Syndax Pharmaceuticals Reports Second Quarter 2020 Financial Results and Provides Clinical and Business Update - Emerging data for SNDX-5613 support several protocol enhancements to AUGMENT- 101 to expand enrollment to p

Syndax Pharmaceuticals Reports Second Quarter 2020 Financial Results and

Provides Clinical and Business Update

- Emerging data for SNDX-5613 support several protocol enhancements to AUGMENT-

101 to expand enrollment to pediatric patients and focus exclusively on patients with

MLL-r and NPM1 mutant acute leukemias -

- Recommended Phase 2 dose and initiation of Phase 2 portion of AUGMENT-101

anticipated by year end; full Phase 1 data presentation expected in early 2021 -

- Results from Phase 1 trial of axatilimab in patients with cGVHD expected in 4Q20 -

- Company to host conference call today at 4:30 p.m. ET -

WALTHAM, Mass., August 6, 2020 -- Syndax Pharmaceuticals, Inc. ("Syndax," the "Company" or "we") (Nasdaq:SNDX), a clinical stage biopharmaceutical company developing an innovative pipeline of cancer therapies, today reported its financial results for the second quarter ended June 30, 2020. In addition, the Company provided a clinical and business update.

"We are very pleased that the FDA has agreed to several proposed changes to the Phase 1 portion of AUGMENT-101 which build on emerging clinical data and help us maximize SNDX-5613's potential in as many appropriate patients as possible," said Briggs W. Morrison, M.D., Chief Executive Officer of Syndax. "This includes focusing enrollment exclusively on patients with MLL-r and NPM1 mutant acute leukemias, the ability to expand dose cohorts that demonstrate efficacy, and inclusion of pediatric patients as young as one month, which has long been a key component of our overall strategy for SNDX-5613. We remain on track to identify a recommended Phase 2 dose by the end of this year, with full Phase 1 data now anticipated in early 2021."

Dr. Morrison added, "Progress also continues with the Phase 1/2 trial of axatilimab, our anti-CSF-1R monoclonal antibody, in patients with cGVHD, with Phase 1 results expected in the fourth quarter. We are actively committed to helping people with cancer live longer and better than ever before and look forward to further advancing this mission throughout the balance of the year."

Financial Update and Guidance

As of June 30, 2020, Syndax had cash, cash equivalents and short-term investments of $186.8 million and 44.1 million shares and share equivalents issued and outstanding which included 38.5 million shares of common stock and pre-funded warrants to purchase 5.6 million shares of common stock.

In May 2020, Syndax closed an underwritten public offering whereby the Company sold 6.4 million shares of common stock at a price of $18.00 per share. The aggregate net proceeds received by the Company were $107.9 million, net of underwriting discounts and commissions and estimated offering expenses payable by the Company.

Second quarter 2020 research and development expenses decreased to $10.9 million from $12.3 million for the prior year period. The second quarter decrease was primarily due to the impact of a $4.0 million expense for achievement of a clinical milestone associated with SNDX-5613 which was recognized and recorded in the second quarter of 2019. Excluding this milestone, research and development expenses in the second quarter of 2020 increased compared to the prior year period primarily due to an increase in clinical activities related to SNDX-5613 and axatilimab, and professional fees, partially offset by a decrease in clinical activities related to entinostat.

General and administrative expenses for the second quarter 2020 increased to $6.0 million from $3.5 million for the prior year period. The increase was primarily due to increased pre-commercialization activities in advance of the phase 3 breast cancer results for entinostat and employee related expenses.

For the three months ended June 30, 2020, Syndax reported a net loss attributable to common stockholders of $17.1 million or $0.42 per share compared to $14.9 million or $0.47 per share for the prior year period.

Today the Company provided operating expense guidance for the third quarter and second half of 2020. For the third quarter and second half of 2020, research and development expenses are expected to be $14 to $16 million and $30 to $35 million, respectively, and total operating expenses are expected to be $19 to $21 million and $40 to $45 million, respectively.

Conference Call and Webcast

In connection with the earnings release, Syndax's management team will host a conference call and live audio webcast at 4:30 p.m. ET today, Thursday, August 6, 2020.

The live audio webcast and accompanying slides may be accessed through the Events & Presentations page in the Investors section of the Company's website at www.syndax.com. Alternatively, the conference call may be accessed through the following:

Conference ID: 8998873

Domestic Dial-in Number: (855) 251-6663

International Dial-in Number: (281) 542-4259

Live webcast: https://edge.media-server.com/mmc/p/sdfqemqh

For those unable to participate in the conference call or webcast, a replay will be available on the Investors section of the Company's website, www.syndax.com.

About Syndax Pharmaceuticals, Inc.

Syndax Pharmaceuticals is a clinical stage biopharmaceutical company developing an innovative pipeline of cancer therapies. The Company's pipeline includes SNDX-5613, a highly selective inhibitor of the Menin-MLL binding interaction, axatilimab, a monoclonal antibody that blocks the colony stimulating factor 1 (CSF-1) receptor, and entinostat, a class I HDAC inhibitor. For more information, please visit www.syndax.com or follow the Company on Twitter and LinkedIn.

Syndax's Cautionary Note on Forward-Looking Statements

This press release contains forward-looking statements within the meaning of the Private Securities Litigation Reform Act of 1995. Words such as "may," "will," "expect," "plan," "anticipate," "estimate," "intend," "believe" and similar expressions (as well as other words or expressions referencing future events, conditions or circumstances) are intended to identify forward-looking statements. These forward-looking statements are based on Syndax's expectations and assumptions as of the date of this press release. Each of these forward-looking statements involves risks and uncertainties. Actual results may differ materially from these forward-looking statements. Forward-looking statements contained in this press release include, but are not limited to, statements about the progress, timing, clinical development and scope of clinical trials and the reporting of clinical data for Syndax's product candidates, the potential use of our product candidates to treat various cancer indications, Syndax's expected third quarter research and development expenses, and expected total operating expenses. Many factors may cause differences between current expectations and actual results including unexpected safety or efficacy data observed during preclinical or clinical trials, clinical trial site activation or enrollment rates that are lower than expected, changes in expected or existing competition, changes in the regulatory environment, the COVID-19 pandemic may disrupt our business and that of the third parties on which we depend, including delaying or otherwise disrupting our clinical trials and preclinical studies, manufacturing and supply chain, or impairing employee productivity, failure of Syndax's collaborators to support or advance collaborations or product candidates and unexpected litigation or other disputes. Other factors that may cause Syndax's actual results to differ from those expressed or implied in the forward-looking statements in this press release are discussed in Syndax's filings with the U.S. Securities and Exchange Commission, including the "Risk Factors" sections contained therein. Except as required by law, Syndax assumes no obligation to update any forward-looking statements contained herein to reflect any change in expectations, even as new information becomes available.