A nucleic acid molecule or construct alone or with a promoter suitable for expression control is contemplated that codes for a KLH1 haemocyanin, a haemocyanin domain or a fragment thereof with the immunological properties of at least one domain of haemocyanin, and comprises at least one intron sequence, as well as haemocyanin fusion proteins. The construct can also comprise a nucleic acid sequence that codes for an antigen. Host cells are also contemplated that contain the nucleic acid molecule or construct and a recombinant expression product thereof. The invention further relates to a pharmaceutical composition that comprises the expression product and antibodies obtainable by immunization of an animal therewith, as well as the use of antibodies in screening methods for the identification of tumors.