Breakthrough zygomycosis on posaconazole prophylaxis after allogeneic stem cell transplantation.

Antifungal prophylaxis with posaconazole (POS) has been shown to decrease the mortality associated with invasive fungal infections in high-risk patients. We report on a patient, with severe graft-versus-host disease after allogeneic stem cell transplantation, who developed proven pneumonia due to Rhizopus microsporus after 40 days of POS prophylaxis (fasting serum levels: 691-904 ng/mL). Despite combination treatment with liposomal amphotericin B and POS for 39 days, the patient died from pulmonary hemorrhage. This case highlights the need for continued awareness of breakthrough zygomycosis in patients receiving POS.