Targeting Disease at the Nuclear Pore Karyopharm Reports First Quarter 2017 Financial Results and Highlights Recent Progress Pivotal Phase 3 BOSTON Study Expected to Commence in May 2017 Secured $52.2 Million Through Rec

Karyopharm Reports First Quarter 2017 Financial Results and Highlights Recent Progress

Pivotal Phase 3 BOSTON Study Expected to Commence in May 2017

Secured $52.2 Million Through Recent Equity Financing and ATM Facility

Conference Call Scheduled for Today at 8:30 a.m. ET

NEWTON, Mass. May 4, 2017 Karyopharm Therapeutics Inc. (Nasdaq:KPTI), a clinical-stage pharmaceutical company, today reported

financial results for the first quarter 2017 and commented on recent accomplishments and clinical development plans for its lead, novel, oral Selective Inhibitor of Nuclear Export (SINE ) compound selinexor

(KPT-330), and other pipeline assets verdinexor (KPT-335), and KPT-9274, its oral, dual inhibitor of p21-activated kinase 4 (PAK4) and nicotinamide phosphoribosyltransferase (NAMPT).

It s been a highly active

early 2017 for Karyopharm, marked most notably by establishment of a planned approval path for selinexor in relapsed or refractory diffuse large B-cell lymphoma (DLBCL), our second lead indication after

multiple myeloma (MM), following the presentation of robust interim data from the Phase 2b SADAL study at the American Association for Cancer Research (AACR) 2017 Annual Meeting, said Michael G. Kauffman, MD, PhD, Chief Executive Officer of

Karyopharm. After the observation of a 28.6% overall response rate (ORR) with over 7 months median duration of response (DOR), we consulted with the U.S. Food and Drug Administration (FDA) and obtained their agreement to amend the SADAL study

to focus solely on the 60mg twice weekly treatment cohort, in which we plan to enroll up to 90 more patients. Assuming we continue to see the response rate and durability observed to date, we plan to use the data from the SADAL study to support a

request for accelerated approval in DLBCL. Looking ahead, we remain focused on the initiation of the pivotal Phase 3 BOSTON study where we will evaluate selinexor in combination with Velcade

(bortezomib) and dexamethasone in patients with myeloma previously treated with one to three regimens, moving selinexor into much earlier lines of treatment.

Dr. Kauffman continued, Importantly, during April 2017, we strengthened our balance sheet by raising net proceeds of approximately

$52.2 million in equity financings, including approximately $37.8 million in an underwritten public offering and $14.5 million through our at-the-market

(ATM) offering program. We plan to use these funds to support the continued clinical development of selinexor in our lead indications, including in multiple myeloma, DLBCL and other oncology indications, with a focus on filing for accelerated

approvals for both myeloma and DLBCL during 2018. In addition, we expect this capital will fund our operations into 2019, while we are preparing to establish a commercial infrastructure for the potential launch of selinexor in North America and

First Quarter 2017 and Recent Events, Highlights and Milestones:

Selinexor in Multiple Myeloma (MM)

Selinexor in Diffuse Large

B-Cell Lymphoma (DLBCL)

As a result of these findings, and in consultation with the FDA, Karyopharm is amending the SADAL study

protocol to become a single-arm study focusing solely on single-agent selinexor dosed at 60mg twice weekly, eliminating the 100mg arm. The study is also being amended to reduce the 14-week treatment-free period to 8 weeks in patients who achieved at least a partial response (PR) on their most recent therapy. Patients whose disease was refractory or did not achieve at least a PR on their prior

therapy will continue with the 14-week treatment-free period. The FDA agreed that the modification to a single-arm study was reasonable and that the proposed trial

design and indication appear appropriate for accelerated approval, though eligibility for accelerated approval will depend on the complete trial results and available therapies at the time of regulatory action. The Company plans to enroll up to an

additional 90 patients to the 60mg single-arm cohort and expects to report top-line results from the SADAL study in mid-2018.

Selinexor in Other Hematologic Malignancies

Selinexor in Solid Tumors

Other Corporate and Clinical Developments

First Quarter 2017 Financial Results

Cash, cash equivalents and investments as of March 31, 2017, including restricted cash, totaled $150.6 million, compared to $175.5 million as of

On April 28, 2017, Karyopharm completed an underwritten public offering of 3,902,439 shares of its common stock at a price

to the public of $10.25 per share. The net proceeds to Karyopharm from the offering, after deducting the underwriting discounts and commissions and estimated offering expenses, were approximately $37.8 million. In addition, during April 2017,

the Company completed the sale of approximately 1.3 million shares under the ATM offering facility for net proceeds of approximately $14.5 million.

For the quarter ended March 31, 2017, research and development expense was $24.1 million compared to $21.8 million for the quarter ended

March 31, 2016. For the quarter ended March 31, 2017, general and administrative expense was $6.3 million compared to $5.6 million for the quarter ended March 31, 2016.

Karyopharm reported a net loss of $29.9 million, or $0.71 per share, for the quarter ended March 31, 2017, compared to a net loss of

$27.1 million, or $0.75 per share, for the quarter ended March 31, 2016. Net loss includes stock-based compensation expense of $5.9 million and $5.2 million for the quarters ended March 31, 2017 and March 31, 2016,

its operating cash burn, including research and development and general and administrative expenses, for the year ending December 31, 2017 to be in the range of $85 to 90 million. Based on current operating plans, Karyopharm expects that

its existing cash and cash equivalents, along with the $52.2 million of net proceeds raised in April 2017, will be sufficient to fund its research and development programs and operations into 2019, including the continued clinical development

of selinexor in our lead indications with a focus on filing for accelerated approvals for both MM and DLBCL during 2018, and preparing a commercial infrastructure for the potential launch of selinexor in North America and Western Europe.

Conference Call Information:

Karyopharm will host a

conference call today, Thursday, May 4, 2017, at 8:30 a.m. Eastern Time, to discuss the first quarter 2017 financial results, recent accomplishments, clinical developments and business plans. To access the conference call, please

dial (855) 437-4406 (US) or (484) 756-4292 (international) at least five minutes prior to the start time and refer to conference ID: 10603764. An

audio recording of the call will be available under Events & Presentations in the Investor section of Karyopharm s website, http://www.karyopharm.com, approximately two hours after the event.

About Karyopharm Therapeutics

Karyopharm Therapeutics

Inc. (Nasdaq:KPTI) is a clinical-stage pharmaceutical company focused on the discovery and development of novel first-in-class drugs directed against nuclear transport

and related targets for the treatment of cancer and other major diseases. Karyopharm s SINE compounds function by binding with and inhibiting the nuclear export protein XPO1 (or CRM1). The Company s initial focus is on seeking

regulatory approval and commercialization of its lead drug candidate, oral selinexor (KPT-330). To date, over 2,000 patients have been treated with selinexor and it is currently being evaluated in several mid- and later-phase clinical trials across multiple cancer indications, including multiple myeloma in combination with low-dose dexamethasone (STORM) and backbone therapies

(STOMP), diffuse large B-cell lymphoma (SADAL), and liposarcoma (SEAL),

among others. Karyopharm plans to initiate a pivotal randomized Phase 3 study of selinexor in combination with bortezomib (Velcade ) and low-dose dexamethasone (BOSTON) in patients with multiple myeloma in May 2017. In addition to single-agent and combination activity against a variety of human cancers, SINE compounds have also shown biological

activity in models of neurodegeneration, inflammation, autoimmune disease, certain viruses and wound-healing. Karyopharm, which was founded by Dr. Sharon Shacham, currently has five investigational programs in clinical or preclinical

development. For more information, please visit www.karyopharm.com.

Forward-Looking Statements

This press release contains forward-looking statements within the meaning of The Private Securities Litigation Reform Act of 1995. Such forward-looking

statements include those regarding the therapeutic potential of and potential clinical development plans for Karyopharm s drug candidates, including the timing of initiation of certain trials and of the reporting of data from such trials, and

Karyopharm s financial outlook. Such statements are subject to numerous important factors, risks and uncertainties that may cause actual events or results to differ materially from Karyopharm s current expectations. For example, there can

be no guarantee that any of Karyopharm s SINE compounds, including selinexor (KPT-330), KPT-8602, Karyopharm s next generation SINE compound, or KPT-9274, Karyopharm s first-in-class oral dual inhibitor of PAK4 and NAMPT, or any other drug candidate that Karyopharm is

developing, will successfully complete necessary preclinical and clinical development phases or that development of any of Karyopharm s drug candidates will continue. Further, there can be no guarantee that any positive developments in

Karyopharm s drug candidate portfolio will result in stock price appreciation. Management s expectations and, therefore, any forward-looking statements in this press release could also be affected by risks and uncertainties relating to a

number of other factors, including the following: Karyopharm s results of clinical trials and preclinical studies, including subsequent analysis of existing data and new data received from ongoing and future studies; the content and timing of

decisions made by the FDA and other regulatory authorities, investigational review boards at clinical trial sites and publication review bodies, including with respect to the need for additional clinical studies; Karyopharm s ability to obtain

and maintain requisite regulatory approvals and to enroll patients in its clinical trials; unplanned cash requirements and expenditures; development of drug candidates by Karyopharm s competitors for diseases in which Karyopharm is currently

developing its drug candidates; and Karyopharm s ability to obtain, maintain and enforce patent and other intellectual property protection for any drug candidates it is developing. These and other risks are described under the caption

Risk Factors in Karyopharm s Annual Report on Form 10-K for the year ended December 31 2016, which was filed with the Securities and Exchange Commission (SEC) on March 16, 2017, and

in other filings that Karyopharm may make with the SEC in the future. Any forward-looking statements contained in this press release speak only as of the date hereof, and, except as required by law, Karyopharm expressly disclaims any obligation to

update any forward-looking statements, whether as a result of new information, future events or otherwise.

Velcade is a registered trademark of Takeda Pharmaceutical Company Limited

Darzalex is a registered trademark of Janssen Biotech, Inc.

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Karyopharm Therapeutics Inc.

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