Q1 2025 Mersana Therapeutics Inc Earnings Call

In This Article:

Participants

Jason Fredette; Senior Vice President, Investor Relations & Corporate Communications; Mersana Therapeutics Inc

Martin Huber; President, Chief Executive Officer, Director; Mersana Therapeutics Inc

Brian Deschuytner; Chief Financial Officer, Chief Operating Officer, Senior Vice President; Mersana Therapeutics Inc

Tara Bancroft; Analyst; TD Cowen

Charles Zhu; Analyst; LifeSci Capital

Michael Schmidt; Analyst; Guggenheim Securities

Jonathan Chang; Analyst; Leerink Partners

Colleen Kusy; Senior Research Analyst; Robert W. Baird & Co Inc

Andy Hsieh; Analyst; William Blair

Karina Rabayeva; Analyst; Truist Securities

Presentation

Operator

Good morning and welcome to the Mersana Therapeutics first-quarter 2025 conference call. (Operator Instructions) I would now like to turn the call over to Mr. Jason Fredette, Senior Vice President, Investor Relations and Corporate Communications. Please proceed, sir.

Jason Fredette

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 in design, addressable market opportunities, anticipated clinical milestones and data presentations and cash runway.
Each of these forward-looking statements are 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 annual report on Form 10-K filed with the Securities and Exchange Commission on March 3, 2025 and in subsequent SEC filings. Our filings are available at sec.gov and on our website, mersana.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 Mersana's Chief Executive Officer, Dr. Marty Huber; and our Chief Operating Officer and Chief Financial Officer, Brian DeSchuytner.
With that, let me turn the call over to Marty to begin the discussion.

Martin Huber

Thank you, Jason, and good morning, everyone. Let's begin by touching on last week's announcement of Mersana's strategic restructuring and reprioritization plan. This plan includes several cost savings initiatives, among them are the reduction of about 55% of our workforce across functions, the elimination of our internal pipeline development efforts, a reduction of other research activities and a narrowing of our clinical development work with Emi-Le to focus on breast cancer.
We will continue supporting Phase 1 dose escalation work for XMT-2056 and our ongoing collaborations. Our main objective, however, was to extend our cash runway into mid-2026 to give us the opportunity to generate important objective response rate and durability data for Emi-Le from both of our ongoing Phase 1 dose expansion cohorts.
Many of our colleagues learned last week that they will be departing Mersana today, and others will be leaving in the near term. I would like to take a moment to thank them for all they have contributed to our programs and our patient-centric culture.
Now let's move on to a very timely topic. Earlier this morning at the ESMO Breast Cancer 2025 Congress in Munich, Dr. Erika Hamilton, who heads up breast cancer research at the Sarah Cannon Research Institute, presented updated clinical data for Emi-Le, our Dolasynthen B7-H4 ADC. The presentation primarily focused on preliminary time-to-event data from patients with triple-negative breast cancer, or TNBC, who are enrolled in our dose escalation and backfill cohorts. Safety and tolerability data in this population remain consistent with those previously reported with no new safety signals.
Now before getting into the clinical activity data, it may be helpful to share a little context upfront. First, it's worth noting that research, as shown B7-H4 expression, is a negative prognostic factor in various cancers, including in TNBC. In other words, clinical outcomes in patients with higher B7-H4 expression are generally worse than those for patients with lower expression. Additionally, it is helpful to know what the performance is for today's standard of care in late-line TNBC, namely single-agent chemotherapy. A key reference for this is ASCENT, Trodelvy's registrational trial in relapsed and refractory TNBC.
In that trial, patients receiving chemotherapy achieved an objective response rate, or ORR, of only 5%. The median progression-free survival, or PFS was about seven weeks and median overall survival, or OS was about seven months. Those data were from patients who were naive to topo-1 ADCs. Ultimately, we believe that this is the type of time-to-event data that a new agent would need to beat in a potential randomized pivotal trial in post topo-1 TNBC for full approval. And given these low bars, we believe such a randomized trial would not take much longer than a single arm trial.
With that, let's briefly recap the clinical activity data presented this morning. The presentation focused on evaluable patients with TNBC, who received intermediate doses of Emi-Le ranging from about 38 milligrams per meter squared up to about 67 milligrams per meter squared. Importantly, more than 80% of these TNBC patients had received a prior topo-1 ADC. Among those patients with B7-H4 low tumors who received four or fewer prior lines of treatment, the ORR was 0%. The median PFS was 6.4 weeks, and the median OS was 5.7 months.
But among those patients with what we have initially characterized as B7-H4 high tumors who received four fewer prior lines of therapy, the ORR was 29%. The median PFS was 16 weeks, and the median OS had not yet been reached as of the data cutoff of March 8.
As a reminder, our current dose expansion cohorts are only enrolling TNBC patients who received four or fewer prior lines of therapy, including at least one prior topo-1 ADC. While some patients with B7-H4 low tumor expression are being enrolled, our primary focus is on the B7-H4 high TNBC population. And so while the sample size from dose escalation of backfill is small, today's presentation sheds further light on why we continue to believe Emi-Le could represent a meaningful improvement over today's standard of care for patients with post topo-1 TNBC.
The ESMO breast presentation also contained an update on clinical activity observed across all tumor types in dose escalation backfill cohorts as of that data cutoff of March 8. And 8 of 26 evaluable patients with B7-H4 high tumor expression who received intermediate doses of Emi-Le achieved a confirmed response for an ORR of 31%.
This is an increase from the 23% ORR that was reported based upon our December 2024 data cutoff. Further details are contained in the ESMO breast presentation, which can be accessed on the publication sections of our website at mersana.com. We will be sharing some additional clinical data from dose escalation and backfill cohorts across all tumor types based on that March 8 data cutoff in an oral presentation at ASCO in a couple of weeks.
So where do we stand with our expansion work with Emi-Le? Well, we're making great progress. Again, in expansion, we are focusing on patients with TNBC who have received one to four prior lines of therapy, including at least one prior topo-1 ADC. Enrollment in our initial expansion cohort that is receiving 67.4 milligrams per meter square dose of Emi-Le every four weeks has advanced rapidly in 2025.
As a reminder, we amended our clinical trial protocol in the first quarter this year with the goal of mitigating proteinuria related dose delays we had seen at higher doses of Emi-Le. These proteinuria management guidelines have now been adopted at our clinical sites.
I'm also happy to share that we recently initiated and have progressed patient enrollment in our second TNBC expansion cohort. These patients are receiving a starting dose of 44.5 milligrams per meter squared of Emi-Le on days 1 and 8 of the first four-week cycle, followed by 80 milligrams per meter square every four weeks. We chose this regiment for a few reasons. First, all four of the evaluable B7-H4 high patients who received the 44.5 milligram per meter squared, day 1, day 8 dose every four weeks in dose escalation of backfill cohorts achieved tumor reductions of at least 30%.
Second, we believe our recent protocol amendment will enable us to maintain dose intensity and tolerability for our 80-milligram per meter squared Q4 dose. And third, our PK work showed that exposures for this regimen are distinct versus our 67-milligram per meter squared every four-week dose, which we believe may be helpful in the spirit of Project Optimus.
As we continue advancing our work and expansion, we are also witnessing a series of developments that could significantly expand the post topo-1 patient pool. Up until now, in the breast cancer space, topo-1 ADCs have only been approved for relapsed and refractory patients. But in recent months, there have been multiple positive Phase 3 readouts for topos in the frontline setting. Focusing specifically on the TNBC, as we've noted before, global TNBC revenues for Trodelvy in 2025 are projected to exceed $1 billion.
Just a few weeks ago, positive top line results were shared from ASCENT 4, a clinical trial for the combination of Trodelvy and KEYTRUDA in frontline TNBC. This readout may enable Trodelvy to become the new standard of care for first-line PD-L1 positive TNBC and with results from the Phase 3 ASCENT 3 trial in PD-L1 negative patients, also expected in the weeks ahead, we believe the post-topo-1 TNBC patient population could expand substantially.
In summary, we remain excited about Mersana's prospects. We're making great progress with expansion enrollment, and we are looking forward to sharing initial clinical data from expansion in the second half of this year.
With that, let's turn the call over to Brian for our financial review.