Beyond the Tumor: Invasive Fungal Infection Unveiled in HER2-Positive Breast Cancer Patient Mimicking Disease Relapse.

Introduction: Breast cancer is a major global health concern among all malignancies, with HER2-positive breast cancer representing a particularly aggressive subtype. It affects approximately 20% of patients and is associated with a high risk of relapse. The management of HER2-positive breast cancer has been significantly improved by targeted therapies, though challenges remain, especially in resource-limited settings. Invasive fungal infections are also common and can manifest as metastatic lesions in immunocompromised cancer patients undergoing intensive treatments making the diagnosis challenging for the oncologists. Case Description: We report a case of a 39-year-old premenopausal female with relapsed HER2-positive breast cancer complicated by an invasive fungal infection. The patient initially presented with a 5 × 5 cm right breast lump, which was diagnosed as invasive ductal carcinoma, HER2-positive estrogen and progesterone receptor negative. Despite receiving chemotherapy with doxorubicin, cyclophosphamide, paclitaxel in the neoadjuvant setting and breast conservation surgery, the patient experienced disease recurrence. She was then treated with modified radical mastectomy followed by adjuvant chemotherapy TCH (trastuzumab, carboplatin, and docetaxel) six cycles. After three cycles, she developed high-grade fevers, renal impairment, and altered mental status. Imaging initially suggested ongoing infective vs metastatic process in bilateral renal and CNS parenchyma, so biopsy was performed from brain that revealed Aspergillus flavus infection. Treatment was adjusted to include antifungal therapy with voriconazole, and the patient's condition improved. Practical Implications: This case underscores the critical need for biopsy of new or evolving lesions in cancer patients, particularly when imaging is not convincing enough for a relapse. Accurate diagnosis is essential to differentiate between disease progression and complications such as opportunistic infections. The occurrence of a fungal brain abscess in this patient highlights the importance of considering such invasive opportunistic infections in immunocompromised individuals, especially those undergoing intensive chemotherapy. Furthermore, the challenges faced due to the unavailability of targeted therapies in resource-limited settings emphasize the need for better access to advanced treatments and comprehensive management strategies. This case also calls for heightened vigilance and prompt diagnostic evaluation to address both cancer progression and potential opportunistic infections effectively.