1. Nature of Business, Basis of Presentation and Segment Information

Nature of Business

Karyopharm Therapeutics Inc., a Delaware corporation (collectively with its subsidiaries, the “Company,” “we,” “us,” or “our”), is a commercial-stage pharmaceutical company pioneering novel cancer therapies and dedicated to the discovery, development and commercialization of first-in-class drugs directed against nuclear export for the treatment of cancer. Our scientific expertise is based upon an understanding of the regulation of intracellular communication between the nucleus and the cytoplasm. We have discovered and are developing and commercializing novel, small molecule XPO1 inhibitor compounds that inhibit the nuclear export protein exportin 1. Our primary focus is on marketing XPOVIO® (selinexor) in its currently approved indications in multiple myeloma, as well as developing and seeking regulatory approval of selinexor in myelofibrosis. We were incorporated in Delaware on December 22, 2008 and have a principal place of business in Newton, Massachusetts.

Our lead asset, XPOVIO, received its initial U.S. approval from the U.S. Food and Drug Administration in July 2019 and is currently approved and marketed in the U.S. for the following indications: (i) in combination with bortezomib and dexamethasone for the treatment of adult patients with multiple myeloma who have received at least one prior therapy and (ii) in combination with dexamethasone for the treatment of adult patients with relapsed or refractory multiple myeloma who have received at least four prior therapies and whose disease is refractory to at least two proteasome inhibitors, at least two immunomodulatory agents, and an anti-CD38 monoclonal antibody. The commercialization of XPOVIO and NEXPOVIO® (selinexor) (the brand name for selinexor in Europe and the United Kingdom) outside of the U.S. is managed by our partners in their respective territories. XPOVIO/NEXPOVIO has received regulatory approvals in various indications in more than 50 territories and countries outside the U.S. and is commercially available in a growing number of countries as our partners continue to secure reimbursement approvals.

Liquidity, Capital Resources and Going Concern

We have historically financed our operations primarily through a combination of proceeds from (i) product revenue sales; (ii) public and private placements of equity securities; (iii) the issuance of convertible debt; (iv) a term loan; (v) our deferred royalty obligation; (vi) at the market offerings; and (vii) business development activities. As of June 30, 2026, we had $65.1 million of cash, cash equivalents, and investments and an accumulated deficit of $1.8 billion. We have incurred significant operating losses since our inception and we anticipate that we will continue to incur significant operating losses to support our continued operations and maintain our research and development programs, including as we continue to develop and seek regulatory approval of selinexor for myelofibrosis. As a result, our continued operations are dependent on our ability to raise additional funding or enter into other strategic alternatives and marketing XPOVIO in its currently approved indications. Based on our current business plan and current capital resources, combined with the uncertainty regarding the availability of additional funding or other strategic alternatives and considering our debt service obligations and financial covenant to maintain minimum liquidity, we have concluded that there is substantial doubt regarding our ability to continue as a going concern within one year after the date the accompanying condensed consolidated financial statements are issued.

We expect that our existing liquidity, including cash, cash equivalents, and investments together with anticipated cash flow from net product revenue and license and other revenue, will enable us to fund our current operating plans into September 2026. With the assistance of our advisors, including our financial advisor Centerview Partners and other advisors, we are actively evaluating a range of financing opportunities and strategic alternatives with the objective of extending our cash runway, preserving strategic flexibility and maximizing long-term shareholder value as we advance our myelofibrosis program. On September 10, 2026, a $15.8 million principal payment is due under our senior secured term loan facility; if this payment is made without additional financing or a waiver from our lenders, we expect that (i) our cash, cash equivalents and investments will fall below our $10.0 million minimum liquidity covenant, which would trigger a default on our term loan and (ii) we will not have sufficient resources to fund our operations following such payment. In addition to the $15.8 million principal payment due on September 10, 2026, we have approximately $10.1 million of aggregate interest payments due on September 30, 2026 under our senior secured term loan, 2028 Notes and 2029 Notes, all as defined below.

Our ability to successfully consummate a financing transaction or execute on a strategic alternative is dependent on a number of factors. There is no assurance that these efforts will result in additional funding, executing a strategic alternative transaction, will increase value for stakeholders, or will sufficiently address our ability to continue as a going concern. Absent additional funding or our ability to successfully complete one or more strategic transactions to extend our cash runway beyond September 10, 2026, we will be unable to continue as a going concern. There can be no assurance that we will be able to obtain additional funding or complete a strategic transaction, and we may have to consider seeking protection under the bankruptcy laws, liquidating our assets or ceasing our

operations. If we decide to seek protection under the bankruptcy laws, we expect that we would file for bankruptcy protection at a time that is earlier than when we would otherwise exhaust our cash resources. In any of these circumstances, it is likely that investors will lose all or part of their investment. If there remains substantial doubt about our ability to continue as a going concern, investors or other financing sources may be unwilling to provide funding to us on commercially reasonable terms, if at all. The accompanying condensed consolidated financial statements do not include any adjustments to the carrying amounts and classification of assets and liabilities that may be necessary if we were unable to continue as a going concern.

The significant accounting policies used in preparation of these condensed consolidated financial statements in this Form 10-Q are consistent with those discussed in Note 2, “Summary of Significant Accounting Policies,” in our Annual Report.