Had my CEA levels been high on this test, combined with the CT scan result, that would have been fairly conclusive evidence this is a tumor. However, the converse is not necessarily true. This doesn't mean the current mass in question is not a tumor, as my primary cancer presentation as well as my first metastasis both occurred without any spike in CEA levels. The next step is to check metabolic activity with a PET scan. If the mass is a steatosis, it won't light up the PET. If it's scar tissue from the last surgery, it will light up the PET but not as much as a tumor would.
So, an ambiguous but encouraging result. Now waiting to find out when I get a PET scan, or if my oncologist has some other advice.