Syndax Pharmaceuticals Reports Third Quarter 2020 Financial Results and Provides Clinical and Business Update - Presentation of Phase 1 data from AUGMENT-101 trial of SNDX-5613 and initiation of Phase 2 on track for earl

Syndax Pharmaceuticals Reports Third Quarter 2020 Financial Results and

Provides Clinical and Business Update

- Presentation of Phase 1 data from AUGMENT-101 trial of SNDX-5613 and initiation of Phase

2 on track for early 2021 -

- Company provides update on axatilimab development plan in cGVHD following recent FDA

interactions; expects to commence pivotal trial by year-end -

- Data from Phase 1 trial of axatilimab in patients with cGVHD to be highlighted during oral

presentation at ASH Annual Meeting in December -

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

WALTHAM, Mass., November 2, 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 third quarter ended September 30, 2020. In addition, the Company provided a clinical and business update.

"We continue to make exciting progress in the Phase 1 portion of the AUGMENT-101 trial of SNDX-5613, our highly selective, potent, oral menin inhibitor, in adult and pediatric patients with acute leukemias that harbor MLL-r and NPM1 genetic alterations," said Briggs W. Morrison, M.D., Chief Executive Officer of Syndax. "We are highly encouraged by initial data from this study, which demonstrated clear clinical activity in this difficult to treat population of patients with genetically defined acute leukemias. We remain on track to present Phase 1 data from AUGMENT-101 and commence the Phase 2 portion in early 2021."

Dr. Morrison added, "In addition, following recent interactions with the FDA, we are excited to take the next step of initiating a pivotal trial for axatilimab, our anti-CSF-1R monoclonal antibody, in patients with cGVHD which we expect by the end of this year. We are encouraged by the clinical activity and overall safety we've seen in the ongoing trial, and firmly believe axatilimab has the potential to serve as an effective intervention for patients with cGVHD. We look forward to sharing updated results from the Phase 1 trial during an oral presentation at the ASH Annual Meeting in December."

Financial Update and Guidance

As of September 30, 2020, Syndax had cash, cash equivalents and short-term investments of $170.2 million and 44.4 million shares and share equivalents issued and outstanding which included 38.8 million shares of common stock and pre-funded warrants to purchase 5.6 million shares of common stock.

Third quarter 2020 research and development expenses increased to $14.4 million from $9.9 million for the prior year period. The increase was primarily due to increased clinical activity for SNDX-5613 and axatilimab and a $2.0 million milestone payable to UCB upon the achievement of a certain milestone.

General and administrative expenses for the third quarter 2020 increased to $5.8 million from $3.6 million for the prior year period. This increase was primarily due to employee related expenses including a one-time non-cash stock compensation expense.

For the three months ended September 30, 2020, Syndax reported a net loss attributable to common stockholders of $20.4 million or $0.46 per share compared to $12.8 million or $0.41 per share for the prior year period.

For the fourth quarter of 2020, research and development expenses are expected to be $15 to $20 million, and total operating expenses are expected to be $20 to $25 million.

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, Monday, November 2, 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: 7974533

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

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

Live webcast: https://edge.media-server.com/mmc/p/62ujymuo

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 fourth 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.