EXHIBIT 4.1

LOGO



EXHIBIT 4.1



|                                                          |  |                                                      |  |                                         
|--------------------------------------------------------- |  | ---------------------------------------------------- |  | ----------------------------------------
|NUMBER                                                    |  | COUGAR BIOTECHNOLOGY                                 |  | SHARES                                  
|                                                          |  |                                                     
|THIS CERTIFICATE IS TRANSFERABLE IN SOUTH SAINT PAUL, MN. |  | INCORPORATED UNDER THE LAWS OF THE STATE OF DELAWARE |  | SEE REVERSE SIDE FOR CERTAIN DEFINITIONS



| |  |  |  |                  
| |  |  |  | -----------------
| |  |  |  | CUSIP 222083 10 7

THIS CERTIFIES THAT

is the owner of

FULLY PAID AND NON-ASSESSABLE COMMON SHARES, $.0001 PAR VALUE, OF

COUGAR
BIOTECHNOLOGY, INC.

transferable on the books of the Corporation by the holder hereof in person or by Attorney upon
surrender of this certificate properly endorsed. This certificate is not valid unless countersigned by the Transfer Agent and Registrar.

IN WITNESS WHEREOF, the said Corporation has caused this certificate to be signed by facsimile signatures of its duly authorized officers.

Dated:

|                           |  |                                         
|-------------------------- |  | ----------------------------------------
|/S/    ILLEGIBLE SECRETARY |  | /S/    ILLEGIBLE CHIEF EXECUTIVE OFFICER



|                                                    
|----------------------------------------------------
|COUNTERSIGNED AND REGISTERED: WELLS FARGO BANK, N.A.
|TRANSFER AGENT AND REGISTRAR                        
|BY            /S/    TODD MAY                       
|AUTHORIZED SIGNATURE                                





---

LOGO



THE BOARD OF THIS
CORPORATION HAS THE AUTHORITY TO CREATE AND DETERMINE THE RELATIVE RIGHTS AND PREFERENCES OF CLASSES OR SERIES OF SHARES OF CAPITAL STOCK OTHER THAN COMMON STOCK. THIS CORPORATION WILL FURNISH TO ANY SHAREHOLDER UPON WRITTEN REQUEST SENT TO ITS
PRINCIPAL EXECUTIVE OFFICES, AND WITHOUT CHARGE, A FULL STATEMENT OF THE BOARDS AUTHORITY TO CREATE AND DETERMINE THE RELATIVE RIGHTS AND PREFERENCES OF CLASSES OR SERIES OF SHARES OF CAPITAL STOCK AS WELL AS THE DESIGNATIONS, PREFERENCES,
LIMITATIONS AND RELATIVE RIGHTS OF THE SHARES OF EACH CLASS OR SERIES THEN OUTSTANDING OR AUTHORIZED TO BE ISSUED.

The
following abbreviations, when used in the inscription on the face of this certificate, shall be construed as though they were written out in full according to applicable laws or regulations:



|                                                                                  |  |                                                                               
|--------------------------------------------------------------------------------- |  | ------------------------------------------------------------------------------
|TEN COM - as tenants in common                                                    |  | UTMA -
                     Custodian (Cust)
                          (Minor)
|TEN ENT - as tenants by entireties                                                |  | under Uniform Transfer to Minors                                              
|                                                                                  | 
|JT TEN - as joint tenants with right of survivorship and not as tenants in common |  | Act (State)                                                                   
|Additional abbreviations may also be used though not in the above list.          

For value received
             hereby sell, assign and transfer unto

|                                                                     
|---------------------------------------------------------------------
|                                                                     
|PLEASE INSERT SOCIAL SECURITY OR OTHER IDENTIFYING NUMBER OF ASSIGNEE
|                                                                     

PLEASE PRINT OR TYPEWRITE NAME AND ADDRESS INCLUDING POSTAL ZIP CODE
OF ASSIGNEE





Shares of the capital stock represented by the within Certificate, and do hereby irrevocably constitute and appoint

_____________________________________________________________ Attorney

to
transfer the said stock on the books of the within-named Corporation with full power of substitution in the premises.

Dated
                                         X

X

NOTICE: THE SIGNATURE TO THIS ASSIGNMENT MUST CORRESPOND WITH THE NAME AS WRITTEN UPON THE FACE

OF
THE CERTIFICATE IN EVERY PARTICULAR WITHOUT ALTERATION OR ENLARGEMENT OR ANY CHANGE WHATEVER.

|                                                                                                                                                                                                                                                                                                                                                                       
|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
|                                                                                                                                                                                                                                                                                                                                                                       
|SIGNATURE GUARANTEED                                                                                                                                                                                                                                                                                                                                                   
|ALL GUARANTEES MUST BE MADE BY A FINANCIAL INSTITUTION (SUCH AS A BANK OR BROKER) WHICH IS A PARTICIPANT IN
THE SECURITIESTRANSFER AGENTS MEDALLION PROGRAM (STAMP), THE NEW YORK STOCK EXCHANGE, INC. MEDALLION SIGNATURE PROGRAM (MSP), OR THESTOCK EXCHANGES MEDALLION PROGRAM (SEMP) AND MUST NOT BE DATED.
GUARANTEES BY A NOTARY PUBLIC ARE NOT ACCEPTABLE.