Patients with malignancies undergoing chemotherapy are at increased risk for severe infections and systemic complications, especially when associated with multiple comorbidities. We report a case of invasive ductal breast carcinoma complicated by fungal rhinosinusitis caused by Fusarium sp., highlighting diagnostic challenges and fatal outcome. A 75-year-old woman with metastatic invasive ductal breast carcinoma to the liver and bone, receiving neoadjuvant chemotherapy, with hypertension and type 2 diabetes mellitus, was admitted on April 4, 2025, due to general condition deterioration, hypotension, and altered mental status. She had severe hyponatremia, KDIGO stage 3 acute kidney injury, and elevated inflammatory markers. Cranial CT showed frontal and sphenoidal sinus disease with bilateral air-fluid levels. Empirical vancomycin, ceftriaxone, and ampicillin were initiated for suspected bacterial meningoencephalitis. Blood cultures were negative, lumbar puncture was unremarkable, and echocardiography showed no vegetations; vancomycin and ampicillin were discontinued, and ceftriaxone was maintained. Given the suspicion of invasive fungal sinusitis, liposomal amphotericin B was started, and nasal endoscopy was performed, revealing tissue necrosis in the nasal turbinates, septum, tonsillar pillars, palate, vallecula, epiglottis, and tongue base. Surgical debridement and biopsies were performed. The patient developed uncontrollable hemorrhage and refractory shock, dying during the procedure on April 10, 2025. Post-mortem diagnosis revealed numerous hyaline septate branching hyphae on direct mycological examination, with culture growing Fusarium sp. Histopathology showed poorly differentiated carcinoma with immunohistochemistry positive for breast cancer, along with filamentous fungal structures on PAS and Grocott stains. Invasive fusariosis is a severe fungal infection mainly affecting oncohematological patients and is rare in solid tumors. Few cases of Fusarium-related sinus disease have been reported in recognized risk populations. This case illustrates its complexity in the context of progressive malignancy with concomitant fungal disease and reinforces the need for intensive surveillance in cancer patients at risk for opportunistic infections.
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