Merck’s KEYNOTE-B96 trial signals survival benefit in platinum-resistant ovarian cancer, but MRK stock dips

Merck & Co Inc (NYSE: MRK) announced on October 16 that KEYTRUDA (pembrolizumab), its flagship anti-PD-1 therapy, achieved a key secondary endpoint of overall survival (OS) in the Phase 3 KEYNOTE-B96 trial for patients with platinum-resistant recurrent ovarian cancer, including those beyond the PD-L1 positive subgroup. Despite this first-of-its-kind immunotherapy success in a hard-to-treat setting, Merck shares closed 0.23% lower at USD 83.92, dipping further to USD 83.62 in after-hours trading, as investors awaited detailed efficacy data and regulatory clarity before revaluing MRK stock.

The KEYNOTE-B96 study is the first randomized clinical trial involving an immune checkpoint inhibitor regimen to demonstrate statistically significant overall survival improvement in this highly challenging population. Yet, markets appeared more cautious than celebratory, weighing Merck’s longer-term immuno-oncology strategy against near-term earnings risks and broader sector sentiment.

What is the significance of the KEYNOTE-B96 trial results for Merck’s immunotherapy portfolio?

The KEYNOTE-B96 study, also referred to as ENGOT-ov65, evaluated KEYTRUDA (pembrolizumab)—in combination with paclitaxel chemotherapy, with or without bevacizumab, in patients diagnosed with platinum-resistant recurrent ovarian cancer. The trial compared this combination to a control arm using placebo plus chemotherapy with or without bevacizumab.

While Merck had previously confirmed that the trial had met its primary endpoint of progression-free survival (PFS), as well as an earlier OS benchmark in the PD-L1 expressing subgroup, the October 16 announcement confirmed that the overall survival benefit extended to all comers, not just biomarker-positive patients. According to the company, the final analysis showed that the KEYTRUDA-based regimen achieved both statistical and clinical significance in improving OS across the entire study population.

This development could set a new benchmark in treating platinum-resistant ovarian cancer—a category where therapeutic options remain few and median survival outcomes are poor. The safety profile of KEYTRUDA in this trial remained consistent with past data, and no new adverse safety signals were identified. Full data will be presented at an upcoming European Society for Medical Oncology (ESMO) Congress in 2025.

Why are investors cautious despite positive trial results in a high-unmet-need cancer population?

Despite the breakthrough nature of the data, Merck’s stock performance remained muted, with shares declining slightly during the day and further in after-hours trading. Market reaction suggests that investors may be adopting a “show me more” stance for several reasons. Most notably, KEYTRUDA is not yet approved for ovarian cancer, and Merck has not publicly announced any plans to file for regulatory approval based on this trial.

Secondly, the company has not released detailed statistical data such as hazard ratios, median OS benefit, or subgroup analyses, which are typically necessary to influence oncologist adoption, payer confidence, and investor valuation models. Without these details, the Street is treating the announcement as promising but incomplete.

Analysts also note that investor focus remains on Merck’s broader oncology and pipeline execution, particularly with respect to near-term revenue visibility, biosimilar threats to KEYTRUDA post-2028, and expansion into earlier-stage cancers. Until Merck provides further commercial clarity or files with the FDA for a label expansion, institutional sentiment around MRK stock may remain defensive.

How does this trial fit into Merck’s strategy for women’s cancers and gynecologic oncology?

Merck has made significant investments in the development of therapies for women’s cancers, particularly in ovarian, cervical, and endometrial malignancies. As part of this strategy, the American pharmaceutical giant is conducting over 20 clinical trials across nearly 20,000 patients globally. These studies are aimed at advancing earlier-stage interventions, exploring combination therapies, and extending immuno-oncology into indications that have historically resisted checkpoint inhibitors.

While KEYTRUDA is not approved for ovarian cancer, Merck co-markets LYNPARZA (olaparib) with AstraZeneca, which is FDA-approved for several ovarian cancer indications including maintenance therapy in BRCA-mutated and HRD-positive advanced cases. However, LYNPARZA has not demonstrated efficacy in platinum-resistant recurrent ovarian cancer, leaving a significant gap in Merck’s women’s cancer portfolio that KEYNOTE-B96 may now help address.

The company is also working with Daiichi Sankyo on raludotatug deruxtecan (R-DXd), an antibody-drug conjugate that recently received Breakthrough Therapy Designation from the U.S. FDA for platinum-resistant ovarian cancer patients with CDH6 expression. That designation was based on early-stage data from the REJOICE-Ovarian01 trial, and final results from that study will also be presented at ESMO 2025.

Taken together, these programs position Merck to build a more comprehensive women’s oncology portfolio that could span the treatment continuum—from front-line maintenance to heavily pretreated, biomarker-unselected patients.

What is the commercial and clinical importance of targeting platinum-resistant ovarian cancer?

Platinum-resistant ovarian cancer remains one of the most challenging subtypes to treat in modern oncology. Most advanced-stage ovarian cancer patients receive platinum-based chemotherapy as part of their first-line treatment. However, between 70% to 80% of patients relapse, and approximately 25% develop platinum resistance within six months, a condition defined as primary platinum-resistant ovarian cancer.

Patients with this condition face poor survival prospects and are often excluded from immunotherapy trials due to historically poor responses. Globally, over 324,000 new ovarian cancer cases and 207,000 deaths were recorded in 2022. By 2040, the global incidence is expected to increase by 42%, intensifying the demand for novel therapeutic interventions.

Against this backdrop, KEYNOTE-B96 stands out. It is the first study to demonstrate OS benefit from a checkpoint inhibitor-based regimen in an all-comers setting for platinum-resistant ovarian cancer. Clinically, this could set a new standard. Commercially, it offers Merck a foothold in a space with limited competitive pressure, especially if it can gain FDA approval and establish coverage frameworks with insurers.

How are institutional investors viewing Merck’s stock in light of the KEYNOTE-B96 readout?

Institutional sentiment remains neutral to mildly optimistic. While the scientific and clinical communities are likely to applaud the study design and efficacy signals, portfolio managers are treating the announcement as a medium- to long-term catalyst, rather than a near-term valuation driver. Options trading volumes have not shown a significant spike, and fund flows into MRK have remained flat.

Analysts generally agree that Merck needs more than incremental clinical wins to excite equity markets at its current scale. The company’s near-term prospects remain tied to KEYTRUDA’s existing labels, pipeline updates in cardiometabolic programs, and business development activities in antibody-drug conjugates, vaccines, and oncology diagnostics.

In the current macro environment—marked by high interest rates, pricing scrutiny on branded therapies, and geopolitical supply chain risks—MRK is increasingly being viewed as a defensive large-cap healthcare stock, rather than a high-growth biotech play.

What are the next catalysts for Merck and how might this trial impact future regulatory filings?

Merck has not confirmed if it plans to submit the KEYNOTE-B96 data to the FDA for a new indication approval. However, the statistically significant OS results in all comers provide a strong rationale for doing so. The presentation at ESMO 2025 is expected to offer the clarity that investors and regulators are waiting for. If the hazard ratio for OS meets or exceeds expectations and toxicity remains manageable, analysts believe a regulatory filing is plausible in 2026.

Beyond ovarian cancer, Merck’s pipeline includes further development of KEYTRUDA and LYNPARZA across endometrial, cervical, and triple-negative breast cancer, as well as broader combinations with ADCs and next-generation immune modulators. These efforts could serve as risk diversification as Merck prepares for KEYTRUDA’s patent expiration in major markets post-2028.

The company’s strategic partnership with Daiichi Sankyo on ADCs is also expected to deliver new trial readouts in the coming quarters, potentially providing the next wave of investor catalysts.

What are the key takeaways from merck’s KEYNOTE-B96 survival data and MRK stock response?

• Merck’s KEYNOTE-B96 trial became the first to show overall survival benefit with an immune checkpoint inhibitor in platinum-resistant recurrent ovarian cancer, extending previous progression-free survival results to all comers.

• The KEYTRUDA-based regimen demonstrated a statistically significant and clinically meaningful survival improvement, positioning Merck for potential regulatory filings in a high unmet need segment.

• The stock closed down 0.23% on October 16, with after-hours trading also reflecting cautious investor sentiment, likely due to the absence of numerical data and no immediate FDA filing announcement.

• KEYTRUDA is not yet approved for ovarian cancer, and full results from the trial will be presented at ESMO Congress 2025, making this a medium-term catalyst rather than a near-term valuation driver.

• The trial adds momentum to Merck’s broader women’s oncology strategy, which also includes LYNPARZA and its antibody-drug conjugate partnership with Daiichi Sankyo.

• Analysts and institutional investors are likely to remain in “wait-and-see” mode until more granular data is released and Merck signals whether it intends to pursue a label expansion.

• The platinum-resistant ovarian cancer space is difficult to treat and largely underserved, and if approved, KEYTRUDA’s new indication could provide both clinical impact and a modest commercial upside for Merck.

• Future investor watchpoints include Merck’s Q3 earnings, potential FDA submission updates, and companion readouts from its broader gynecologic cancer portfolio.