A nucleic acid molecule or construct alone or with a promoter suitable for expression control is contemplated that codes for a HLH2 haemocyanin polypeptide and comprises at least one intron sequence, as well as haemocyanin fusion proteins. The construct further can comprise a nucleic acid sequence that codes for an antigen. Host cells are also contemplated that contain the nucleic acid molecules or construct and recombinant expression product thereof. The invention further relates to a pharmaceutical composition that comprises the expression product of that nucleic acid and antibodies obtainable by immunization of an animal therewith, as well as use of the antibodies in screening methods for the identification of tumors.