A member of the heregulin superfamily has been identified which is designated".gamma.-HRG". This molecule, secreted by human breast cancer MDA-MB-175cells, leads to the formation of a constitutive active receptor complex andstimulates the growth of these cells in an autocrine manner. .gamma.-HRGpolypeptide and nucleic acid are disclosed, together with various usestherefor (e.g. use of .gamma.-HRG nucleic acid for the recombinant productionof .gamma.-HRG). .gamma.-HRG antagonists (e.g. neutralizing antibodies andantisense nucleic acid molecules) as well as uses therefor are also described.
