Magnusiomyces Capitatus Breakthrough Infection in Allogeneic Hematopoietic Cell Transplant Recipients Receiving Echinocandin Prophylaxis: Clinical Features, Management, and Structured Review of the Literature.

Magnusiomyces spp. infections are an uncommon but highly lethal emerging mycosis in immunocompromised patients, particularly those with hematologic malignancies and profound neutropenia. Data in the setting of allogeneic hematopoietic cell transplantation (allo-HCT) remain scarce. These infections typically occur early after transplantation as breakthrough events under antifungal prophylaxis and are associated with high mortality despite appropriate therapy. In this study, we report two concurrent cases from two Spanish transplant centers illustrating complementary clinical patterns, fulminant septic shock and progressive disseminated infection, both arising under echinocandin prophylaxis and both resulting in fatal outcomes, and provide a structured literature review derived from published individual cases to characterize this rare infection. Thirteen cases of Magnusiomyces infection in allo-HCT recipients (11 previously reported and 2 from the present study) were depicted, predominantly affecting adult male patients with hematologic malignancies. Infection occurred during profound neutropenia and most commonly as fungemia with frequent hematogenous dissemination to multiple organs. Despite heterogeneous antifungal prophylaxis, treatment outcomes were poor, with high early mortality (69%, 9/13). These findings highlight the aggressive nature of Magnusiomyces spp infections in allo-HCT and underscore the need for improved monitoring, preventive strategies, and more effective therapeutic approaches in this high-risk population.