Constellation Pharmaceuticals : Corporate Presentation—May 10, 2021

Developing Next-Generation Epigenetic Treatments for Cancer Patients

Corporate Presentation

Stellar Science, Breakthrough Medicine

May 10, 2021

Forward-Looking Statements

This presentation contains forward-looking statements within the meaning of The Private Securities Litigation Reform Act of

1995 that involve substantial risks and uncertainties, including statements regarding the implications and potential of, and expectations regarding, preliminary or interim clinical data, the Company's plans, strategies and prospects for its business, beliefs and expectations about the Company's development and regulatory prospects and timelines, and statements regarding the development status and potential benefit of the Company's product candidates. The words "anticipate," "believe," "continue," "could," "estimate," "expect," "intend," "may," "plan," "potential," "predict," "project," "should," "target," "will," "would" and similar expressions are intended to identify forward-looking statements, although not all forward-looking statements contain these identifying words. Any forward-looking statements are based on management's current expectations of future events and are subject to a number of risks and uncertainties that could cause actual results to differ materially and adversely from those set forth in, or implied by, such forward-looking statements. These risks and uncertainties include, but are not limited to, risks associated with the Company's ability to: obtain and maintain necessary approvals from the FDA and other regulatory authorities; continue to advance its product candidates in clinical trials; whether preliminary or interim data from a clinical trial will be predictive of the final results of the trial; replicate in later clinical trials positive results found in preclinical studies and early-stage clinical trials of pelabresib (CPI-0610),CPI-0209 and CPI-482; advance the development of its product candidates under the timelines it anticipates, or at all, in current and future clinical trials; obtain, maintain, or protect intellectual property rights related to its product candidates; manage expenses; raise the substantial additional capital needed to achieve its business objectives; and the impact of the COVID-19 pandemic on the Company's business and operations, including on its ongoing clinical trials and regulatory activities, and on the general economic and market conditions. CPI-0610,CPI-0209 and CPI-482 are investigational therapies and have not been approved by the FDA (or any other regulatory authority). For a discussion of other risks and uncertainties, any of which could cause the Company's actual results to differ from those contained in the forward-looking statements, see the "Risk Factors" section, as well as discussions of potential risks, uncertainties, and other important factors, in the Company's most recent filings with the Securities and Exchange Commission, including the Company's Annual Report on Form 10-Q for the quarter ended March 31, 2021. In addition, the forward-looking statements included in this presentation represent the Company's views as of the date hereof and should not be relied upon as representing the Company's views as of any

date subsequent to the date hereof. The Company anticipates that subsequent events and developments will cause the Company's views to change. However, while the Company may elect to update these forward-looking statements at some point in the future, the Company specifically disclaims any obligation to do so.

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Constellation Vision

Create a Leading Hematology and Oncology Research,

Development, and Commercial Organization

Build a Fully Integrated Pharmaceutical Company

Execute Pivotal Development / Launch Pelabresib (CPI-0610) and

Transform Myelofibrosis Standard of Care

Establish POC in New Indications for Pelabresib and Demonstrate Best-in- Class Potential for CPI-0209 (EZH2i)

Strategically Invest in Discovery for Long-Term Success

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Broad Pipeline of Novel Hematology and Oncology Therapeutics

Product Candidates	Indications	Preclinical	Phase 1	Phase 2	Phase 3

BET

Pelabresib (CPI-0610)	Myelofibrosis
Second Generation EZH2 Inhibitor
CPI-0209	Solid Tumors/
Heme Malignancies
LSD1
CPI-482	Heme Malignancies
Discovery
Multiple Tumor Targeted and Tumor	Solid Tumors
Microenvironment (Undisclosed)

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Pelabresib (CPI-0610) Highlights

First Novel Mechanism Beyond JAK Inhibitors to Demonstrate POC in 1L MF

• Robust response rate to date in trial of > 60 1L patients
• Strong activity observed as a monotherapy and add on to ruxolitinib 2L+ patients
• Translational data and improvement in anemia supports disease-modifying potential
• Pelabresib has been generally well-tolerated to date
• Phase 3 trial (MANIFEST-2) under way

Preliminary MANIFEST data based on cut off date of September 29, 2020 SVR35 = ≥35% spleen volume reduction from baseline

(Pelabresib + Ruxolitinib in JAK-Naïve Patients)

Spleen Volume Change at Week 24

SVR35: 67% (42/63)

[95% CI: 54, 78]

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