Methods and compositions are provided for assessing, treating, and preventing diseases, especially cancer, using cancer-associated targets (“CAT”). Methods and compositions are also provided for determining or predicting the effectiveness of a treatment for these diseases or for selecting a treatment, using CAT. Methods and compositions are further provided for modulating cell function using CAT. Also provided are compositions that modulate CAT (e.g., antagonists or agonists), such as antibodies, proteins, small molecule compounds, and nucleic acid agents (e.g., RNAi and antisense agents), as well as pharmaceutical compositions thereof. Further provided are methods of screening for agents that modulate CAT, and agents identified by these screening methods.