Abstract
OBJECTIVE: To investigate the clinicopathological characteristics, diagnostic strategies and clinical management of primary low-grade osteosarcoma of the breast occurring after radiotherapy for breast cancer. METHODS: We report a rare case of primary low-grade osteosarcoma of the breast in a 69-year-old female patient with a history of breast cancer radiotherapy, and review the relevant literature to summarize its clinicopathological features, aiming to improve clinicians' and pathologists' recognition and diagnostic capability for this rare disease. RESULTS: The patient was diagnosed with left breast invasive ductal carcinoma (pT2N0M0, Luminal A type) 12 years ago and underwent breast-conserving surgery followed by postoperative radiotherapy and adjuvant chemotherapy. She presented with a recurrent mass at the original radiotherapy site. Following mastectomy and comprehensive pathological evaluation, the final diagnosis was primary low-grade osteosarcoma of the breast. She then underwent a modified radical mastectomy and has been followed up for 22 months with no signs of local recurrence or distant metastasis to date. Primary osteosarcoma of the breast is rare, typically high-grade, and is associated with a poor prognosis and high recurrence rate. Primary low-grade osteosarcoma is exceptionally rare, with only sporadic case reports suggesting a potentially more favorable prognosis compared to its high-grade counterpart. Its bland histological appearance can lead to misdiagnosis or underdiagnosis, and no standardized treatment protocols have been established for this disease. CONCLUSION: Core needle biopsy of radiation-induced low-grade osteosarcoma of the breast is prone to misdiagnosis due to limited sampling and bland histological morphology; comprehensive pathological evaluation of surgical specimens combined with a specific immunohistochemical panel (SATB2, MDM2, β-catenin) is key to a definitive diagnosis. Mastectomy is a reasonable primary treatment option for this rare tumor, and long-term standardized follow-up is necessary. This case report supplements the clinical and pathological data on radiation-induced low-grade osteosarcoma of the breast, and provides a reference for the diagnosis and treatment of this disease.