When Imaging and Biopsy Mislead: Recurrent Triple-Negative Breast Cancer Mimicking Fat Necrosis.

Triple-negative breast cancer (TNBC) is an aggressive subtype with variable imaging appearances that may mimic benign pathology. Distinguishing recurrence from post-treatment changes such as fat necrosis can be challenging, even with triple assessment. We report a case of a woman in her 40s with a prior history of grade 2 TNBC diagnosed in 2018, treated with neoadjuvant chemotherapy, wide local excision, axillary node clearance, and adjuvant chemoradiotherapy, achieving a complete pathological response. Several years later, a computed tomography (CT) scan performed for peritonitis incidentally identified a lesion beneath the surgical scar. Triple assessment, including clinical examination, imaging, and core biopsy, suggested fat necrosis. However, interval imaging performed for unrelated respiratory symptoms demonstrated a significant increase in lesion size and new sclerotic bone lesions. Repeat assessment revealed metastatic recurrence confirmed on biopsy and PET-CT. This case highlights the limitations of triple assessment in high-risk patients and emphasizes the importance of continued surveillance and a low threshold for re-evaluation in patients with prior TNBC, even when initial findings suggest benign pathology.