Triple-Negative Inflammatory Metaplastic Breast Cancer Presenting as a Non-Mass Lesion.

Inflammatory breast cancer is exceedingly rare, especially when the pathology involves invasive carcinoma alongside metaplastic carcinoma. This disease constitutes a diagnostic and therapeutic challenge, largely due to a scarcity of documented cases in the literature. We reported a case of a female patient who presented with axillary lymphadenopathy and diffuse swelling of a single breast without a solid mass. During hospitalization, she underwent various diagnostic procedures, including lymph node fine-needle aspiration, axillary lymph node biopsy, pleural effusion puncture, magnetic resonance imaging (MRI), and positron emission tomography-computed tomography (PET-CT). Despite these extensive investigations, a definitive diagnosis could not be established. The pathological nature was ultimately clarified through a core needle biopsy of the breast lesion, which subsequently guided the clinical treatment. This case highlights the complexity and challenge of diagnosing metaplastic carcinoma within inflammatory breast cancer, as well as the necessity of performing a core needle biopsy on inflammatory lesions when no solid mass is present.