PET Scan found Soft Glow in Liver (Golf Ball Size)

sunshine2022

I am asking for my mother. Are the glows on the PET Scan always cancer? They want to follow up with an MRI to get a better picture and if that's not clear a biopsy. They found one soft glowing golf ball size in her liver. I thought PET Scans were the best.

(Background)She started with Kidney cancer years ago and had one removed, then a year later it embedded in her spine. She has complications from that surgery but the cancer went into remission and she has been doing immunotherapy ever since. She did radiation at first but that just destroyed the bones and skin underneath.