UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 10-K (Mark One) ☒ ANNUAL REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 For the Fiscal Year Ended December 31, 2021 OR ☐ TRANSITION REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 For the Transition Period from to Commission File Number: 001-37708 Syndax Pharmaceuticals, Inc. Securities registered pursuant to Section 12(g) of the Act: None Indicate by check mark if the re ...

Determined to realize a future in which people with cancer live longer and better than ever before Syndax 參 CORPORATE PRESENTATION | JANUARY 2022 Forward-looking statements disclosure This presentation contains forward-looking statements within the meaning of the Private Securities Litigation Reform Act of 1995. Words such as "may," "will," "expect," "plan," "anticipate" and similar expressions (as well as other words or expressions referencing future events or circumstances) are intended to identify forwar ...

Pipeline Programs - Syndax's pipeline focuses on Menin Inhibitor Program (SNDX-5613) and Anti–CSF-1R Program (Axatilimab) targeting indications with significant unmet needs[5, 6, 7] - AUGMENT-101 trials are underway in NPM1 mut AML, MLLr ALL and MLLr AML, each enrolling 64 adults + up to 10 peds, using a dose of 163mg BID with any strong CYP3A4 inhibitor[9, 10] - ASH abstract data (June 2021 cut) for AUGMENT-101 showed a CRc (CR+CRh+CRp+CRi/MLFS) of 44% (20/45) and a CRc MRD- rate of 70% (14/20)[18] - Axatilimab's ASH abstract (June 2021 data cut) reported an Overall Response Rate of 66% (25/38) across all doses and 75% (18/24) at the 1 mg/kg q2wk dose[29] SNDX-5613 Expansion - Trials testing expanded opportunities for SNDX-5613 to initiate in 1H22, including BEAT-AML (Frontline Ven/Aza combo), AUGMENT-102 (R/R Chemo combo), and INTERCEPT (MRD-progression in AML)[20] - SNDX-5613 aims to expand market potential by moving into frontline treatment, targeting additional patients and increasing treatment duration[23] Axatilimab Collaboration - Syndax and Incyte have a global collaboration for axatilimab development, with Syndax funding 45% of global trials and Incyte funding 100% of regional trials[25] - The collaboration includes $117 million upfront, $35 million equity at a 30% premium, up to $450 million in additional milestones, and a 50:50 profit split[25] Financial Status - As of September 30, 2021, Syndax had $229.7 million in cash and short-term investments and 52.2 million shares outstanding[38] - The company's FY 2021 operating expense guidance includes $90-100 million for Research and Development and $110-120 million for Total Operating Expenses[39]

Syndax Pharmaceuticals, Inc. (NASDAQ:SNDX) Q3 2021 Earnings Conference Call November 15, 2021 4:30 PM ET Company Participants Melissa Forst - Argot Partners, Investor Relations Briggs Morrison - Chief Executive Officer Michael Metzger - President, Chief Operating Officer and Director Anjali Ganguli - Chief Business Officer Conference Call Participants Phil Nadeau - Cowen Justin Walsh - B. Riley Securities Joel Beatty - Baird Peter Lawson - Barclays Operator Good day and thank you for standing by. Welcome t ...

Washington, D.C. 20549 FORM 10-Q UNITED STATES SECURITIES AND EXCHANGE COMMISSION (Mark One) ☒ QUARTERLY REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 For the quarterly period ended September 30, 2021 or ☐ TRANSITION REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 For the transition period from to Commission File Number: 001-37708 Syndax Pharmaceuticals, Inc. (Exact Name of Registrant as Specified in Its Charter) Delaware 32-0162505 (State or Oth ...

Determined to realize a future in which people with cancer live longer and better than ever before Syndax §> 2Q21 EARNINGS PRESENTATION Forward-looking statements disclosure This presentation contains forward-looking statements within the meaning of the Private Securities Litigation Reform Act of 1995. Words such as "may," "will," "expect," "plan," "anticipate" and similar expressions (as well as other words or expressions referencing future events or circumstances) are intended to identify forward-looking ...

Financial Data and Key Metrics Changes - The net loss for Q2 2021 was $22.9 million, or $0.44 per share, compared to a net loss of $17.1 million, or $0.42 per share, for the same period last year [35] - The net loss was below the guidance of $35 million to $40 million due to the shifting of timing for some CMC activities [35] - The company ended Q2 2021 with $253.1 million in cash and cash equivalents, providing a cash runway into 2023 [36] Business Line Data and Key Metrics Changes - The Phase I trial of SNDX-5613 has shown a 48% overall response rate and a 23% CR/CRh rate in patients with relapsed or refractory acute leukemia [15][16] - Axatilimab is in a pivotal trial (AGAVE-201) for chronic graft versus host disease, with enrollment ongoing and top-line data expected in 2023 [28][29] Market Data and Key Metrics Changes - Approximately 14,000 patients in the U.S. suffer from chronic graft versus host disease, representing a significant commercial opportunity [29] - The company is exploring the use of SNDX-5613 in combination with venetoclax and azacitidine for newly diagnosed AML patients [22] Company Strategy and Development Direction - The company aims to be first to market in relapsed/refractory disease and to expand the 5613 franchise into additional indications [21] - There is a focus on obtaining regulatory approval for drugs that extend and improve the lives of patients with cancer and other diseases [40][41] - The company plans to continue expanding its pipeline through product acquisitions or in-licensing of differentiated assets [32] Management's Comments on Operating Environment and Future Outlook - Management expressed optimism about the ongoing registrational programs for both SNDX-5613 and axatilimab, viewing them as major achievements [40] - The management team is confident in their financial resources to advance programs and achieve key milestones [42] Other Important Information - The company has received Fast Track Designation from the FDA for SNDX-5613, with an end of Phase I meeting anticipated [17] - The Phase II portion of the AUGMENT-101 trial will enroll distinct cohorts, including pediatric and adult patients, potentially leading to a broad regulatory approval [20] Q&A Session Summary Question: Would you be willing to disclose the AUC or time above the IC90 for the recommended Phase II doses? - The company will look into this and get back with the information [46][47] Question: Will the updated data at year-end include those phased -- the initial experience from the recommended Phase II doses? - Yes, the updated data will include information from the intermediate doses [47] Question: What clarity do you hope to get from the FDA meeting? - The company seeks agreement on the recommended Phase II dose, endpoints, sample size, and potential registrational status for Phase II expansion cohorts [48] Question: Is it correct to think that there may be an exposure or PK extension benefit for 5613, given that venetoclax is a CYP3A4 inhibitor? - Venetoclax is metabolized by CYP3A4, and the company anticipates dose adjustments for both drugs when used in combination [51] Question: How are you thinking about the evolving landscape for axatilimab, especially with recent approvals? - The company believes axatilimab will provide a complementary mechanism for patients who have received other therapies [54] Question: Could you tell us more about the efforts to minimize QT prolongation? - The company has been working with clinical sites to ensure better electrolyte management, which has shown to reduce QT prolongation [56][57] Question: Could you elaborate on the trial design for the Beat AML trial? - The trial will start with a Phase I to determine the right dose, followed by a randomized trial [59] Question: How many patients do you think you could have as the Phase II pivotal starts? - The company has not specified the number but indicated that backfilling cohorts could count towards the Phase II enrollment [61] Question: What chemotherapies are you looking to combine with in AUGMENT-102? - The company plans to combine with FLAG-based regimens for AML and a 4-drug regimen typically used in ALL [63] Question: Are there other frontline trials you want to run? - The company is exploring various development opportunities, including combinations with standard care treatments [64]

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 10-Q (Mark One) ☒ QUARTERLY REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 For the quarterly period ended June 30, 2021 or ☐ TRANSITION REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 For the transition period from to Commission File Number: 001-37708 Syndax Pharmaceuticals, Inc. (Exact Name of Registrant as Specified in Its Charter) Delaware 32-0162505 (State or Other Ju ...

Financial Data and Key Metrics Changes - The net loss for Q1 2021 was $27.7 million, or $0.54 per share, compared to a net loss of $19.1 million, or $0.56 per share for the same period last year [37] - The company ended Q1 2021 with $271.3 million in cash and cash equivalents, providing a cash runway into 2023 [38] Business Line Data and Key Metrics Changes - The Phase 1 trial of SNDX-5613 reported a 48% overall response rate with 67% of responses being MRD negative in patients with relapsed or refractory acute leukemia [11][10] - Axatilimab's Phase 2 expansion cohort has been fully enrolled, with updated data expected later this year [27] Market Data and Key Metrics Changes - Approximately 14,000 patients in the U.S. suffer from chronic graft versus host disease, representing a significant commercial opportunity [31] Company Strategy and Development Direction - The company aims to initiate Phase 2 trials for SNDX-5613 by the end of Q2 2021 and is focused on obtaining regulatory approval for drugs that extend and improve the lives of cancer patients [22][43] - There is ongoing research into expanding the 5613 franchise beyond initial approvals in relapsed refractory acute leukemias [26] Management's Comments on Operating Environment and Future Outlook - Management expressed optimism about the broad franchise opportunities for both SNDX-5613 and axatilimab, indicating confidence in advancing their programs and achieving key milestones [44] - The management team highlighted the importance of identifying and bringing in novel molecules to deepen the company's portfolio [45] Other Important Information - The company expects R&D expenses for Q2 2021 to be between $30 million and $35 million, with total operating expenses between $35 million and $40 million [39] - Full-year 2021 guidance remains unchanged, with R&D expenses expected to be between $90 million and $100 million [40] Q&A Session Summary Question: Clarification on NPM1 patients and complete hematologic recovery - One of the two NPM1 patients had a complete response and full hematologic recovery, while no further information was provided on the second patient [48] Question: Goals for the new cohort in the dose escalation study - The cobicistat arm is exploratory and does not affect the doses moving into Phase 2 [49] Question: Concerns about the therapeutic window of SNDX-5613 - The recommended Phase 2 dose meets pre-specified criteria for efficacy, and the response rates are consistent with the overall population [51] Question: Specific goals of the interim dose cohort - The interim dose cohort is not a gating item for moving into Phase 2, but results will be evaluated before proceeding [54] Question: Protocol for stem cell transplants in the study - There is no formal protocol for stem cell transplants; it is based on the investigator's decision after achieving a complete response [59] Question: Effect of SNDX-5613 on ALL patients - Qualitatively, the effect appears similar in ALL as in AML, but the numbers are small [77] Question: Response rate for NPM1 patients compared to current standards - The response rate for relapsed refractory acute leukemia is generally low with chemotherapy, making the observed rates with SNDX-5613 significant [78]

Determined to realize a future in which people with cancer live longer and better than ever before Syndax §> 1Q21 EARNINGS PRESENTATION Forward-looking statements disclosure This presentation contains forward-looking statements within the meaning of the Private Securities Litigation Reform Act of 1995. Words such as "may," "will," "expect," "plan," "anticipate" and similar expressions (as well as other words or expressions referencing future events or circumstances) are intended to identify forward-looking ...