I have a known bone tumor it was found in a MRI. .. I had a bone scan done and the tumor showed up HOT. .. does that mean it's malignant? Would a. Benign tumor ever show up hot in bone scan. .. everything I read online says benign would show up cold

Possibly. A bone scan is a very sensitive test but it is not very specific. It will simply "light up" anywhere there is increased bone activity. Fractures, infection, cancers, and benign bone processes can light up on a bone scan. Osteoid Osteoma and Paget's disease are just two examples of benign processes that can light up on a bone scan. Discuss with your doctor, if any question, may need biopsy.