Introduction: Non-epithelial primary mammary osteosarcomas are extremely rare. The differentials include metaplastic carcinoma and malignant phyllodes tumour. This is the first published case of primary breast osteosarcoma arising after local radiotherapy. Case Presentation: A 73-year-old female presented with a right-sided breast lump. The same breast had been irradiated 11 years previously for invasive ductal carcinoma. Diagnostic excision revealed a highly cellular, malignant spindle-cell lesion merged with an osteoid matrix and foci of calcification and bone formation. Immunohistochemistry and molecular studies showed no lines of differentiation. Due to the lack of epithelial/glandular differentiation, in situ carcinoma or leaf-like pattern, the diagnosis of post-irradiation osteosarcoma was made. She underwent mastectomy and is disease-free at 8 months of follow-up. Conclusion: Post-irradiation osteosarcoma should be considered in the differential diagnosis of breast lesions showing malignant osteoid. Extensive sampling and careful search for epithelial differentiation is required to guide management. Complete surgical excision is recommended.

中文翻译：

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乳腺放射相关原发性骨肉瘤

简介：非上皮性原发性乳腺骨肉瘤极为罕见。差异包括化生性癌和恶性叶状肿瘤。这是首次发表的局部放疗后出现的原发性乳腺骨肉瘤病例。病例介绍：一名 73 岁女性因右侧乳房肿块就诊。同一个乳房在 11 年前因浸润性导管癌接受过放射治疗。诊断性切除显示高度细胞化的恶性梭形细胞病变与类骨质基质以及钙化和骨形成病灶合并。免疫组织化学和分子研究显示没有分化线。由于缺乏上皮/腺体分化，原位癌或叶状模式，因此诊断为放射后骨肉瘤。她接受了乳房切除术，并且在随访 8 个月时无病。结论：在鉴别诊断为恶性类骨质增生的乳腺病变时，应考虑放疗后骨肉瘤。需要大量取样和仔细寻找上皮分化来指导管理。建议完全手术切除。