The blog by the Forever and Iggy's House author, who is based in New York, described her experience from the first diagnosis in June through her decision to get a mastectomy.
Blume, whose books have been translated into 31 different languages, reflected on the disbelief she felt after hearing the news from her doctor.
“Wait — me? There’s no breast cancer in my family [recent extensive genetic testing shows no genetic connection]. I haven’t eaten red meat in more than 30 years. I’ve never smoked, I exercise every day, forget alcohol — it’s bad for my reflux — I’ve been the same weight my whole adult life. How is this possible? Well, guess what – it’s possible,” she wrote.
Blume even joked about the size of her breasts, with a reference to one of her most beloved works Are You There God? It's Me, Margaret.
"A-cups? The breast surgeon asked at our first meeting. She nailed it. I told her the exercises didn't work for me. Not sure she got my attempt at a joke," she said.
Blume, 74, said it is now a month since her surgery and she is feeling stronger every day, walking and going out occasionally with husband George.
“My friends who've had breast cancer have been so helpful and supportive I can never thank them enough. They got me through this. They were my inspiration,” she wrote.
Blume concluded her blog entry by offering words of encouragement for those battling cancer.
“When it comes to breast cancer you’re not alone, and scary though it is, there’s a network of amazing women to help you through it.”