Olivia Newton-John says she has her good days and her bad days as she once again battles cancer.In an interview with "Today's" Hoda Kotb, which aired Wednesday, the singer talked about living with stage 4 metastatic breast cancer.She said these days she's "feeling pretty good.""I have my days, I have my pains," Newton-John said. "But the cannabis that my husband grows for me has been such a huge part of my healing, and so I'm a really lucky person."The "Grease" star was first diagnosed with cancer almost 30 years ago. She was treated for it and it returned in 2017.She and Kotb shared an emotional moment after the "Today" co-host shared that she too is a cancer survivor."We're sisters," Newton-John said. "Anyone that has gone on this journey with cancer, it's unknown destinations and surprises and turns."