carcinoembryonic antigen peptide-1 carcinoembryonic antigen peptide-1 carcinoembryonic antigen peptide-1 is a nine amino acid peptide fragment of carcinoembryonic antigen (cea), a protein that is overexpressed in several cancer cell types, including gastrointestinal, breast, and non-small-cell lung. synonyms: cap-1 carcinoembryonic antigen peptide-1 carcinoembryonic peptide-1 cea peptide 1 cea peptide 9-mer