Jane has raised more than �1.25m for charity

The 42-year-old Leeds mother of three said she would never have contemplated her latest challenge if she had realised how unwell she would be.

She now faces cycling 1,600 miles in 25 days to complete the trip from San Francisco to New York by September.

She said she would stop immediately if it was obvious that could not happen.

Mrs Tomlinson said: "If I'd known when we were planning the ride that I'd have been this unwell with my disease I wouldn't have even contemplated it."

People commit their time and money it's important to give it everything you can and that's just what I'm doing Jane Tomlinson

She described the ride - in which she has climbed more than 100,000ft and endured the effects of altitude sickness - as a "hideous torture".

"But once a decision is made to do it, people commit their time and money it's important to give it everything you can and that's just what I'm doing," she said.

"I just hope that going through this amount of discomfort then others don't have to go through the same whether they be cancer patients or children suffering chronic diseases.

"It's important that we found both cures to the diseases but constantly improve the palliative care of those afflicted."

'Give everything'

But Mrs Tomlinson, who is being followed in a support vehicle by her husband Mike, 45, and nine-year-old son Steven, said she was determined to continue.

"I am happy, cheerful and would be really enjoying the cycling if I wasn't in so much discomfort. I'll give it everything I can to complete the ride."

During the last 10 days, she has covered about 630 miles across the High and Low plains of Eastern Colorado and Kansas and is now in Missouri.

Mrs Tomlinson and her co-riders - Leeds Metropolitan University lecturer Ryan Bowd, 27, of Calgary, Canada, and 40-year-old Martyn Hollingworth, of Aviemore, in the Scottish Highlands - hope to reach St Louis by Friday if they are to arrive in New York by 1 September.

Jane is continuing to lose weight and it's causing a major headache trying to ensure that she gets enough nutrition down to ensure that she can continue Mike Tomlinson

Mr Tomlinson said: "The winds have been horrendous and her body has been buffeted every day except Friday.

"Last week became a gruelling battle of survival and it's fair to say that on at least two occasions it was a close call on whether it was too dangerous to continue."

He went on: "These last 10 days have been extremely fatiguing and the cumulative effects of over five weeks cycling are taking their toll.

"Jane is continuing to lose weight and it's causing a major headache trying to ensure that she gets enough nutrition down to ensure that she can continue."

Since being diagnosed with advanced metastatic breast cancer, Mrs Tomlinson has become the only cancer patient to complete a full Ironman triathlon and the first person to run a marathon while on chemotherapy.

She has also completed a 2,500-mile bike ride, from Rome to home, as well as a number of triathlons and other challenges.