Disitamab vedotin in locally advanced or metastatic extramammary Paget’s disease with HER2 high expression: A prospective, single-arm phase II trials (Formula-10)

Formula-10

Patient / Population Intervention / Exposure Comparison Outcome

In patients with HER2-high locally advanced or metastatic extramammary Paget's disease, disitamab vedotin achieved a high confirmed objective response rate with manageable toxicity.

N

27patients

Design

Prospective, open-label, single-arm phase 2 trial in adults with unresectable locally advanced or metastatic extramammary Paget's disease and HER2 IHC 2+ or 3+, all treated with disitamab vedotin until progression or intolerable toxicity (ChiCTR2500100703).

Endpoint

3-month objective response rate (ORR).

ResultInvestigator-assessed confirmed ORR 88.0% and DCR 100% in 25 evaluable patients, including 4 CR, 18 PR and 3 SD, at a median follow-up of 15.03 months. Median PFS 14.23 months (95% CI 9.87-20.37) and median DoR 10.90 months; median OS not mature. Grade ≥3 TRAEs occurred in 29.6%, including paraesthesia (14.8%) and fatigue (11.1%), with no treatment-related deaths. Common TRAEs were fatigue (88.9%), paraesthesia (81.5%), anorexia (55.6%) and alopecia (55.6%).

Tan X, Liu Z, Feng S, et al. Presented at ESMO Congress 2026, abstract LBA61, 25 October. Not yet published.

Discussion & critique

This single-arm, open-label phase 2 trial of 27 patients reports a high investigator-assessed confirmed response rate, but without a comparator the effect of the drug cannot be separated from patient selection. Responses were assessed by investigators rather than by blinded independent review, and the abstract does not make clear whether the reported ORR is the prespecified 3-month endpoint. Overall survival is not mature, and the efficacy analysis covers only 25 evaluable patients, so progression-free survival and duration of response estimates rest on very few patients. Only a minority had received prior chemotherapy, and quality of life, a listed secondary endpoint, is not reported.