Soft Tissue Mass found on CT

Bookworm14

I just had my CT scan to make sure there was non metastasis. The radiologist mentioned a soft tissue mass that is 12mmx12mm in the superior anterior mediastinum. He says remains unchanged from last Pet/Ct scan ( never mentioned in report). In my original PET (2018) at diagnosis, my sternum had FDG uptake, but they could not see anything to correlate to. They seemed to not be very concern as the treatment would be the same they said. My question is what could this be? The radiologist mentioned possibly lymph node and less likely a teratoma or Hamartomas. Has anyone had something similar