Sir Andrew Dillon, the chief executive of NICE, said: "A spam email purporting to come from NICE is being sent to members of the public regarding cancer test results.
"This email is likely to cause distress to recipients since it advises that 'test results' indicate they may have cancer.
"This malicious email is not from NICE and we are currently investigating its origin. We take this matter very seriously and have reported it to the police."
NICE adds: "Please be assured that this email is not from NICE and we are currently investigating its origin. If you have received the email, do not open the attachments."