I am not an expert at all, but let me share my understanding. Hopefully those with more experience will chip in soon enough.
CEA is not a good marker for everybody, having said this, CEA is more sensitive to liver mets than it is to lung mets, you did not mention how much your husband´s CEA increased and whether this was a good marker in the past.
One thing that stries me as uncommon is the fact that your husband has been NED for quite a long time, liver mets are typically early occurences, while local recurrences are more common after the 3 year mark. Has your husband had a colonoscopy to discard a local recurrence in colon? SORRY, I realize he had one this year as described in signature.
So the liver lesion might still be a benign and the CEA rise a random occurence, but if it turns out to be a metastasis, then there are several possible routes:
Surgery offers the best outcome, it may be followed up with systemic chemo and additional hepatic chemo. You may want to request a Signatera test for residual disease, to assess the need of post surgical chemo and its effectiveness.
For surgery to be an option a number of requirements need to be met, there is some room for flexibility but in general the requirments are as follow:
-the number of lesions is small.
-the liver that can be left after resection is enough to survive.
-there is no evidence of extra-hepatic disease.
Second best is to first apply chemotherapy to reduce the size and number of lesions (to meet the requirements above) and then go for surgery
A HAI pump is a way to deliver chemo to the liver only, this is often accompanied with systemic chemo
If chemo manages to shrink the lesion then surgery becomes an option.
Here is an excellent video on HAI: https://www.mskcc.org/videos/treating-liver-metastases-hepatic-arterial-infusion-therapy?fbclid=IwAR1J4J8Fehr7FxzSnIR9zIGzXuSeaUCxI2F_8-uTLWWj7f9to5JzKQxGyFU
As I said, I am not an expert, hopefully people with more knowledge will soon contribute.