Compositions and methods for delivering an agent to a cell comprising a prolactin receptor are provided. Also provided is a method of inhibiting a breast, ovarian or prostate cancer cell, where the method includes a step of contacting the cell with a complex comprising a prolactin receptor ligand linked to at least one of an RNAi-inducing agent, a polynucleotide sequence encoding a polypeptide, an miRNA, a cytotoxic moiety, a chemotherapeutic moiety, a radioactive moiety or a nanoparticle. Methods of detecting a cancer cell expressing a prolactin receptor are also provided.