CEA rise

My mother had cancer twice, once colonrectal (stage 3) in 2002 and once breast in 2008. Both got surgically removed followed by chemo (and radio for breast). She just got a call from her oncologist for a borderline CEA level (around 5.5). As far as we can remember, the pre-surgical CEA levels were both lower than 5 (could be ~2.5, I don't know the exact value). She also noticed that her CEA has slowly crept up in the last 3 tests (1.5, 2.5, 2.8).
Could this rise be an indication of recurrence or metastasis? Or could it be of a different origin? She's going to the doctor this Wed but I just want to get some extra advice on the issue before hand. She is extremely worried.