ProKidney Cuts Phase 3 Power Assumption and Cohort Size for Third Time in Three Months
Company Background
ProKidney Corp. is a clinical-stage cell therapy company developing rilparencel, an autologous kidney cell therapy, for patients with Stage 3b/4 chronic kidney disease and type 2 diabetes. Rilparencel carries the FDA's Regenerative Medicine Advanced Therapy designation and is the only cell therapy currently in a Phase 3 study for that indication. The company has no approved products and generates minimal revenue — $226,000 in the first quarter of 2026.
The company's entire near-term value rests on its pivotal Phase 3 PROACT 1 trial (REGEN-006). ProKidney entered 2026 on what appeared to be solid footing: in July 2025, Phase 2 REGEN-007 data showed a statistically significant 4.6 mL/min/1.73m² improvement in eGFR slope in Group 1, well above the FDA-agreed minimum effect size of 1.5 mL/min/1.73m². That same month, a Type B meeting confirmed eGFR slope as the primary surrogate endpoint for accelerated approval. ProKidney had roughly $375 million in market capitalization and $224.9 million in cash as of March 31, 2026.
Since late 2025, however, ProKidney has repeatedly revised the design parameters of PROACT 1 downward. Total planned enrollment was cut from approximately 685 subjects to approximately 470 in February 2026. The size of the accelerated approval efficacy cohort was listed at approximately 360 patients in the March 2026 full-year earnings release and has now been reduced again to approximately 320. The statistical power assumption for the surrogate endpoint analysis has also been revised.
What Was Disclosed
On May 15, 2026, ProKidney filed an 8-K disclosing first-quarter 2026 financial results, an updated investor presentation, and — in a separate Item 8.01 — a one-sentence update to the statistical design of PROACT 1: the powering assumption for the surrogate endpoint (eGFR slope) analysis has been revised to 80%. The filing also quantifies the current power profile: 80% power to detect a 1.5 mL/min/1.73m² effect size (the FDA's agreed minimum threshold) and 90% power to detect a 1.75 mL/min/1.73m² effect. The investor presentation accompanying the filing shows the accelerated approval analysis cohort has been reduced from approximately 360 patients (as stated in the March 18, 2026 full-year earnings release) to approximately 320. The confirmatory composite endpoint analysis target remains at approximately 470 subjects. The BLA submission timeline has also shifted: the March 2026 milestones table listed Q4 2027; the May 2026 investor presentation now states Early 2028.
Why It Matters
The significance of the 80% power revision depends on what was assumed before. The filing does not state the prior power assumption. What it does reveal — through the combination of reducing the analysis cohort from ~360 to ~320 patients and setting 80% power at the FDA's minimum acceptable effect size of 1.5 mL/min/1.73m² — is that the internal model for the expected Phase 3 effect size has moved closer to the regulatory floor. In a Phase 3 trial powered at exactly 80% to detect the minimum acceptable threshold, any effect somewhat weaker than that floor would carry a meaningful probability of a failed primary endpoint. The Phase 2 Group 1 signal of 4.6 mL/min/1.73m² was substantially larger, but Phase 2 trials regularly overestimate effect sizes, and the PROACT 1 patient population has been progressively refined.
This is the third sequential downward revision to PROACT 1 design parameters in roughly three months. In February 2026, total enrollment was cut from approximately 685 to approximately 470 subjects. In the March 2026 full-year release, the accelerated approval cohort was cited at approximately 360 patients. The May 2026 filing reduces that figure further to approximately 320 and explicitly states the power assumption has been updated to 80%. Each change on its own might reflect normal trial optimization; the pattern across three filings is harder to dismiss.
ProKidney's financial position provides limited cushion. Operating cash used in Q1 2026 was $41.7 million, up from $29.6 million in Q1 2025, driven primarily by increased PROACT 1 clinical and manufacturing costs. At the March 31, 2026 cash balance of $224.9 million, the company projects a runway into mid-2027 — which is exactly when pivotal topline data are expected. There is no material financial buffer between the data readout and the end of runway as currently modeled, meaning a failed or ambiguous readout would require additional capital.