Incidental Finding of Anterior Abdominal Wall Endometriosis Masquerading as Metastasis on FDG PET/CT in a Breast Cancer Patient

Accurate breast cancer staging using ¹⁸ F FDG PET/CT is crucial, though benign inflammatory conditions can yield false-positive results mimicking metastasis. We present a 44-year-old woman with newly diagnosed invasive ductal carcinoma who underwent a baseline PET/CT. Imaging revealed the primary tumour, axillary node involvement, and an unexpected hypermetabolic nodule in the anterior abdominal wall. Highly suspicious for a metastatic deposit, this finding threatened to inappropriately upstage the patient to Stage IV, which would shift her treatment from curative to palliative intent. An ultrasound-guided core biopsy was performed, and histopathology definitively diagnosed abdominal wall endometriosis, ruling out distant metastasis. This confirmation allowed the patient to safely proceed with a curative-intent mastectomy. This case underscores the necessity of tissue biopsy for isolated hypermetabolic findings to prevent erroneous cancer upstaging.