APUD tumor cells can uptake and decarboxylate amine precursor such as 5-hydroxy-L-tryptophan (5-HTP) and L-dihydroxyphenylalanine (L-DOPA) and pass through aromatic L-amino acid decarboxylase (AADC) to decarboxylate them to the corresponding 5-hydroxy-L-tryptamine and dopamine. Here, DDC is linked to neoplasm.