The 82-year-old TV presenter was unable to appear in person on the live BBC programme to celebrate the 50th anniversary of magazine show That's Life!, which she fronted from 1973 to 1994.
Rantzen sent a statement which was read out by The One show presenter Alex Jones.
She said: "I can’t believe it’s 50 years since the launch when I’m still only 35 myself. Those 21 years of That’s Life! passed in a flash!
50 years have flown by since the launch of 'That’s Life'! We have a lovely message from Dame Esther Rantzen to celebrate the milestone ❤️ #TheOneShow 👉 https://t.co/e02dA5i3uS pic.twitter.com/SJKTZO90kw
— BBC The One Show (@BBCTheOneShow) May 23, 2023
"My current illness, lung cancer, is the reason that, sadly, I can’t be with you tonight – I would have loved to join you to suggest that someone should be making That’s Life! today.
"Of course, The One Show does a lot of the same great work, but you do need a few more talented dogs.
"I would also have loved to be there to thank you so much for reviving all those happy memories – please send everyone, the viewers and my fellow That’s Lifers, my fondest love."
Rantzen – founder of charities Childline and The Silver Line – announced in January that she had been diagnosed with lung cancer, which had spread, but added that she remained "optimistic" as she underwent treatment.
She said: "In the last few weeks I have discovered that I am suffering from lung cancer which has now spread.
"At the age of 82, this diagnosis has prompted me to look back over the years, and I want to express my profound thanks to everyone who has made my life so joyful, filled with fun, and with inspiration.
"I have been continuously inspired by the courageous children, older people and viewers who have trusted me with their life stories. I have always tried to live up to that trust.
"As I am sure you will understand, while I am awaiting the results of the tests, I am unable to answer questions.
"Thanks to the extraordinary skills of the medical profession there are wonderful new treatments, so I am remaining optimistic."
Rantzen was a writer and producer as well as the host of consumer affairs show Thats Life! which aired on BBC One for 21 years.
It covered a range of topics, from lighthearted items such as a 'talking' dog who could say 'sausages', to serious subjects such as scams, public safety and child abuse.
A helpline set up after an item on child abuse inspired Rantzen to launch children's charity Childline in 1986.
In 2013 she launched The Silver Line, offering help and support for the over-55s.
Rantzen's husband Desmond Wilcox died in 2000. She has three children, Miriam, Rebecca and Joshua.
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