My husband has MGUS and amyloidosis and received treatments and then a stem cell transplant in July 2022. His calcium went up a bit and so they did the PTHrP as well. It was elevated. They then did a PETscan and found nothing. They repeated the PRHrP and like you it was even higher. The oncologist he sees is not wanting to 'chase the lab value', but like you we are concerned for this positive marker for cancer after what he has been through. We see the oncologist again soon and I'll let you know if we hear anything new. They are doing a urine cytology and may do a prostate MRI because the regular PET scan he had may not show these cancers in these areas. That's according to a second opinion we got from hematology/oncology dr that he has seen before. Good luck to you. You are so right how frustrating it can be not to know what's going on.