Filing

UNITED STATES
SECURITIES AND EXCHANGE COMMISSION
WASHINGTON, DC 20549

SCHEDULE 13G

Under the Securities Exchange Act of 1934
(Amendment No.1)*


Mast Therapeutics, Inc.
(Name of Issuer)


Common Stock
(Title of Class of Securities)


576314108
(CUSIP Number)


January 9, 2017
(Date of Event Which Requires Filing of this Statement)


       Check the appropriate box to designate the rule pursuant to which this
Schedule is filed:
[_]  Rule 13d-1(b)

[X]  Rule 13d-1(c)

[_]  Rule 13d-1(d)

__________
       *The remainder of this cover page shall be filled out for a reporting
person's initial filing on this form with respect to the subject class of
securities, and for any subsequent amendment containing information which
would alter the disclosures provided in a prior cover page.
       The information required in the remainder of this cover page shall not
be deemed to be filed for the purpose of Section 18 of the Securities
Exchange Act of 1934 (Act) or otherwise subject to the liabilities of that
section of the Act but shall be subject to all other provisions of the Act
(however, see the Notes).
?
CUSIP No.
576314108





1.
NAME OF REPORTING PERSONS








Sabby Healthcare Master Fund, Ltd.




2.
CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP (SEE INSTRUCTIONS)


(a)  [_]


(b)  [X]



3.
SEC USE ONLY










4.
CITIZENSHIP OR PLACE OF ORGANIZATION





Cayman Islands




NUMBER OF SHARES BENEFICIALLY OWNED BY EACH REPORTING PERSON WITH



5.
SOLE VOTING POWER





0




6.
SHARED VOTING POWER





22,779,672




7.
SOLE DISPOSITIVE POWER





0




8.
SHARED DISPOSITIVE POWER





22,779,672




9.
AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON




22,779,672




10.
CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN
SHARES (SEE INSTRUCTIONS)



[_]






11.
PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (9)





9.56




12.
TYPE OF REPORTING PERSON (SEE INSTRUCTIONS)

              CO?
CUSIP No.
576314108





1.
NAME OF REPORTING PERSONS








Sabby Volatility Warrant Master Fund, Ltd.




2.
CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP (SEE INSTRUCTIONS)


(a)  [_]


(b)  [X]



3.
SEC USE ONLY










4.
CITIZENSHIP OR PLACE OF ORGANIZATION





Cayman Islands




NUMBER OF SHARES BENEFICIALLY OWNED BY EACH REPORTING PERSON WITH



5.
SOLE VOTING POWER





0




6.
SHARED VOTING POWER





1,496,700




7.
SOLE DISPOSITIVE POWER





0




8.
SHARED DISPOSITIVE POWER





1,496,700




9.
AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON




1,496,700




10.
CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN
SHARES (SEE INSTRUCTIONS)



[_]






11.
PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (9)





0.63




12.
TYPE OF REPORTING PERSON (SEE INSTRUCTIONS)

              CO?

CUSIP No.
576314108





1.
NAME OF REPORTING PERSONS








Sabby Management, LLC




2.
CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP (SEE INSTRUCTIONS)


(a)  [_]


(b)  [X]



3.
SEC USE ONLY










4.
CITIZENSHIP OR PLACE OF ORGANIZATION





Delaware, USA




NUMBER OF SHARES BENEFICIALLY OWNED BY EACH REPORTING PERSON WITH



5.
SOLE VOTING POWER





0




6.
SHARED VOTING POWER





 23,799,222




7.
SOLE DISPOSITIVE POWER





0




8.
SHARED DISPOSITIVE POWER





 23,799,222




9.
AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON




 23,799,222




10.
CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN
SHARES (SEE INSTRUCTIONS)



[_]






11.
PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (9)





9.99




12.
TYPE OF REPORTING PERSON (SEE INSTRUCTIONS)

              OO
CUSIP No.
576314108





1.
NAME OF REPORTING PERSONS








Hal Mintz




2.
CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP (SEE INSTRUCTIONS)


(a)  [_]


(b)  [X]



3.
SEC USE ONLY










4.
CITIZENSHIP OR PLACE OF ORGANIZATION





USA




NUMBER OF SHARES BENEFICIALLY OWNED BY EACH REPORTING PERSON WITH



5.
SOLE VOTING POWER





0




6.
SHARED VOTING POWER





 23,799,222




7.
SOLE DISPOSITIVE POWER





0




8.
SHARED DISPOSITIVE POWER





 23,799,222




9.
AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON




 23,799,222




10.
CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN
SHARES (SEE INSTRUCTIONS)



[_]






11.
PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (9)





9.99




12.
TYPE OF REPORTING PERSON (SEE INSTRUCTIONS)

              IN?

CUSIP No.
576314108



Item 1.
(a).
Name of Issuer:







Mast Therapeutics, Inc.



(b).
Address of issuer's principal executive offices:







3611 Valley Centre Drive, Suite 500
San Diego, California 92130


Item 2.
(a).
Name of person filing:







Sabby Healthcare Master Fund, Ltd.
Sabby Volatility Warrant Master Fund, Ltd.
Sabby Management, LLC
Hal Mintz




(b).
Address or principal business office or, if none, residence:




Sabby Healthcare Master Fund, Ltd.
c/o Ogier Fiduciary Services (Cayman) Limited
89 Nexus Way, Camana Bay
Grand Cayman KY1-9007
Cayman Islands

Sabby Volatility Warrant Master Fund, Ltd.
c/o Ogier Fiduciary Services (Cayman) Limited
89 Nexus Way, Camana Bay
Grand Cayman KY1-9007
Cayman Islands

Sabby Management, LLC
10 Mountainview Road, Suite 205
Upper Saddle River, New Jersey 07458

Hal Mintz
c/o Sabby Management, LLC
10 Mountainview Road, Suite 205
Upper Saddle River, New Jersey 07458







(c).
Citizenship:




Sabby Healthcare Master Fund, Ltd. - Cayman Islands
Sabby Volatility Warrant Master Fund, Ltd. - Cayman Islands
Sabby Management, LLC - Delaware, USA
Hal Mintz - USA







(d).
Title of class of securities:







Common stock (the Common Stock)



(e).
CUSIP No.:







576314108


Item 3.
If This Statement is filed pursuant to Section 240.13d-1(b) or 240.13d-2(b),
or(c), check whether the person filing is a


(a)
[_]
Broker or dealer registered under section 15 of the Act (15 U.S.C. 78o).


(b)
[_]
Bank as defined in section 3(a)(6) of the Act (15 U.S.C. 78c).


(c)
[_]
Insurance company as defined in section 3(a)(19) of the Act (15 U.S.C. 78c).


(d)
[_]
Investment company registered under section 8 of the Investment Company Act
of 1940 (15 U.S.C. 80a-8).


(e)
[_]
An investment adviser in accordance with Section 240.13d-1(b)(1)(ii)(E);


(f)
[_]
An employee benefit plan or endowment fund in accordance with Section
240.13d-1(b)(1)(ii)(F);


(g)
[_]
A parent holding company or control person in accordance with Section
240.13d-1(b)(1)(ii)(G);



(h)
[_]
A savings association as defined in Section 3(b) of the Federal Deposit
Insurance Act (12 U.S.C.1813);


(i)
[_]
A church plan that is excluded from the definition of an investment company
under section 3(c)(14) of the Investment Company Act of 1940 (15 U.S.C.
80a-3);


(j)
[_]
A non-U.S. institution in accordance with Section 240.13d-1(b)(1)(ii)(J);


(k)
[_]
Group, in accordance with Section 240.13d-1(b)(1)(ii)(K).  If filing as a
non-U.S.institution in accordance with Section 240.13d-1(b)(1)(ii)(J),
please specify the type of institution:







Item 4.
Ownership.


Provide the following information regarding the aggregate number and
percentage of the class of securities of the issuer identified in Item 1.


(a)
Amount beneficially owned:

Sabby Healthcare Master Fund, Ltd. - 22,779,672

Sabby Volatility Warrant Master Fund, Ltd. - 1,496,700

Sabby Management, LLC -  23,799,222

Hal Mintz -  23,799,222


(b)
Percent of class:

Sabby Healthcare Master Fund, Ltd. - 9.56%

Sabby Volatility Warrant Master Fund, Ltd. - 0.63%

Sabby Management, LLC - 9.99%

Hal Mintz - 9.99%






(  (c)
Number of shares as to which the person has:



Sabby Healthcare Master Fund, Ltd.



( (i)
Sole power to vote or to direct the vote
0
,







( (ii)
Shared power to vote or to direct the vote
22,779,672
,







( (iii)
Sole power to dispose or to direct the disposition of
0
,







( (iv)
Shared power to dispose or to direct the disposition of
22,779,672
..








Sabby Volatility Warrant Master Fund, Ltd.



( (i)
Sole power to vote or to direct the vote
0
,







( (ii)
Shared power to vote or to direct the vote
1,496,700
,







( (iii)
Sole power to dispose or to direct the disposition of
0
,







( (iv)
Shared power to dispose or to direct the disposition of
1,496,700
..




Sabby Management, LLC



  (i)
Sole power to vote or to direct the vote
0
,







( (ii)
Shared power to vote or to direct the vote
 23,799,222
,







( (iii)
Sole power to dispose or to direct the disposition of
0
,







( (iv)
Shared power to dispose or to direct the disposition of
 23,799,222
..








Hal Mintz



( (i)
Sole power to vote or to direct the vote
0
,







( (ii)
Shared power to vote or to direct the vote
 23,799,222
,







( (iii)
Sole power to dispose or to direct the disposition of
0
,







( (iv)
Shared power to dispose or to direct the disposition of
 23,799,222
..








As calculated in accordance with Rule 13d-3 of the Securities Exchange Act of
1934, as amended, (i) Sabby Healthcare Master Fund, Ltd. and Sabby
Volatility Master Fund, Ltd. beneficially own 22,779,672 and 1,496,700 shares of
the Issuer's common stock ("Common Stock"), respectively, representing
approximately 9.56% and 0.63% of the Common Stock, respectively, and
(ii) Sabby Management, LLC and Hal Mintz each beneficially own 23,799,222
 shares of the Common Stock, representing approximately 9.99% of the Common
Stock. Sabby Management, LLC and Hal Mintz do not directly own any shares of
Common Stock, but each indirectly owns 23,799,222 shares of
Common Stock. Sabby Management, LLC, a Delaware limited liability company,
indirectly owns  23,799,222 shares of Common Stock because it serves as the
investment manager of Sabby Healthcare Master Fund, Ltd. and Sabby
Volatility Warrant Master Fund, Ltd., Cayman Islands companies. Mr. Mintz
indirectly owns 23,799,222 shares of Common Stock in his capacity as
manager of Sabby Management, LLC.


Item 5.
Ownership of Five Percent or Less of a Class.


If this statement is being filed to report the fact that as of the date
hereof the reporting person has ceased to be the beneficial owner of more
than five percent of the class of securities, check the following  [ ].






?
Item 6.
Ownership of More Than Five Percent on Behalf of Another Person.





Not applicable



Item 7.
Identification and Classification of the Subsidiary Which Acquired the
Security Being Reported on by the Parent Holding Company or Control Person.





Not applicable



Item 8.
Identification and Classification of Members of the Group.





Not applicable



Item 9.
Notice of Dissolution of Group.





Not applicable



?
Item 10.
Certification.




By signing below I certify that, to the best of my knowledge and belief, the
securities referred to above were not acquired and are not held for the
purpose of or with the effect of changing or influencing the control of the
issuer of the securities and were not acquired and are not held in connection
with or as a participant in any transaction having that purpose or effect.



?
SIGNATURE

       After reasonable inquiry and to the best of my knowledge and belief,
I certify that the information set forth in this statement is true, complete
and correct.

 January 9, 2017

(Date)





Sabby Healthcare Master Fund, Ltd.

By: /s/ Harry Thompson
	Name:  Harry Thompson
 Title:   Authorized Person of TDF Management Ltd.,
a Director


Sabby Volatility Warrant Master Fund, Ltd.

By: /s/ Harry Thompson
	Name:  Harry Thompson
 Title:   Authorized Person of TDF Management Ltd.,
a Director


Sabby Management, LLC*

By: /s/ Robert Grundstein
	Name:  Robert Grundstein
       Title:   Chief Operating Officer







/s/ Hal Mintz*
 Hal Mintz

*This Reporting Person disclaims beneficial ownership over the securities
reported herein except to the extent of its pecuniary interest therein.

The original statement shall be signed by each person on whose behalf the
statement is filed or his authorized representative.  If the statement is
signed on behalf of a person by his authorized representative other than an
executive officer or general partner of the filing person, evidence of the
representative's authority to sign on behalf of such person shall be filed
with the statement, provided, however, that a power of attorney for this
purpose which is already on file with the Commission may be incorporated by
reference.  The name and any title of each person who signs the statement
shall be typed or printed beneath his signature.

Note.  Schedules filed in paper format shall include a signed original and
five copies of the schedule, including all exhibits. See s.240.13d-7 for other
parties for whom copies are to be sent.

Attention.  Intentional misstatements or omissions of fact constitute Federal
criminal violations (see 18 U.S.C. 1001).

EXHIBIT 1
----------

JOINT FILING AGREEMENT

       The undersigned hereby agree that this Statement on Schedule 13G with
respect to the beneficial ownership of shares of Common Stock of Cellectar
Biosciences Inc. is filed jointly, on behalf of each of them.

Dated:  January 9, 2017

Sabby Healthcare Master Fund, Ltd.

By: /s/ Harry Thompson
     Name:  Harry Thompson
     Title:   Authorized Person of TDF Management
Ltd.,    a Director

Sabby Volatility Warrant Master Fund, Ltd.

By: /s/ Harry Thompson
     Name:  Harry Thompson
     Title:   Authorized Person of TDF Management
Ltd.,    a Director



Sabby Management, LLC

By: /s/ Robert Grundstein
	Name:  Robert Grundstein
       Title:   Chief Operating Officer




/s/ Hal Mintz
 Hal Mintz