A Case Requiring Differential Diagnosis of Synovitis, Acne, Pustulosis, Hyperostosis, Osteomyelitis Syndrome in the Evaluation of Bone Lesions in Early Breast Cancer

INTRODUCTION: Synovitis, Acne, Pustulosis, Hyperostosis, Osteomyelitis (SAPHO) syndrome is a rare disorder characterized by bone lesions that primarily affect the anterior thoracic wall. These lesions can be difficult to differentiate from bone metastases of malignant tumors. Reports of SAPHO syndrome complicating breast cancer are scarce, necessitating careful diagnostic consideration. CASE PRESENTATION: An 81-year-old woman with a past history of palmoplantar pustulosis presented with of a mass in her right breast. After a biopsy and diagnosis of mucinous carcinoma of the right breast, CT and bone scintigraphy were performed to check for distant metastases. This screening revealed multiple sclerotic bone lesions and abnormal radiotracer uptake, including a bull's head sign at the sternoclavicular joint, a feature distinguishing it from breast cancer bone metastases. Considering her history of skin lesions, clinical course, and characteristic imaging findings, a multidisciplinary team concluded that these bone lesions were not distant metastases but due to SAPHO syndrome. After partial mastectomy of the right breast and sentinel lymph node biopsy, the patient underwent adjuvant therapy with no recurrence at 16 months post-procedure. CONCLUSIONS: In early-stage breast cancer, particularly mucinous carcinoma, which has a low metastatic risk, multiple bone lesions should not be deemed bone metastases based on imaging findings alone. Integrating clinical information, including prior anterior thoracic lesions and skin symptoms, can reduce invasive testing and unnecessary treatment. This case demonstrates the importance of considering SAPHO syndrome as a key differential diagnosis in the management of breast cancer.