CA 19-9 high but no malignancy

Hello,

My mom (75 years old) was diagnosed with pancreatic cancer early last year. She had surgery to remove her spleen and half of her pancreas. She later went through six months of chemo which she barely got through. After completing treatment her scans came back clean however, her oncologist told us that her CA 19–9 levels are trending up. At that time they around around 100. Over the course of the next nine months or so she had several CT scans as well as pet scans. She also had signatera tests done which were all negative. However, her CA 19-9 levels continued upwards. Her most recent CA 19-9 came back extremely high at 22000, before that it was 3800 and prior to that around 600-700. She had a petscan done and it did show new FDG activity in her pancreas around her surgical area. Her doctor did a EUS and the biopsy came back NON malignant. Her overall health has been great and continues to be, she walks 1-2 miles daily, is full of energy and she even recently kicked diabetes due to her diet and lifestyle change and has an a1c at 5.3. We just saw her doctor today and were told that even though The biopsy came back non-malignant she wanted to do chemo and radiation therapy. We are getting a second opinion next week but wanted to see if anyone has any thoughts on this. My understanding from all research is that CA 19–9 cannot be used as an official diagnosis and scans need to show proof. We’re concerned about jumping back into treatment as it didn’t go well the last time and given the fact that she feels great now, she feels very hesitant.
Thank you!