The 50-year-old singer - who has previously battled breast cancer - claims no one will confirm usage of the device was what caused the tumour, but she feels like it might be behind it. She said: "There are no doctors that will confirm that. But I do have a theory that it`s possible that it`s related to that. I used to spend hours on the archaic old cell phones." Initially, Sheryl was concerned she had Alzheimer`s disease when she began forgetting song lyrics, but is glad the lump is not of serious worry. Speaking on `Katie` she said: "I was worried I had early onset Alzheimer`s. It`s nothing to worry about. But it was definitely a sobering moment." The `Soak Up The Sun` singer previously revealed it was memory loss which led her to get the problem checked out. She said: "I worried about my memory so much that I went and got an MRI. And I found out I have a brain tumour. "And I was, like, `See? I knew there was something wrong.` I haven`t really talked about it...But it`s benign, so I don`t have to worry about it. But it gives me a fit."