Diagnostic test for early stage cancer

1. A method of detecting a cancer cell-derived exosome from a subject comprising:

(a) providing a sample from said subject;

(b) contacting said sample with phosphatidylserine (PS) binding agent or agents, wherein said binding agent comprises a β2GP1 PS-binding domain; and

(c) detecting binding of said binding agent to PS expressed on the outer leaflet of the particle membrane of said exosome, thereby detecting said exosome.

2. The method of claim 1 , wherein said sample is a fluid.

3. The method of claim 2 , wherein said fluid is blood, serum, plasma, sputum, urine, saliva or tears.

4. The method of claim 1 , wherein said PS binding agent or agents exhibits increased binding to PS in the absence of calcium, as compared to binding to PS in the presence of calcium.

5. The method of claim 1 , wherein the sample is essentially free of available calcium or unchelated calcium.

6. The method of claim 1 , wherein said PS binding agent or agents is/are bound directly or indirectly to a support.

7. The method of claim 6 , wherein said PS binding agent or agents is bound to said support indirectly through an antibody.

8. The method of claim 7 , wherein said antibody is monomeric, dimeric or tetrameric.

9. The method of claim 1 , wherein detecting comprises contacting the sample of step (b) with an exosome binding agent.

10. The method of claim 1 , wherein detecting is quantitative.

11. The method of claim 1 , wherein said cancer cell-derived exosome is from a lung cancer cell, a pancreatic cancer cell, an ovarian cancer cell, a colon cancer cell, a renal cancer cell, a liver cancer cell, a skin cancer cell, a brain cancer cell, a head and neck cancer cell, or a thyroid cancer cell.

12. The method of claim 1 , further comprising enriching, concentrating or purifying exosomes prior to step (b).

13. The method of claim 1 , wherein the subject is a human or a non-human mammal.

14. The method of claim 1 , further comprising administering a cancer therapy to said subject.