A polymeric scaffold useful for conjugating with a protein based recognition-molecule (PBRM) to form a PBRM-polymer-drug conjugate is described herein. The scaffold includes one or more terminal maleimido groups. Also disclosed is a PBRM-polymer-drug conjugate prepared from the scaffold. Compositions comprising the conjugates, methods of their preparation, and methods of treating various disorders, such as cancer in a subject having low HER2 expression with the conjugates or their compositions are also described.