Reassessing a hypermetabolic splenic lesion in breast cancer: PET/CT findings and insights from multimodal imaging and multidisciplinary evaluation

Background [18F]FDG PET/CT is commonly employed for staging and response assessment in breast cancer, yet splenic metastases are exceptionally rare. Hypermetabolic splenic lesions on PET/CT often provoke concern for distant spread but may reflect benign vascular anomalies. Distinguishing treatment-responsive metastases from mimics, such as atypical hemangiomas, poses a diagnostic challenge, particularly when biopsy is impractical. Case presentation A 39-year-old woman with newly diagnosed HER2-positive invasive ductal carcinoma underwent baseline PET/CT, revealing an intensely FDG-avid splenic nodule (SUVmax 6.5). Abdominal MRI demonstrated a 16 mm lesion without diffusion restriction and progressive post-contrast enhancement, suggestive of an atypical hemangioma. She received nine cycles of neoadjuvant carboplatin, docetaxel, pertuzumab, and trastuzumab. Interim PET/CT and MRI after chemotherapy showed complete metabolic resolution of the splenic focus and nodule shrinkage to 5 mm, with preserved benign imaging features. Conclusion Multimodal imaging combined with multidisciplinary consensus can help clarify uncertain [18F]FDG PET/CT findings and avoid unnecessary changes in management when percutaneous biopsy is impractical. However, histopathology remains the definitive diagnostic standard, and the diagnosis in this case is presumptive in the absence of tissue confirmation.