Response Genetics (RGDX) SC 13D RESPONSE GENETICS / SRB Management ownership change

Exhibit 3

Power of Attorney

January 26, 2010

Securities and Exchange Commission

450 Fifth Street, NW

Washington, DC 20549

This letter confirms that Richard J. Birns is authorized and designated to sign all securities related filings with the Securities and Exchange Commission, including Forms 3, 4 and 5, on my behalf and on behalf of each entity for which I may sign such filings.  This authorization and designation shall be valid until either revoked in writing by the undersigned or until three years from the date of this letter.

Very truly yours,

/s/ Matthew A. Drapkin                                                      

Matthew A. Drapkin