X4 Pharmaceuticals gets FDA agreement to cut 4WARD trial size to 126 patients

X4 Pharmaceuticals announced on September 8, 2026 that it received a positive outcome from a Type C Meeting with the FDA concerning its global Phase 3 trial "4WARD," which is testing mavorixafor in chronic neutropenia patients. The meeting was held to align on a revised sample size and associated statistical power, as well as the size of the safety database needed to support a supplemental new drug application for mavorixafor in chronic neutropenia.¹

The FDA agreed with the company's analysis that cutting the trial's sample size from 176 to 126 participants still maintains adequate power for the co-primary endpoints, which measure reduction in annualized infection rate and positive absolute neutrophil count response.¹ The FDA also indicated that the company's proposed safety database size would be acceptable to support a potential sNDA.¹

Executive Chairman Adam Craig said a rigorous re-examination of the statistical plan led the company to conclude the trial had been overpowered, allowing the reduction to 126 participants while preserving statistical power for the co-primary endpoints.¹ He said the company now expects, with support from its new clinical research organization, to finish enrolling 4WARD by the end of this year and to have topline results available during the first half of 2028.¹

The 4WARD trial is a global, pivotal Phase 3 study testing the once-daily oral drug mavorixafor, given with or without G-CSF, in patients age 12 and older with congenital, acquired primary autoimmune, or idiopathic chronic neutropenia who have had at least two serious or recurrent infections in the past year, and it is designed as a 52-week randomized, double-blind, placebo-controlled, multicenter study now aiming to enroll 126 patients.¹

The company noted that the FDA's Type C meeting feedback is not binding, and the agency could take a different position when reviewing any eventual sNDA.¹