The present invention relates to antibodies and related molecules that immunospecifically bind to TRAIL receptor, TR4. Such antibodies have uses, for example, in the treatment of cancers and other proliferative disorders. The invention also relates to nucleic acid molecules encoding anti-TR4 antibodies, vectors and host cells containing these nucleic acids, and methods for producing the same. The present invention relates to methods and compositions for detecting, diagnosing, treating or ameliorating a disease or disorder, especially cancer and other hyperproliferative disorders, comprising administering to an animal, preferably a human, an effective amount of one or more antibodies or fragments or variants thereof, or related molecules, that immunospecifically bind to TRAIL receptor TR4.