“How long do you have left?” and “my dog died of cancer” were among the remarks recorded by Teenage Cancer Trust.
Teens and young adults have shared their experiences with the charity for its What Not To Say campaign.
The trust is highlighting topics to avoid, including asking when someone is going to die, talking about relatives that died of cancer or speculating about how a person first developed the disease.
Maddy Elleby, 18, from Farnham, Surrey, was diagnosed with Hodgkin lymphoma two years ago.
She said some people were “so desperate to relate that they told me their dog had died of cancer, or their granny, or their cousin’s neighbour”.
Sophie Angell, 17, from Southwell, Notts, was diagnosed with leukaemia aged 13. She said: “At the start of my diagnosis, a friend made a comment about palm oil, saying that I got cancer because I had previously eaten Nutella.
“Looking back, it seems absurd, and it came from a lack of understanding. They didn’t know that childhood cancers are very rarely lifestyle-induced. Another time, a peer at school said that I got cancer because I didn’t believe in God. I felt blamed for something out of my control.”
Other no-go topics include talking about how a patient’s appearance has changed or whether they wear a wig, and telling young patients they are brave. A survey for the charity found saying nothing could also be hurtful, with 55% of young sufferers finding that some friends did not contact them as often after their diagnosis.
Amy Harding, director of services at Teenage Cancer Trust, said: “People can feel awkward talking about cancer and blurting out the wrong thing, but it’s so important to stay in touch.
“From simple things like staying connected by sending messages or asking someone if they want to talk, we shouldn’t underestimate how much the little things we say or do can make a difference to people going through a tough time.”