First reported case of disseminated Cunninghamella phaeospora infection with multidrug resistance in acute myeloid leukemia.

Mucormycosis is a severe mold infection primarily affecting immunocompromised patients. Neutropenia, steroid use, hyperglycemia, and diabetes are recognized as significant risk factors. Cunninghamella species are rare pathogenic fungi associated with high mortality rates and multidrug resistance. However, there have been no reports of C. phaeospora being identified as the causative agent of clinical infection. We report a case of a 71-year-old man who developed right middle lobe pneumonia during salvage induction therapy for relapsed acute myeloid leukemia. Based on the clinical course, mucormycosis was suspected, and antifungal therapy was initiated with isavuconazole (200 mg every 8 hours for six doses, followed by 200 mg daily) and later switched to liposomal amphotericin B (5 mg/kg/day). Despite these interventions, the patient's respiratory failure progressed, culminating in a fatal hemorrhagic infarction of the right lung. An autopsy revealed invasive fungal involvement in multiple organs, including the lungs and liver. Genetic identification of the isolated fungi demonstrated C. phaeospora, confirming disseminated C. phaeospora infection. Susceptibility testing showed high Minimum Inhibition Concentrations/Minimum Effective Concentrations to all tested antifungal agents. This is the first reported case of disseminated infection caused by C. phaeospora with multidrug resistance. This case highlights the diagnostic and therapeutic challenges associated with rare pathogenic fungi. It underscores the importance of early identification of Mucorales, including susceptibility testing, to optimize antifungal therapy and consider appropriate surgical interventions. Further research is required to elucidate the mechanisms of antifungal resistance and clinical characteristics of C. phaeospora.