EXHIBIT 10.4

[Geron Letterhead]

September 24, 2013

Stephen N. Rosenfield
[Home Address]

     RE:   First Amendment to Employment Agreement

Dear Stephen:

By this First Amendment to your Employment Agreement (the “First Amendment”),
you and the Company agree to amend your Employment Agreement, dated February 16,
2012 (the “Agreement”), by deleting Section 3.2 of the Agreement in its entirety
and replacing it with the following:

     “3.2 Bonus. Executive shall be eligible to earn, for each fiscal year of
the Company ending during Executive’s employment with the Company, an annual
discretionary cash bonus (an “Annual Bonus”) targeted at forty-five percent
(45%) of Executive’s Base Salary. If the Company determines, in it reasonable
discretion, that Executive has engaged in any misconduct intended to affect the
payment of his/her Annual Bonus, or has otherwise engaged in any act or omission
that would constitute Cause for termination of employment, as defined by Section
1.2 of the Agreement, Executive will automatically and immediately forfeit
his/her entire Annual Bonus. If the Annual Bonus has already been paid to
Executive, such Annual Bonus will be deemed unearned, and the Company shall have
the right to recover the entire amount of the Annual Bonus paid to Executive for
the calendar year(s) in which such misconduct or other act or omission
constituting Cause occurred. Without limiting the foregoing, any such misconduct
or other act or omission constituting Cause will subject Executive to
disciplinary action up to and including termination of employment. In addition,
any Annual Bonus paid to Executive for the calendar year(s) in which such
misconduct or other Cause occurred is subject to recoupment in accordance with
The Dodd–Frank Wall Street Reform and Consumer Protection Act and any
implementing regulations, any other clawback policy adopted by the Company and
any compensation recovery policy otherwise required by applicable laws,
regulations or statutes. Recovery by the Company of an Annual Bonus in
accordance with this Section shall not constitute an event giving rise to a
right by Executive to voluntarily terminate his/her employment for cause based
on such recovery by Company, nor shall it constitute “constructive termination”,
or any similar term or circumstance under the Agreement or any other plan or
agreement with the Company.”

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In consideration for your execution of this First Amendment, your employment by
the Company will continue on the terms and conditions set forth in the
Agreement, as amended hereby. In addition, Section 4.1(ii)(d) of the Agreement
shall be amended by deleting the word “subsequent” and replacing it with the
phrase “other (i.e. granted prior or subsequently to the date hereof)”, such
that the amended Section shall read:

     “(d) the Option, along with any other options (i.e. granted prior or
subsequently to the date hereof) or other exercisable equity interest in the
Company held by Executive, shall remain outstanding and exercisable through the
earlier of (i) the second (2nd) anniversary of the date of termination or (ii)
the original expiration date of the option or other equity interest.”

Please sign below to indicate your agreement hereto.

Sincerely,

GERON CORPORATION   By:  /s/ John A. Scarlett September 24, 2013        John A.
Scarlett, M.D. Date      Chief Executive Officer

ACKNOWLEDGED AND AGREED TO:     Stephen N. Rosenfield     Print Name     /s/
Stephen N. Rosenfield September 24, 2013 Signature  

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