Additional Study Information: This is the first study in humans for an investigational drug called CX-2009. CX-2009 is a Probody therapeutic containing a masked antibody (an antibody is a protein naturally occurring in the human body to fight infections and in some cases tumors) attached to a maytansine derivative (a cancer killing therapy). The study is being done to look at the possible side effects, safety and tolerability of CX-2009. If you qualify for the study, you will be placed in one of 3 study parts (Part A, A2, and B). Each study part will consist of a screening period, treatment period, and follow-up period. Cancer types: breast cancer, castration-resistant prostate cancer, non-small cell lung cancer, epithelial ovarian cancer, endometrial cancer, head and neck squamous cell cancer, or cholangiocarcinoma (bile duct cancer).