The invention provides methods for diagnosing prostate cancer. The invention also provides novel anti-STEAP-1 antibodies and uses thereof.

Disclosed is a method of determining ceruloplasmin activity using a mass spectrometry technique. The method comprises reacting a biological sample containing ceruloplasmin with a compound of formula I to produce an oxidized product of the compound, measuring a level of the oxidized product by a mass spectrometry technique, and determining a level of ceruloplasmin activity based on the level (amount) of the oxidized product.

Provided herein are antibodies which bind to ceruloplasmin and are useful for various applications, including detecting ceruloplasmin and immunocapturing ceruloplasmin in biological samples. The antibodies are useful in methods of measuring non-ceruloplasmin-bound copper concentrations and labile-bound copper concentrations in biological samples.