COMPOSITIONS AND METHODS FOR PROSTATE CANCER ANALYSIS

1 . A method for diagnosing prostate cancer in a test subject using CTCs, comprising:

a) identifying CTCs from a blood sample taken from the test subject;

b) contacting the CTCs with an antibody that specifically binds to STEAP1, an antibody that specifically binds to CD45, and an antibody that specifically binds to cytokeratin;

c) staining the CTCs with DAPI; and

d) detecting the DAPI stain and bound antibody with a tyramide signal amplification (TSA) protocol to enhance signal;

wherein the presence of CTCs that express cytokeratin and a prostate-specific marker and exhibit DAPI staining without CD45 expression is predictive of having prostate cancer in the test subject.

2 . The method of claim 1 , wherein anti-STEAP1 antibody is the 15A5 antibody, produced by a hybridoma cell having a microorganism deposit number of PTA-12259.

3 . The method of claim 1 , further comprising determining the expression level of STEAP1 on the cancer cells.

4 . The method of claim 1 , further comprising grading the cancer cells based on their expression level of STEAP1, and determining the percentage of the cancer cells in each grade.

5 . The method of claim 1 , further comprising calculating a grade score for each grade by multiplying the percentage of the cancer cells in said grade with a unique grade number representative of the expression level of the prostate-specific marker in said grade, and summing up all the grade scores to obtain an H score, wherein the H score is indicative of the stage of the prostate cancer in the test subject.

6 . The method of claim 1 , wherein the cancer cells are identified from the blood sample with a capturing composition comprising a ligand that specifically binds to cancer cells of epithelial origin.

7 . The method of claim 6 , wherein the ligand is an antibody that specifically binds to an epithelial antigen preferentially expressed on cancer cells.

8 . The method of claim 7 , wherein the epithelial antigen is Epithelial Cell Adhesion Molecule (EpCAM).

9 . The method of claim 6 , wherein the identified cancer cells are enriched in a cell fraction separated from the blood sample.

10 . The method of claim 9 , wherein the cell fraction is separated under a magnetic field.

11 . The method of claim 10 , wherein the ligand in the capturing composition is coupled to a magnetic particle.

12 . The method of claim 6 , wherein the ligand comprises an EpCAM antibody.

13 . The method of claim 1 , wherein the anti-STEAP-1 antibody binds to STEAP-1 with a K D of ≤1000 nM.

14 . The method of claim 1 , wherein the anti-STEAP-1 antibody, the anti-CD45 antibody, and/or the anti-cytokeratin antibody are conjugated with detectable labels.

15 . A method of predicting efficacy of STEAP1-ADC therapy in a test subject suffering from prostate cancer, comprising:

a) identifying CTCs from a blood sample taken from the test subject;

b) contacting the CTCs with an antibody that specifically binds to STEAP1, an antibody that specifically binds to CD45, and an antibody that specifically binds to cytokeratin;

c) staining the CTCs with DAPI; and

d) detecting the DAPI stain and bound antibody with a tyramide signal amplification (TSA) protocol to enhance signal;

wherein the presence of CTCs that express cytokeratin and STEAP1 and exhibit DAPI staining without CD45 expression is predictive of efficacy of the STEAP1-ADC.

16 . A method of monitoring response to STEAP1-ADC therapy in a test subject suffering from prostate cancer using a tyramide signal amplification (TSA) protocol to enhance signal, comprising:

a) contacting a first group of CTCs with an antibody that specifically binds to STEAP1, an antibody that specifically binds CD45, and an antibody that specifically binds cytokeratin, and staining the cells with DAPI, wherein the first group of cancer cells are from a first blood sample taken from the test subject before treatment with the STEAP1-ADC;

b) determining the number of CTCs in the first group that express STEAP1 and cytokeratin and stain with DAPI;

c) contacting a second group of CTCs with an antibody that specifically binds to STEAP1, an antibody that specifically binds CD45, and an antibody that specifically binds cytokeratin, and staining the cells with DAPI, wherein the second group of cancer cells are from a second blood sample taken from the test subject during or after treatment with the STEAP1-ADC;

d) determining the amount of the cancer cells in the second group that express STEAP1 and cytokeratin and stain with DAPI; and

e) comparing the amount of the CTCs that express STEAP1 and cytokeratin and stain with DAPI as determined in b) with that in d),

wherein a decrease in the amount of the CTCs and/or a decrease in the STEAP1+ CTCs indicates a response to the prostate cancer therapy in the test subject.

17 . The method of claim 15 or 16 , wherein the STEAP1-ADC comprises an anti-STEAP1 antibody covalently attached to a cytotoxic agent.

18 . The method of claim 17 , wherein the cytotoxic agent is selected from a toxin, a chemotherapeutic agent, a drug moiety, monomethylauristatin E (MMAE), an antibiotic, a radioactive isotope, and a nucleolytic enzyme.

19 . The method of claim 1 , wherein the DAPI, STEAP1, CD45, and cytokeratin signals are detected using FACS.

20 . The method of claim 1 , wherein the DAPI, STEAP1, CD45, and cytokeratin signals are detected using immunohistochemistry.