{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,6,30]],"date-time":"2026-06-30T04:46:13Z","timestamp":1782794773161,"version":"3.54.5"},"reference-count":27,"publisher":"Frontiers Media SA","license":[{"start":{"date-parts":[[2026,6,30]],"date-time":"2026-06-30T00:00:00Z","timestamp":1782777600000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"content-domain":{"domain":["frontiersin.org"],"crossmark-restriction":true},"short-container-title":["Front. Oncol."],"abstract":"<jats:sec>\n                    <jats:title>Background<\/jats:title>\n                    <jats:p>Metaplastic breast carcinoma (MBC) is a rare and aggressive malignancy accounting for less than 0.2-1% of all breast cancers. MBC with osteosarcomatous differentiation is extremely rare (0.003%-0.12%) and presents significant diagnostic and therapeutic challenges.<\/jats:p>\n                  <\/jats:sec>\n                  <jats:sec>\n                    <jats:title>Case presentation<\/jats:title>\n                    <jats:p>We report a case of a 65-year-old female with history of breast-conserving surgery for left breast invasive carcinoma in 2021, who presented with a recurrent left breast mass in December 2025. After adjuvant therapy including ACT chemotherapy, radiotherapy and capecitabine, imaging revealed a 4.47 x 3.4 x 2.8\u00a0cm irregular mass with calcifications. Core needle biopsy suggested metaplastic carcinoma. After 4 cycles of TP plus immunotherapy showing stable disease, modified radical mastectomy was performed. Final pathology confirmed MBC with osteosarcomatous differentiation (4.5 x 3 x 3\u00a0cm), triple-negative with SATB2 positivity and Ki-67 70%. Postoperative BRCA1\/2 testing was negative, and adjuvant AC chemotherapy combined with immunotherapy was administered.<\/jats:p>\n                  <\/jats:sec>\n                  <jats:sec>\n                    <jats:title>Conclusion<\/jats:title>\n                    <jats:p>This case highlights the diagnostic challenges and treatment considerations for MBC with osteosarcomatous differentiation. Multimodality treatment including surgery, anthracycline-based chemotherapy, immunotherapy, and radiotherapy may provide optimal outcomes.<\/jats:p>\n                  <\/jats:sec>","DOI":"10.3389\/fonc.2026.1883268","type":"journal-article","created":{"date-parts":[[2026,6,30]],"date-time":"2026-06-30T04:25:07Z","timestamp":1782793507000},"update-policy":"https:\/\/doi.org\/10.3389\/crossmark-policy","source":"Crossref","is-referenced-by-count":0,"title":["Metaplastic breast carcinoma with osteosarcomatous differentiation: a case report"],"prefix":"10.3389","volume":"16","author":[{"given":"Xiang","family":"Zhao","sequence":"first","affiliation":[{"name":"School of Nursing, Qilu Medical University","place":["Zibo, China"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"XiaoYu","family":"Sun","sequence":"additional","affiliation":[{"name":"Department of Pathology, Zibo Central Hospital","place":["Zibo, 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