seser b i o 1Q 2021 Business Update May 10, 2021 NASDAQ: SESN FORWARD- LOOKING STATEMENTS This presentation contains forward-looking statements that involve substantial risks and uncertainties. All statements, other than statements of historical facts, contained in this presentation, including statements regarding our strategy, future operations, clinical development of our protein therapies, future financial position, future revenues, projected costs, prospects, plans and objectives of management, are forw ...

Table of Contents 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 March 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: 001-36296 Sesen Bio, Inc. (Exact name of registrant as specified in its charter) Delaware 26-2025616 (State or ot ...

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 Title of each class Trading Symbol(s) Name of each exchange on which registered Common Stock, $0.001 par value SESN The Nasdaq Global Market 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, 2020 OR ☐ TRANSITION REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 For the transition period from _____ to _____ Commiss ...

Table of Contents 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 September 30, 2020 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: 001-36296 Sesen Bio, Inc. (Exact name of registrant as specified in its charter) Delaware 26-2025616 (State o ...

Financial Data and Key Metrics Changes - The company reported a cash balance of $42 million at the end of Q3 2020, an increase from $38 million at the end of Q2 2020, indicating effective capital management [34][37] - Cash used in operations for the quarter was $14 million, primarily for activities related to the BLA submission and regulatory support [35] Business Line Data and Key Metrics Changes - The company is on track to complete the BLA submission by the end of 2020, with potential FDA approval projected for mid-2021 [13][14] - The market opportunity for Vicinium is estimated to be substantial, with potential peak sales ranging from $1 billion to $3 billion [15][31] Market Data and Key Metrics Changes - The company conducted market research indicating that over 80% of high prescribers of bladder cancer would choose Vicinium over Keytruda, highlighting a favorable perception of Vicinium in the market [17][18] - The company is focusing on key markets including the U.S., Europe, China, and MENA, with ongoing negotiations for partnerships in these regions [33] Company Strategy and Development Direction - The company aims to establish a 50-50 value share partnership for marketing authorization in Europe, indicating a strategic approach to market entry [41] - The company emphasizes a robust supply chain with partnerships with world-class manufacturers to ensure reliable production of Vicinium [20] Management's Comments on Operating Environment and Future Outlook - Management expressed confidence in the regulatory path forward in both the U.S. and Europe, with a clear understanding of the requirements for approval [5][9] - The company highlighted the significant unmet need in bladder cancer and the differentiated clinical profile of Vicinium as key drivers for future growth [5][38] Other Important Information - The company received $10 million in net proceeds from Qilu Pharmaceutical, which is crucial for funding operations without dilution [34] - The ATM facility has generated approximately $16 million year-to-date, providing an efficient source of capital for ongoing projects [36] Q&A Session Summary Question: What are the final steps needed with Module 3 before the BLA submission? - Management confirmed that all testing is completed, and the final step involves finalizing the statistical analysis and documentation for Module 3 [40][42] Question: What are the long-term plans in Europe regarding partnerships? - Management indicated plans to seek a partner for the European market, aiming for a 50-50 value share arrangement [41]

seser i b O 3Q 2020 Business Update November 9, 2020 FORWARD-LOOKING STATEMENTS This presentation contains forward-looking statements that involve substantial risks and uncertainties. All statements, other than statements of historical facts, contained in this presentation, including statements regarding our strategy, future operations, clinical development of our protein therapies, future financial position, future revenues, projected costs, prospects, plans and objectives of management, are forwardlooking ...

Table of Contents Title of each class Trading Symbol(s) Name of each exchange on which registered Common Stock, $0.001 par value SESN The Nasdaq Stock Market 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, 2020 OR ☐ TRANSITION REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 For the transition period from t ...

seser b i o 2020 Jefferies Healthcare Conference Thomas Cannell DVM, President & CEO For Investor Purposes Only June 2, 2020 NASDAQ: SESN FORWARD-LOOKING STATEMENTS This presentation contains forward-looking statements that involve substantial risks and uncertainties. All statements, other than statements of historical facts, contained in this presentation, including statements regarding our strategy, future operations, clinical development of our protein therapies, future financial position, future revenue ...

Table of Contents Title of each class Trading Symbol(s) Name of each exchange on which registered Common Stock, $0.001 par value SESN The Nasdaq Stock Market 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 March 31, 2020 OR ☐ TRANSITION REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 For the transition period from ...

Financial Data and Key Metrics Changes - The company finished Q1 2020 with approximately $42.5 million in cash and cash equivalents, which is deemed sufficient to fund strategic priorities into 2021 [50] - The company carries no debts, which is considered a strength in the current environment [52] Business Line Data and Key Metrics Changes - The company successfully completed the manufacturing of the pre-PPQ batch at Fuji, demonstrating meaningful progress for CMC comparability [14] - The pre-PPQ batch met all quality acceptance criteria, indicating a positive review on the ability to demonstrate analytical comparability during the Process Performance Qualification (PPQ) campaign [30][34] Market Data and Key Metrics Changes - The market research indicates that approximately 30% of urologists treat about 75% of non-muscle invasive bladder cancer patients, allowing for a focused sales force of roughly 40 to 50 representatives [43] - The company estimates that the peak sales in Europe will be higher than in the United States due to a larger patient population and higher incidence rates of bladder cancer [64] Company Strategy and Development Direction - The company aims to leverage digital and social media to reach caregivers and family members who influence treatment decisions, which is seen as an efficient and scalable commercial approach [46][47] - The company is planning to initiate a confirmatory trial around the time of U.S. approval, with a design to compare against standard care chemotherapeutic agents [77] Management's Comments on Operating Environment and Future Outlook - Management expressed confidence in the strong commercial opportunities supported by recent market research results, highlighting the differentiated mechanism of action of Vicinium [13] - The company remains on track to complete the BLA submission in the second half of 2020, with potential U.S. approval anticipated in the first half of 2021 [37] Other Important Information - The company has instituted a flexible work-from-home policy for all employees in Canada and the U.S., ensuring that internal operations continue at normal levels [10] - The company has received positive feedback from the European Medicines Agency (EMA) regarding the marketing authorization application for Vicinium, with no additional clinical trials requested [39] Q&A Session Summary Question: Can you walk us through the next steps regarding manufacturing? - The company has completed the pre-PPQ run at Fuji and the first PPQ run at Baxter, with plans to conduct three consecutive runs this summer at Fuji [57] Question: What additional analyses does the EMA require? - The EMA prefers controlled clinical trials with survival endpoints, contrasting with the FDA's focus on single-arm trials [60] Question: What is the market opportunity for non-muscle invasive bladder cancer in Europe? - The incidence of bladder cancer in Europe is estimated to be two to three times that of the U.S., indicating a significant market opportunity [64] Question: What are the expectations regarding prior authorizations and step edits from payers? - Payers are expected to have minimal step edits and prior authorizations, focusing on high-grade non-muscle invasive bladder cancer patients [70] Question: How does the company view the confirmatory trial's impact on market access? - A successful confirmatory trial is expected to improve global access and reimbursement opportunities in both the U.S. and Europe [80] Question: Are there significant differences in bladder cancer treatment between the U.S. and Europe? - Generally, treatment practices are similar, with both regions using BCG as the first-line standard of care [83]