ESMO Congress 2026

A necessary caveat on context first: the background references attached to this material are all environmental microbiology studies related to the Potomac River, including dissimilatory reduction of ferric iron and the isolate GS-15 in sediments ^[1][2], a chemical assay for microbially reducible iron ^[3] and its distribution in bottom sediments of the tidal freshwater river ^[4], as well as Potomac horse fever and other ehrlichial diseases ^[5] and the survival of Salmonella enteritidis in river water ^[6]. They share only the name with the oncology trial called POTOMAC and provide no clinical evidence. The materials also include no published phase III literature for durvalumab or BCG in NMIBC, so the prior evidence base is marked here as not disclosed, and this interpretation rests solely on the meeting data below.

What was presented at the meeting were two layers of data from the phase III POTOMAC trial. The first is the overall update in BCG-naïve high-risk NMIBC reported by Maria De Santos: adding durvalumab to BCG improved DFS (HR 0.68), with HR 0.48 in the T1 subgroup and cystectomy-free survival HR 0.45. The second is an exploratory (post hoc) analysis focused on papillary-only high-risk NMIBC: DFS HR 0.56 (95% CI 0.37–0.84), with 48-month DFS of 84% vs 74%; in the T1 subgroup, 48-month DFS of 85% vs 73%; high-risk recurrence 13% vs 20%, with fewer early high-risk events, BCG-unresponsive recurrences and cystectomies; cystectomy-free survival HR 0.59, an endpoint that includes death. On safety, the live posts disagree: some report Grade 3/4 TRAEs of 23% vs 3%, while another reports 34% vs 16%, pending confirmation from formal data.

Relative to prior understanding, these data quantify the benefit of adding durvalumab in the papillary-only population—a 44% reduction in the risk of recurrence/death—and show the strongest signal in the T1 subgroup (HR 0.48), with DFS and bladder-preservation endpoints pointing in the same direction, suggesting that fewer high-risk events and fewer cystectomies may occur together. Yet as Dr_Aggen asked, whether the incremental benefit is worth the added toxicity and treatment burden remains the key unresolved question.

The limitations should be stated plainly: the papillary-only results are a post hoc exploratory analysis rather than a prespecified primary endpoint; cystectomy-free survival counts death as an event; safety rates differ across the posts; and longer-term data such as overall survival were not disclosed.