Intraperitoneal nivolumab (PD-1 blockade) yields 78% ascites control with minimal toxicity in GI/pancreaticobiliary cancers

Nivolumab (Opdivo), an anti–PD-1 immune checkpoint inhibitor, was administered intraperitoneally (IP) at 20 mg in 100 mL saline after paracentesis in a small, single-arm study of cytology-confirmed malignant ascites from advanced pancreatic (n=4), biliary tract (n=3), or gastric cancer (n=2) (n=9; NCT05745233). After a median 3 cycles (range 2–5), 7/9 patients (77.8%) had a clinical ascites response (less fluid and longer intervals between paracenteses); the only reported AE was grade 1 puncture-site tenderness, notably milder than historical IP immunostimulatory approaches like OK-432 in gastric malignant ascites where fever/abdominal pain are common despite similar response rates (~73%). In this setting, “standard care” is largely symptomatic (serial paracenteses ± diuretics/indwelling catheter), and prior locoregional biologics like catumaxomab improved time-to-next-paracentesis vs paracentesis alone (77 vs 13 days) but with cytokine-release-type toxicities and limited current availability—so an IP PD-1 approach that preserves tolerability could be meaningful if durability holds.