Rare Case of a Patient With Erdheim-Chester Disease Presenting With Atypical Breast Involvement.

Erdheim-Chester disease (ECD) is a rare multisystem disorder characterized by mitogen-activated protein kinase (MAPK) pathway mutations. Herein, we present a unique case of ECD in a 79-year-old female with predominant breast nodules. Comprehensive imaging and histopathological evaluations confirmed the diagnosis. Mammography and ultrasonography revealed multiple hyperdense circumscribed nodules with coalescing masses and blurred margins. Core biopsy revealed infiltrating foamy cluster of differentiation (CD) 68+ and CD1a+ histiocytes. Because the tumor was negative for the BRAF V600E mutation, treatment with interferon-α was initiated. This case highlights the diagnostic challenges associated with ECD, the rarity of breast involvement, and the importance of considering ECD in the differential diagnosis of atypical breast lesions. Comprehensive imaging, histopathology, and genetic testing are essential for accurate diagnosis and treatment decision-making in ECD. Further research and awareness are required to improve recognition and management of this rare disease.