Mersana Therapeutics, Inc.

Good morning and welcome to Mursana Therapeutics Second Quarter 2025 Financial Results and Business Updates Conference Call and Webcast. Currently, all participants are in listen-only mode. There will be a question and answer session at the end of this call. Please note, this call is being recorded. I would now like to turn the call over to Jason Fredette, Senior Vice President, Investor Relations and Corporate Communications.

Thank you, operator, and good morning, everyone. Before we begin, please note that this call will contain forward-looking statements within the meaning of federal securities laws. These statements may include, but are not limited to, those related to the potential clinical benefits of our product candidates and platforms, our clinical trial progress and design, addressable market opportunities, and anticipated clinical milestones and data presentations, and cash runway. Each of these forward-looking statements is subject to risks and uncertainties that could cause actual results to differ materially from those projected in such statements. These risks and uncertainties are discussed in our quarterly report on Form 10-Q filed with the Securities and Exchange Commission on May 15, 2025, and in subsequent SEC filings. Our filings are available at sec.gov and on our website, mursana.com. Except as required by law, we assume no obligation to update forward-looking statements publicly, even if new information becomes available in the future. On today's call, we have Mursana's Chief Executive Officer, Dr. Marty Huber, and our Chief Operating Officer and Chief Financial Officer, Brian Descheitner. With that, let me turn the call over to Marty to begin the discussion.

Thank you, Jason, and good morning, everyone. The second quarter of 2025 was eventful for Mursana, particularly as it relates to Emily, our dolesynthin ADC targeting B7H4. Chief among the highlights were our oral presentations at ASCO 2025 and ESMO Breast Cancer 2025, and the strong enrollment progress we made in our expansion cohorts. At ASCO in Chicago, Dr. Erica Hamilton of the Sarah Cannon Research Institute presented data as of March 8th data cutoff across all patients who enrolled in our Emily Phase I dose escalation and backfill cohorts. safety and tolerability remained consistent with previously reported data. This presentation also included clinical activity data across all enrolled B7H4 expressing tumors. At intermediate doses ranging from about 38 milligrams per meter squared to 67 milligrams per meter squared, the confirmed objective response rate, or ORR, was 31% among the valuable patients with B7H4 high tumor expression, which we initially defined as a tumor proportion score of 70% or higher. The presentation also highlighted some intriguing activity that we have seen in adenoid cystic carcinoma type 1 or ACC1. This is a rare head and neck cancer with a very poor prognosis and no approved therapies. In the past, other development candidates, such as VEGF TKIs and NOTCH inhibitors, have investigated this tumor type and have shown response rates ranging from the mid-single digits to the mid-teens. Among the nine evaluable patients with ACC1 who received any dose of Emily regardless of B7H4 expression, we observed four confirmed responses and one unconfirmed objective response. And subsequent to the March 8th cutoff, that one UPR was confirmed for an objective response rate in ACC1 of 56%. In recent months, we have enrolled additional patients with ACC1 in backfill cohorts. While these data help to demonstrate EMILY's broader development potential, our focus today is on addressing the significant unmet needs of patients with triple negative breast cancer. or TNBC, who have previously been treated with a topoisomerase 1 inhibitor or topo 1 ADC, such as Tredelvi, Inher2, or Datraway. The standard of care today for these patients is single agent chemotherapy. And unfortunately, their expected outcomes are exceedingly poor. Based on reported data from the original ASCENT phase 3 trial of Tridelby in topo-naive patients with recurrent metastatic TNBC, the objective response rate, or ORR, for single-agent chemotherapy was 5%. Progression-free survival, or PFS, was 1.7 months, and overall survival, or OS, was 6.7 months. At the ESMO Breast Cancer Congress in Munich, Germany, Dr. Hamilton presented data as of that same March 8th cutoff from patients with TNBC who had received intermediate doses of Emily, highlighting patients who had received one to four prior lines of treatment. Nearly all of these patients also had received at least one previous TOPA-180C. Among the patients with B7H4 low TNBC who received an intermediate dose of Emily, observed clinical activity resembled today's standard of care with an ORR of zero, a median PFS of 6.4 weeks, and a median OS of 5.7 months. But among those patients who we have initially characterized as B7H4 high TMBC, who received an intermediate dose of EMILY, the ORR was 29%, the median PFS was 16 weeks, and the median OS had not yet been reached as of the data cutoff. It's data like these that led us to initiate dose expansion. And in recent months, we have continued to make progress in this phase of development. In expansion, we are enrolling patients with TNBC who have received one to four prior lines of treatment in the metastatic setting, including at least one prior topo-180C. We're investigating two Emily dosing regimens. Our dose A cohort is receiving a 67.4 milligram per meter squared dose of Emily every four weeks. And our dose B cohort is receiving 80 milligrams per meter squared dose of Emily every four weeks, following a loading dose of 44.5 milligrams per meter squared on days one and eight of the first four week cycle. Collectively, we have enrolled more than 45 patients across these two cohorts, and we remain on track to report initial clinical data from expansion in the second half of 2025. Now, finally, on the Emily front, we are often asked how big the post-Topo 1 TNBC opportunity is. We believe it is sizable and it has the potential to get substantially larger. As a reminder, today, Topo 1 ADCs with TNBC indications are only approved in the recurrent setting. Despite this, Tredelvi is already expected to generate about a billion dollars in global TNBC revenues in 2025. Of course, this figure does not include revenues that other Topo1 ADCs are generating in this setting, nor does it consider how the opportunity would increase as these agents move into early lines of therapy. For example, we believe the recent positive readouts of Ascent3 and Ascent4 will make Tredelvi the new frontline standard of care for patients with TNBC, which will greatly increase the post-Topo1 population of patients. As a reminder, emerging clinical data suggests that once a patient receives an initial topo-1 ADC, a subsequent topo-1 agent has substantially reduced benefit due to payload resistance. We believe this evolving treatment landscape opens the opportunity for a novel non-topo-1 agent like Emily to address the growing unmet need for topo-experienced patients if it is approved. So if a patient receives Tredelvi in the frontline, Emily could potentially be used as a second-line therapy. Or if a patient receives another topo-180C, such as in HER2, DATO-DXD, or SAC-TMT in the recurrent setting, Emily could potentially be used subsequent to that. Additionally, because of Emily's differentiated tolerability profile, we believe it could potentially be explored in combinations with other agents, including topo-180Cs, platinum chemotherapy, and PD-L1 agents. So let's move on to XMT2056, MRSANA's immunosynthin ADC targeting HER2. As a reminder, GSK has an exclusive global license option to co-develop and commercialize this candidate. XMT2056 is in the dose escalation portion of our phase one clinical trial, which is enrolling patients with a variety of HER2 expressing tumors. And we are pleased to report that in July, we achieved a $15 million development milestone under our agreement with GSK. Payment of this development milestone is due later this quarter. With that, let's turn the call over to Brian for our financial review.