Erdheim-Chester disease (ECD) is rare non-Langerhans histiocytosis with distinctive radiologic and pathologic entities. We report a rare case of which ECD was involving the breast with only eight similar cases reported in the English literature. Our patient was a 52-year-old female patient with ECD involving the breast, mesentery, left kidney, retroperitoneum and the skeleton. The diagnosis was based on distinctive imaging and histopathological findings. The patient received a new novel treatment as part of a clinical trial in the United States and showed clinical and radiological improvement. SIMILAR CASES PUBLISHED: 8