Is this after a chemo series?
107 is significant. (Some patients never have particularly elevated CEA even with mets, which is why they say it's not a good marker for them.) A drop to 3, which is in the normal range albeit a bit high for nonsmokers, is almost certainly significant. But without scans you can't really say how significant. It's almost certainly a positive sign, however.
What it can't really tell you is much about the future, since killing every single cancer cell with chemo happens but is fairly rare. But it's a decent start.
D/H Dx 10/2019 RC age 61
Clinical T4bN2M1a (common iliac and para-aortic lymph nodes)
MSS KRAS G12D
CRT 11/19-1/20 FOLFOX 3/20-7/20
Pelvic exenteration w/LAR 8/20
ypT4bN0Mx G3 0/14 nodes LVI not seen PNI-
CEA 10/19:20, 1/20-11/20:1.6, 4.3, 3.4, 2.7, 2/21:9.0 3/21:18,40 4/21:28,19, 5/21:13.3,8.6
PET 3/21 recurrence in distal nodes, L5 vertebra, pelvis