Abstract: The molecular cloning, expression, and biological characteristics of a novel receptor tyrosine kinase related to the epidermal growth factor receptor, termed HER4/p180.sup.erbB4, are described. Antibodies to HER4 are disclosed. A HER4 ligand capable of inducing cellular differentiation of breast cancer cells is also disclosed. In view of the expression of HER4 in several human cancers and in certain tissues of neuronal and muscular origin, various diagnostic and therapeutic uses of HER4-derived and HER4-related biological compositions are provided.

Abstract: Provided are drug/ligand compounds of Formula (I): ##STR1## (I) in whichD is a drug moiety;n is an integer from 1 to 10;p is an integer from 1 to 6;Y is O or NH.sub.2.sup.+ C1.sup.- ;z is 0 or 1;q is about 1 to about 10;X is a ligand; and,A is a Michael Addition Adduct.In a preferred embodiment, the ligand is an immunoglobulin, preferably a chimeric antibody or fragment thereof. Also provided are formulations comprising as an active ingredient a compound of Formula (I), intermediates useful for preparing the compounds of Formula (I), processes for preparing the compounds of Formula (I), and methods for using the compounds of the invention.