TROPION-SWISH: New Phase IV Study Targets Side-Effect Risk in AstraZeneca and Daiichi Sankyo’s Dato-DXd

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

TROPION-SWISH: Daiichi Sankyo and AstraZeneca Launch Phase IV Study to Reduce Side Effects in Key Cancer Drugs

The TROPION-SWISH study, officially titled “A Phase IV, Open-Label, Single-Arm Study of Prophylaxis for Datopotamab Deruxtecan-related Stomatitis…,” aims to see whether a simple mouthwash routine can lower the rate and severity of mouth sores in patients receiving Datopotamab Deruxtecan (Dato-DXd) for advanced breast cancer or EGFR-mutated non-small cell lung cancer. The goal is to make treatment easier to tolerate, keep patients on therapy longer, and support the long-term commercial potential of Dato-DXd in two large oncology markets.

The study tests a steroid-based mouthwash (dexamethasone 0.5 mg/5 mL) used four times a day alongside standard treatment with Dato-DXd (also known as Datroway). The mouthwash is designed to prevent or reduce painful mouth inflammation, a known side effect of some targeted cancer drugs, without changing how the cancer drug itself is given. If effective, this low-cost intervention could become part of routine care for Dato-DXd patients.

This is an interventional Phase IV study with a single treatment group: all enrolled patients receive both Dato-DXd and the dexamethasone mouthwash. There is no randomization or placebo group, and no blinding; doctors and patients know exactly what is being given. The main purpose is preventive: to see how well this approach works to avoid mouth sores and whether it supports safer, more consistent use of Dato-DXd in real-world practice.

The study is listed as “Not yet recruiting,” with first submission and last update on January 21, 2026. These dates show that the protocol is finalized and the trial is preparing to open sites but has not yet started enrolling patients. Primary completion and final completion dates are not yet posted, which is typical for a new post-approval study; investors should view this as an early-stage, de-risking effort around an already commercial or late-stage asset rather than a binary approval event.

For investors, this update reinforces AstraZeneca (AZN) and Daiichi Sankyo’s (DSKYF) strategy to maximize the value of Dato-DXd by improving its side-effect profile and ease of use, rather than by changing the core drug. Successful prevention of stomatitis could support better adherence, longer duration of treatment, and broader physician confidence, all of which can lift revenue over time. In the wider oncology space, where competitors like Roche, Merck, and others are also strengthening supportive care around their cancer drugs, this kind of practical, patient-focused study is viewed positively but is unlikely to drive near-term stock spikes. Instead, it supports the long-term durability and quality of the Dato-DXd franchise and may modestly improve sentiment around both companies’ targeted oncology pipelines.

The TROPION-SWISH study is active in setup and recently updated, with further details available on the ClinicalTrials portal.

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