What You Should Know

  • Early data show the cancer drug mocertatug rezetecan (Mo‑Rez) delivering response rates above 60% in patients with recurrent ovarian and endometrial cancers.
  • The Phase 1 BEHOLD-1 clinical trial, which is evaluating Mo‑Rez, a B7‑H4–targeted antibody‑drug conjugate, is considered a major step forward among experts.
  • The trial’s early results highlight the promise of Mo-Rez since the standard treatment for recurrent ovarian and endometrial cancer yields modest results in comparison, more specifically, an objective response rate of “5 to 15%,” says Dr. Sarah Taylor, Director of Obstetrics, Gynecology and Reproductive Sciences at the University of Pittsburgh and Magee-Womens Hospital of UPMC.
  • Experts say early results from BEHOLD-1 offer real hope for patients with high unmet need, leading Dr. Bhavana Pothuri, director of Gynecologic Oncology Clinical Trials at NYU Langone Health, to eagerly await “the phase 3 trials in both ovarian and endometrial cancer in hopes of bringing Mo‑Rez quickly to patients across the world.”

For oncologists who focus on ovarian and endometrial cancer, there are not enough potentially game-changing trials. The medication studied in the BEHOLD-1 clinical trial could well fall into that category as later stage trials build on the data just released at the 2026 SGO meeting. These results showed the experimental drug mocertatug rezetecan (Mo-Rez) achieving response rates above 60% in recurrent ovarian and endometrial cancers.

“We are excited to see this drug tested further, as it may be a great new option for patients with a high unmet need,” Dr. Jessica Parker of Indiana University’s Melvin and Bren Simon Comprehensive Cancer Center, tells SurvivorNet.

The BEHOLD-1 trial tests Mo-Rez, a B7-H4–targeted antibody-drug conjugate (ADC), in patients with advanced solid tumors, including platinum-resistant ovarian and endometrial cancers.

Although the phase 1 trial results are early, they outperform the standard of care for platinum-resistant ovarian cancer, and a new benchmark could be established if ongoing trial data follow this promising path.

“While a longer follow‑up is needed to determine whether the high response rates observed in BEHOLD‑1 will translate into durable survival benefits, these results represent exceptionally encouraging phase I data and suggest that B7‑H4–targeted ADCs may define a new efficacy benchmark for heavily pretreated gynecologic cancers,” Dr. Sarah Taylor, Director of Obstetrics, Gynecology and Reproductive Sciences at the University of Pittsburgh and Magee-Womens Hospital of UPMC tells SurvivorNet.

She explains that B7‑H4, a co‑inhibitory immune checkpoint ligand, is highly expressed across gynecologic cancers, especially ovarian and endometrial tumors, while showing minimal expression in normal tissues, making it an appealing therapeutic target.

Mo‑Rez pairs an anti–B7‑H4 antibody with a topoisomerase I inhibitor payload, a design intended to deliver potent chemotherapy directly to cancer cells.

Strong Early Signals In a Difficult‑to‑Treat Population

According to data presented at the 2026 Society of Gynecologic Oncology (SGO) Annual Meeting, the drug manufacturer of mocertatug rezetecan, GSK, highlighted clinical trial progress in Puerto Rico this year.

Mo‑Rez demonstrated notably high response rates in heavily pretreated patients.

According to data presented at SGO, GSK reported that at the highest doses tested:

  • 62% of patients with platinum‑resistant ovarian cancer achieved confirmed objective responses.
  • 67% of patients with recurrent or advanced endometrial cancer responded to treatment

“Platinum‑resistant ovarian cancer and advanced endometrial cancer can be difficult to treat with overall low response rates to later‑line therapies,” Dr. Parker said.

The most common side effect reported was nausea, and overall toxicity was described as manageable.

“The toxicities reported were not meaningfully different from active agents in the same space,” says Dr. Whitfield Growdon, a Gynecologic Oncologist at NYU Langone, who tells SurvivorNet.

Dr. Bhavana Pothuri, director of Gynecologic Oncology Clinical Trials at NYU Langone Health, emphasizes that these responses occurred in patients who had already received a median of two prior lines of therapy, adding that Mo‑Rez “appears well‑tolerated with a low discontinuation rate.”

“These are very encouraging data for the evolving landscape of antibody drug conjugates in Gynecologic cancer treatment,” Dr. Sarah Lynam, Co-Leader, Gynecology Disease Team at UH Seidman Cancer Center, tells SurvivorNet.

“This agent is of particular interest as we explore the role of B7H4-directed therapies and their immunological effects in ovarian and endometrial cancers, especially among patients previously treated with immunotherapy,” Dr. Lynam adds.

How Mo‑Rez Compares to Current Benchmarks

Dr. Taylor notes that standard single‑agent chemotherapy in these settings typically yields objective response rates of only 5–15%.

Recent advances have raised the bar:

  • Mirvetuximab soravtansine (Elahere) achieved a 42.3% response rate in FRα‑high platinum‑resistant ovarian cancer in the phase III MIRASOL trial.
  • In endometrial cancer, lenvatinib + pembrolizumab, a current standard, produced 30–35% response rates in previously treated advanced disease (KEYNOTE‑775).

Against that backdrop, the early Mo‑Rez data stand out.

“Treatment of platinum-resistant ovarian cancer is one of our most difficult scenarios,” and the early results are giving oncologists “a sense of hope for the future,” Dr. Amy Armstrong, Division Chief, Gynecologic Oncology at UH Seidman Cancer Center.

What Comes Next

“These results represent exceptionally encouraging phase I data and suggest that B7‑H4–targeted ADCs may define a new efficacy benchmark for heavily pretreated gynecologic cancers,” Dr. Taylor says.

Clinicians across many cancer institutions echo the optimism Mo-Rez provides while stressing the need for continued follow‑up in future clinical trial phases.