The circular, sent out last September in a plain brown envelope, had in place of an address the words: "It doesn’t matter to me who you are."
A letter inside the envelope, ‘speaking’ as cancer in the first person, used reverse psychology to try to persuade potential donors to support the charity.
"Everyone knows me and they know the devastation I cause… I am cancer… every two minutes I take hold of another person… don’t donate to Cancer Research UK," the letter said.
In an adjudication published today, the ASA said it received four complaints from members of the public about the leaflet.
Three said the envelope and letter were threatening in tone or likely to cause distress to current or past cancer sufferers. Another said the circular was not clearly identifiable as marketing material.
The ASA upheld both reasons for the complaints under rules that say advertising must be identifiable as marketing material and which cover causing harm or offence.
"We considered that the appearance and content of this message was likely to be received as a threatening message and, when delivered directly to recipients’ homes, was likely to cause serious distress to some members of the public, particularly those who were vulnerable," the ruling says.
The ASA told CRUK that the advert must not appear again in its current form and that the organisation should avoid causing recipients "serious distress" with future marketing campaigns.
CRUK said it was sorry the leaflet upset people. "We’d like to take this opportunity to apologise to anyone who was upset by this mailing and reiterate that it was never our intention to cause distress," said a statement from Nick Georgiadis, head of direct giving at CRUK.
"The aim was to inspire people to fund our research by representing the anger some people feel toward this terrible disease. When the original mailing was sent out we listened carefully to what our supporters said about it – both positive and negative – and in November we decided not to use this appeal again in its current format."