• Additional data from DESTINY-Breast11, DESTINY-Breast05, DESTINY-Breast09, DESTINY-Breast03 and TROPION-Breast02 reinforce practice-changing results of ENHERTU^® and DATROWAY^® across a broad spectrum of patients with breast cancer
• Trials-in-progress across breast cancer portfolio of Daiichi Sankyo demonstrate company’s commitment to creating new standards of care
• Science & Technology Day to be held following SABCS to discuss R&D and oncology business updates

TOKYO & BASKING RIDGE, N.J.--(BUSINESS WIRE)--Dec. 8, 2025-- Daiichi Sankyo (TSE: 4568) will present new breast cancer clinical research across its DXd antibody drug conjugate (ADC) portfolio from more than 30 abstracts at the 2025 San Antonio Breast Cancer Symposium (#SABCS25), which include four rapid fire mini-oral sessions and other presentations from five landmark trials of ENHERTU^® (trastuzumab deruxtecan) and DATROWAY^® (datopotamab deruxtecan) across a broad spectrum of breast cancer.

Four rapid fire mini-oral sessions will feature ENHERTU data in the curative-intent and metastatic settings of HER2 positive breast cancer, including two presentations from the DESTINY-Breast11 phase 3 trial highlighting patient reported outcomes (RF6-06) and further safety analyses (RF6-02) of ENHERTU followed by paclitaxel, trastuzumab and pertuzumab (THP) compared to dose-dense doxorubicin and cyclophosphamide followed by THP (ddAC-THP) in the neoadjuvant setting (before surgery) in patients with high-risk, locally advanced HER2 positive early-stage breast cancer. Additional efficacy and safety data (RF6-01) from the DESTINY-Breast05 phase 3 trial comparing ENHERTU to trastuzumab emtansine (T-DM1) as a post-neoadjuvant (after surgery) therapy in patients with high-risk HER2 positive early breast cancer with residual invasive disease in the breast and/or axillary lymph nodes also will be highlighted.

The fourth rapid fire presentation will feature patient reported outcomes (RF6-07) from the ENHERTU plus pertuzumab arm of the DESTINY-Breast09 phase 3 trial as a first-line treatment of HER2 positive metastatic breast cancer. Interim results from DESTINY-Breast09 were recently published in The New England Journal of Medicine, marking the eighth pivotal trial of ENHERTU to be published in the prestigious journal.

Additional updates from two other landmark breast cancer trials include poster presentations featuring the final analysis and five-year follow-up of efficacy and safety data (PS5-01-30) from the DESTINY-Breast03 phase 3 trial comparing ENHERTU versus T-DM1 as a second-line treatment of HER2 positive metastatic breast cancer, and further safety analysis (PS5-03-05) from the TROPION-Breast02 phase 3 trial of DATROWAY, the first trial ever to demonstrate a significant improvement in overall survival compared to chemotherapy as first-line treatment for patients with locally recurrent inoperable or metastatic triple negative breast cancer (TNBC) for whom immunotherapy is not an option.

“Our latest research across these five landmark trials demonstrate how the DXd antibody drug conjugate portfolio of Daiichi Sankyo continues to potentially transform standards of care for patients with breast cancer,” said Ken Takeshita, MD, Global Head, R&D, Daiichi Sankyo. “We remain committed to following the science and collaborating with the breast cancer community to create innovative medicines that advance the treatment of breast cancer.”

Additional data from the DESTINY clinical trial program to be highlighted in poster presentations at SABCS include an exploratory post-hoc subgroup analysis by hormone receptor status from the DESTINY-Breast12 phase 3b/4 trial (PS5-01-27) of ENHERTU in patients with HER2 positive metastatic breast cancer and brain metastases; the final results from the ENHERTU monotherapy and ENHERTU plus pertuzumab arms of the DESTINY-Breast07 phase 1b/2 trial (PS5-01-14) in patients with previously untreated HER2 positive metastatic breast cancer; and, initial characteristics of first enrolled patients from the DESTINY Breast Respond HER2 Low Europe non-interventional study (PS5-08-14) of ENHERTU in HER2 low metastatic breast cancer.

Collaborations Supporting Innovation in Breast Cancer Research
Additional data presented at SABCS include results from four externally sponsored trials across the DXd ADC pipeline of Daiichi Sankyo. Two spotlight poster presentations will report interim results from the HALLOW prospective observational trial (PD13-11) evaluating the efficacy and safety of ENHERTU in patients with HER2 low (IHC 1+ or 2+/ISH-) metastatic breast cancer with and without active brain metastases in Japan, and a post-hoc pooled efficacy analysis (PD13-10) from the TUXEDO-3 phase 2 trial of patritumab deruxtecan (HER3-DXd) in patients with HER2 positive metastatic breast cancer and active brain metastases or leptomeningeal disease previously treated with ENHERTU. Results from cohorts 1 and cohorts 2 of the TUXEDO-3 trial were recently published in The Lancet Oncology and results from cohort 3 were published in Nature Medicine.

Two poster presentations will report on the intracranial and/or extracranial activity of ENHERTU and DATROWAY. A translational ctDNA analysis of intracranial and extracranial activity (PS2-08-20) of ENHERTU from the DEBBRAH phase 2 trial in patients with HER2 positive and HER2 low breast cancer with leptomeningeal disease will be highlighted, as well as results of intracranial activity (PS1-09-02) of DATROWAY from the DATO-BASE phase 2 trial in patients with HER2 negative breast cancer with leptomeningeal disease.

Trials-in-Progress Across Breast Cancer Portfolio of Daiichi Sankyo
Several trials-in-progress poster presentations at SABCS further highlight research underway to address a broad spectrum of unmet needs for patients with breast cancer.

Additional externally sponsored trials for ENHERTU and DATROWAY include the PONTIAC phase 2 trial (PS5-07-15) evaluating ENHERTU versus CDK4/6 inhibitor-based endocrine therapy as a first-line treatment of non-luminal HR positive, HER2 low and HER2 ultralow advanced breast cancer; a phase 1b trial (PS5-09-22) evaluating ENHERTU in combination with valemetostat, an EZH1/2 inhibitor, in patients with HER2 low, HER2 ultralow and HER2 null metastatic breast cancer; and the TROPION-Breast06 phase 3b trial (PS5-07-21) of DATROWAY in patients with HR positive, HER2 IHC 0 inoperable or metastatic breast cancer refractory to endocrine therapy.

Three additional trials-in-progress from the HERTHENA clinical development program of patritumab deruxtecan (HER3-DXd) also will be highlighted. These include the HERTHENA-Breast04 phase 3 trial (PS5-07-22) evaluating patritumab deruxtecan versus physician’s choice of treatment in patients with HR positive, HER2 negative unresectable locally advanced or metastatic breast cancer; the HERTHENA-Breast03 phase 2 trial (PS5-12-21) evaluating neoadjuvant patritumab deruxtecan plus pembrolizumab before or after pembrolizumab plus chemotherapy in patients with high-risk early-stage TNBC or HR low positive/HER2 negative breast cancer; and, the HERTHENA-Breast01 phase 1b/2 trial (PS5-12-23) evaluating patritumab deruxtecan in combination with HER2 targeted agents in patients with HER2 positive unresectable locally advanced or metastatic breast cancer.

Science & Technology Day
Daiichi Sankyo will hold its annual Science & Technology Day for investors on Monday, December 15, 2025, from 5:30 to 7:30 pm ET / Tuesday, December 16, 2025, from 7:30 – 9:30 am JST. Executives from Daiichi Sankyo will provide an update on R&D, business and manufacturing developments across the portfolio.

Daiichi Sankyo Presentation Highlights at SABCS

About the ADC Portfolio of Daiichi Sankyo
The Daiichi Sankyo ADC portfolio consists of eight ADCs in clinical development crafted from ADC technology discovered in-house by Daiichi Sankyo.

The DXd ADC Technology platform of Daiichi Sankyo consists of six ADCs in clinical development where each ADC is comprised of a monoclonal antibody attached to a number of topoisomerase I inhibitor payloads (an exatecan derivative, DXd) via tetrapeptide-based cleavable linkers. The DXd ADCs include ENHERTU^® and DATROWAY^®, which are being jointly developed and commercialized globally with AstraZeneca, and ifinatamab deruxtecan (I-DXd), raludotatug deruxtecan (R-DXd) and patritumab deruxtecan (HER3-DXd), which are being jointly developed and commercialized globally with Merck & Co., Inc, Rahway, NJ, USA. DS-3939 is being developed by Daiichi Sankyo.

Additional ADCs being developed by Daiichi Sankyo include DS-9606, which consists of a monoclonal antibody attached to a modified pyrrolobenzodiazepine (PBD) payload and DS3610, which consists of an antibody attached to a novel immunomodulatory payload that acts as an agonist of STING.

Ifinatamab deruxtecan, raludotatug deruxtecan, patritumab deruxtecan, DS-3939, DS-9606 and DS3610 are investigational medicines that have not been approved for any indication in any country. Safety and efficacy have not been established.

About Daiichi Sankyo
Daiichi Sankyo is an innovative global healthcare company contributing to the sustainable development of society that discovers, develops and delivers new standards of care to enrich the quality of life around the world. With more than 120 years of experience, Daiichi Sankyo leverages its world-class science and technology to create new modalities and innovative medicines for people with cancer, cardiovascular and other diseases with high unmet medical needs. For more information, please visit www.daiichisankyo.com.

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Source: Daiichi Sankyo