I Was Diagnosed In 2016 With Diffuse Large B-cell Lymphoma

I was diagnosed in 2016 with diffuse large B-cell lymphoma based on a FNA; however, removal of the swollen lymph node in my neck proved that I did not have it. Since then I've been followed for possible low-grade lymphoma after another node swelled up. Have had PET/CTs every 6 months and blood work: LDH, complete metabolic panel, CBC - which have been good. Had my latest scan last week and will be my oncologist this Wed.; but I noticed on my labs, he's not doing the LDH but a CEA instead. From what I've read, the CEA test is for other cancers, not lymphoma. Why would he be checking this? Thank you!