The Girls Aloud star revealed her diagnosis via Instagram in September, before dialling back on her social media life.
She returned to Instagram on Monday to update fans and friends.
“I know I’m not really that present on here which I promise I’ll try to get a bit better at, as honestly it means the world to me when I come on and see all your well wishes,” Harding wrote.
“Thank you for the love and support, on bad days it helps me so much,” she went on.
“So here’s a little update from me… Mum, the dogs and I had a really lovely but quiet Christmas together, which was different to my usual, but seemed a fitting way to end such a strange year. And since then, in between treatments and hospital visits I’ve managed to finish my book!” the singer and TV personality shared.
“I’m so excited for it to come out. I can’t rewrite history; all I can do is be honest and wear my heart on my sleeve,” she reflected, adding: “it’s really the only way I know. I want to show people the real me.”
Harding also confirmed the title of her autobiography – Hear Me Out – explaining: “It’s the title of the song I wrote on the second Girls Aloud album and I’ve always really loved it.”
She noted: “The lyrics have always meant a lot to me. It’s been lovely revisiting our songs, looking back over photos and writing down memories from my last 39 years. I really hope you might enjoy reading about them too.”