Noel Edmonds has suggested that a cancer sufferer's ill health is caused by his "negative attitude".
The TV presenter is a user of the EMPpad, a machine which aims to stimulate "cellular resonance" in the body.
Praising the machine, he tweeted: "A simple box that slows ageing, reduces pain, lifts depression and stress and tackles cancer. Yep tackles cancer!"
But he did not take kindly to criticism from @VaunEarl, whose Twitter biography states he has kidney cancer, lymph node metastases and psoriatic arthritis.
@VaunEarl wrote: "This sort of quackery should be illegal if it isn't already," adding: "I think Noel Edmonds should stick to what he's good at. Presenting quiz shows and beard trimming, rather than curing cancer."
Edmonds fired back: "Scientific fact-disease is caused by negative energy. Is it possible your ill health is caused by your negative attitude? #explore".
Deal Or No Deal presenter Edmonds is a long-time fan of the device and has previously called it a "miracle pad", frequently recommending it to his followers.
He has said it can improve sleep, bring better health, reduce stress and even have an anti-ageing effect.
The TV presenter also claimed on Twitter that since he has started using the EMPpad he has been forced to cut his hair once a week.
EMPpad Limited said it does not pay Edmonds to advertise the product.
@VaunEarl's full name appears to be Vaun Earl Norman, and he also runs a blog titled My Adventures in Cancerland.
He replied to Edmonds: "Wow! How do you know I have a negative attitude. You have no idea who I am. #patronising #cancer... I'm the most positive person I know despite my disabilities and long term ill health. Weird."
He added: "Don't get me wrong I like Noel Edmonds, brilliant TV man. But much rather consult my Oncologist with 15 years experience than Mr Edmonds.
"I don't even mind Noel Edmonds using and offering 'positivity' tools. But cancer cures is a step too far."
EMPpad Limited company director Maria Robertson has previously worked as an assistant to Edmonds.
In the acknowledgements section of his book Positively Happy, he wrote: "To Maria Robertson - heartfelt thanks and enduring gratitude for your support, commitment and love beyond the call of duty."
EMPpad director Samuel Maddock said his company does not make the claim that its products prevent cancer.
He said: "Although research using very low frequency and intensity PEMF to help address cancer has produced some promising early results, it is currently in the very early stages and EMPpad does not make the claim that PEMF therapy can prevent cancer."
On how the products work, he said: "The EMPpad Omnium1 and EMPpad iMRS use very low intensity and frequency pulsed electromagnetic fields (PEMF) which target the cells within the body and help to improve the way they function.
"Research has demonstrated that this can lead to widespread health benefits, including supporting an effective immune response and a healthy overall body."
Professor Jane Maher, joint chief medical officer of Macmillan Cancer Support, said: "Cancer and its treatment can be a very scary experience, making some people feel helpless and too tired to be positive, but that does not mean they can't also survive their disease.
"Some patients tell us that having a positive attitude helps them when coping but we also know that a positive attitude means different things to different people and there should be no pressure on anyone to feel or act in a certain way.
"If you are feeling anxious or depressed, you don't have to go through it alone. It's really important that you do talk to your doctor, nurse or someone close to you about your feelings.
"There's also an army of people within the cancer community, including Macmillan, who can help with emotional support. We're available to talk on the phone or online when you need us."
Copyright (c) Press Association Ltd. 2016, All Rights Reserved. Picture (c) Tim Ireland / PA Wire.