A biologically active complex comprising a polypeptide having the sequence of a naturally occurring protein or a variant thereof, wherein said polypeptide is at least partially unfolded as compared to the said naturally occurring protein for example as a result of a modification of at least one cysteine residue； or a peptide of up to 50 amino acids； and a fatty acid or lipid or a salt thereof, for use in prophylactic treatment of cancers, in particular of the gastrointestinal tract. Compositions that may comprise the complex and have use as nutraceuticals are obtainable from milk or milk fractions and form a further aspect of the invention. Methods of treatment in particular for the prevention of cancer form a further aspect of the invention.
