Possible Relapse

2 years ago we found out my 13 year old son had Burkitt's Lymphoma. It was such a devastating blow. You never expect to hear news like that about your child. After 5 months of chemotherapy it was gone and the recovery process began. His hair grew back, he went back to school, life returned to normal. A year and a half later he went to his 6 month checkup, and the doctor's expressed concern about a "mass" in his liver. All of a sudden, all of the fear and anxiety I felt the first time he was diagnosed came flooding back. He has a PET scan tomorrow to identify this "mass", but of course I can't help but to fear the worst. Since the liver isn't part of the lymphatic system, I'm assuming that if it is a tumor then the cancer has already mestastisized? As much as I understand the treatment plan and all of the processes, the fear of not knowing what that PET scan will reveal is overwhelming. I was feeling so lucky to have a healthy son again and then just seems to come out of nowhere. I'm wondering if there are any other parents out there who have experienced this? Did living through the first treatment help you cope with the possible relapse or did it hit you just as hard as it is hiting me? It seems like everything that I learned from his treatment is only feeding my fears that this a relapse.