Daiichi Sankyo’s ADC Push in Gastroesophageal Cancer: What Substudy 06D Means for Investors

Daiichi Sankyo Company (DSKYF) announced an update on their ongoing clinical study.

Study Overview: Substudy 06D, formally titled “A Phase 1/2 Open-Label, Umbrella Platform Design Study to Evaluate the Safety and Efficacy of Investigational Agents in Combination With Standard of Care Treatments as the Second-Line Treatment of Participants With Advanced/Metastatic Gastroesophageal Adenocarcinoma: Substudy 06D,” is testing new drug combinations for advanced stomach and esophageal cancers after first-line therapy has failed. The goal is to see if adding novel antibody–drug conjugates to current standard care can improve outcomes versus existing regimens, which would be important for both patient care and the oncology portfolios of Merck and its collaborator Daiichi Sankyo.

Intervention/Treatment: The study compares three combination treatments. The control arm uses ramucirumab plus paclitaxel, a standard second-line option in this cancer setting. One experimental arm adds sacituzumab tirumotecan (MK-2870), an antibody–drug conjugate designed to deliver chemotherapy directly to cancer cells, on top of paclitaxel. The other experimental arm combines HER3-DXd, another targeted antibody–drug conjugate from Daiichi Sankyo’s pipeline, with ramucirumab. All drugs are given by intravenous infusion.

Study Design: This is an interventional Phase 1/2 trial with participants randomly assigned to one of the treatment arms. The model is parallel, meaning each group receives its assigned regimen in the same period without crossover. The study is open-label, so patients and doctors know which treatment is given, but the outcome assessors are masked to reduce bias in measuring results. The primary aim is treatment-focused, looking mainly at safety and how well the different combinations control the cancer, rather than testing a strict statistical hypothesis.

Study Timeline: The study was first submitted on May 31, 2024, marking the formal launch of this substudy within the broader platform program. It is currently listed as recruiting, showing that enrollment is active and key data are still ahead. The last update was submitted on December 22, 2025, signaling that the protocol and status have been recently reviewed and refreshed, which is important for investors tracking development progress and any design tweaks that may affect timelines and risk.

Market Implications: For Daiichi Sankyo (DSKYF), this update underscores continued investment and collaboration in antibody–drug conjugates, a field where the company is already seen as a leader. Positive signals from sacituzumab tirumotecan or HER3-DXd in this second-line gastroesophageal setting could strengthen confidence in its broader ADC platform, support higher long-term revenue expectations, and improve sentiment toward its oncology pipeline. For Merck, success would add to its checkpoint and combo strategy, but the value uplift for Daiichi Sankyo is more pipeline-leveraged given its role as ADC developer. Competitors like AstraZeneca and Seagen/Pfizer are also pushing ADCs in solid tumors, so any early efficacy or safety advantages could shift attention and capital flows toward Daiichi Sankyo’s technology. While the trial is still early and no results are available, the active recruiting status and recent update suggest steady execution, which may be viewed as a modest near-term positive for pipeline visibility and a medium- to long-term driver of stock performance if later data are strong.

The study remains ongoing and recently updated, with further details and future results to be made available on the ClinicalTrials portal.

To learn more about DSKYF’s potential, visit the Daiichi Sankyo Company drug pipeline page.