The 'Blank Space' singer shared the heartbreaking news with fans via a Tumblr post called 'Just so you know…'
Taylor wrote: "For Christmas this year, I asked my mum that one of her gifts to me be her going to the doctor to get screened for any health issues, just to ease some worries of mine. She agreed, and went in to get checked. There were no red flags and she felt perfectly fine, but she did it just to get me and my brother off her case about it.
"The results came in, and I'm saddened to tell you that my mum has been diagnosed with cancer. I'd like to keep the details of her condition and treatment plans private, but she wanted you to know."
Taylor said her mother wanted young fans to be aware of the disease and encourage their own parents to get checked.
"She wanted you to know because your parents may be too busy juggling everything they've got going on to go to the doctor, and maybe you reminding them to go get checked for cancer could possibly lead to an early diagnosis and an easier battle…
"Or peace of mind in knowing that they're healthy and there's nothing to worry about. She wanted you to know why she may not be at as many shows this tour. She's got an important battle to fight."
Taylor concluded her post: "Thank you for caring about my family so much that she would want me to share this information with you. I hope and pray that you never get news like this."