DS-9606 was supposed to be the first antibody-drug conjugate in Daiichi Sankyo’s line of anti-cancer assets to use a modified pyrrolobenzodiazepine payload.
Daiichi Sankyo has pulled the plug on its next-generation cancer therapy DS-9606, marking another setback in what has been a bumpy ride for its antibody-drug conjugate business.
“We’ve decided to discontinue its in-house development following a strategic portfolio review,” R&D chief Yuki Abe said of the asset during the company’s third- quarter 2025 earnings call. Abe spoke to investors in Japanese, but his remarks were translated in real-time for the benefit of international participants.
The company had validated the utility of DS-9606 in germ cell tumors, Abe said, noting that “there is room for making more development in that area.” However, “given the portfolio perspective, we decided not to continue the in-house development in this field.”
DS-9606 is a claudin-6-directed antibody-drug conjugate (ADC) that carries Daiichi Sankyo’s modified pyrrolobenzodiazepine (mPBD) payload, a cancer-killing chemical that binds to and disrupts tumor cell DNA. Daiichi Sankyo has planned several ADCs carrying mPBDs, and DS-9606 was supposed to be the first in this series.
Despite dropping DS-9606, Abe on the call insisted that the company has confirmed the usefulness of the mPBD platform and that “clinical programs will continue,” exploring other targets and carrier antibodies.
Daiichi Sankyo has also revealed Friday that it has delayed the readout from the Phase III Avanzar study, which was testing its breast cancer ADC Datroway in combination with AstraZeneca’s PD-L1 blocker Imfinzi for first-line non-small cell lung cancer (NSCLC). The company had originally expected to release data in the latter half of 2025, but has now pushed that back to the second half of this year.
Daiichi Sankyo has faced challenges with Datroway over the past couple of years.
In September 2024, the pharma partners rolled out a TROP2-based AI biomarker that, they claimed, would help identify NSCLC patients who are likely to benefit from Datroway. At the time, David Fredrickson, executive vice president of AstraZeneca’s oncology division, told Fierce Biotech that the new biomarker would apply to Avanzar.
The companies decided to turn to AI after Datroway in May 2024 failed a late-stage NSCLC study, unable to significantly boost overall survival in treated patients versus docetaxel. In September that year, shortly after unveiling its new biomarker, Datroway again hit a Phase III snag, failing to improve overall survival in patients with breast cancer.
Then, in November, the companies withdrew their approval application for Datroway in advanced or metastatic nonsquamous NSCLC and instead filed a new one, this time for EGFR-mutated NSCLC in patients who had undergone previous treatments. The FDA granted this approval in June last year. Datroway has also been approved for certain types of breast cancer.
