0001374310-12-000013 DEFA14A 1 20120531 20120531 20120531 CBOE Holdings, Inc. 0001374310 6200 205446972 DE 1231 DEFA14A 34 001-34774 12880454 400 SOUTH LASALLE CHICAGO IL 60605 312 786 7200 400 SOUTH LASALLE CHICAGO IL 60605 DEFA14A 1 employeeletter.htm EMPLOYEE LETTER