Cheryl offered her support after Sarah Harding confirmed she was writing a book during her cancer treatment.
The Girls Aloud singer announced in August that she is battling breast cancer, which has advanced around her body.
Sharing an update on her health on Instagram, the 39-year-old said she has been penning her life story, Hear Me Out, while undergoing treatment.
Bandmate Cheryl publicly urged people to pre-order her offering, sharing Sarah’s news on her own story.
‘Well this is going to be an interesting read,’ the mum-of-one commented.
‘Love you @Sarahnicoleharding. Swipe up to pre-order.’
‘So proud of you for delivering this.’
Nadine Coyle commented: ‘Love you!!! Xx,’ while Kimberley Walsh added: ‘So proud of you.’
Sarah revealed her cancer diagnosis in August, explaining that she was told of the news earlier this year.
‘A couple of weeks ago I received the devastating news that the cancer has advanced to other parts of my body,’ she tweeted at the time.
‘I’m currently undergoing weekly chemotherapy sessions and I am fighting as hard as I possibly can. I understand this might be shocking to read on social media and that really isn’t my intention.
‘But last week it was mentioned online that I had been seen in hospital, so I feel now is the time to let people know what’s going on and this is the best way I can think of to do so.
‘I am doing my very best to keep positive and will keep you updated here with how I’m getting on.’
Offering an update on Thursday, the Celebrity Big Brother star said she had been using the time to focus on writing her life story.
Stating that she was ‘fighting as hard as possible’, she added: ‘In September the lovely people at Ebury Publishing asked me if I’d be interested in writing a book about my life story.
‘It came at such a good time as it’s given me something fun & positive to focus on while I’ve been stuck at home in between trips to the hospital for treatment.
‘I’ve nearly finished it now and this week Mum and I have been looking though old photos, choosing which ones to include. It’ll be out after Christmas and I’m really proud of it.
‘I hope you’ll like it. Sending lots of love to everyone – I hope you’re all keeping well.’