{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,8,15]],"date-time":"2026-08-15T18:03:28Z","timestamp":1786817008498,"version":"build-2736575974"},"reference-count":10,"publisher":"Frontiers Media SA","license":[{"start":{"date-parts":[[2026,5,20]],"date-time":"2026-05-20T00:00:00Z","timestamp":1779235200000},"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:p>\n                    Ductal carcinoma\n                    <jats:italic>in situ<\/jats:italic>\n                    (DCIS) carries a risk of progression to invasive ductal carcinoma (IDC), and local treatments such as mastectomy and radiation therapy are commonly used. This case report describes a 74-year-old Japanese woman with concurrent HER2-positive DCIS and non-small cell lung cancer (NSCLC) with EGFR mutation who showed a remarkable response to osimertinib, an epidermal growth factor receptor inhibitor used to treat NSCLC. At initial presentation, the breast lesion measured 28 \u00d7 11 \u00d7 29 mm. Biopsy revealed high-grade DCIS with a HER2-immunohistochemistry score of 3+ and a Ki-67 index of 20\u201330%. The NSCLC was subsequently resected, and adjuvant osimertinib therapy was initiated postoperatively. Two months after treatment initiation, a right mastectomy was performed. Postoperative pathological examination showed a marked reduction in tumor size to 8 \u00d7 3 mm and a marked decrease in Ki-67 to 1%. These findings indicated multiple post-chemotherapy changes, with only a small amount of high-grade DCIS remaining, suggesting a therapeutic effect of the lung cancer treatment. Assessment of the inhibitory effect of osimertinib on HER2\n                    <jats:italic>in vitro<\/jats:italic>\n                    demonstrated that osimertinib inhibited cell proliferation in a HER2 expression-dependent way. Western blotting also suggested the inhibition of HER2 phosphorylation. Therefore, these findings suggest that the remarkable response of HER2-positive DCIS in this case may be attributable to the HER2-inhibitory effect of osimertinib. Further research is warranted to determine whether osimertinib could serve as a potential treatment option for HER2-positive breast cancer, including DCIS.\n                  <\/jats:p>","DOI":"10.3389\/fonc.2026.1845658","type":"journal-article","created":{"date-parts":[[2026,5,20]],"date-time":"2026-05-20T04:46:03Z","timestamp":1779252363000},"update-policy":"https:\/\/doi.org\/10.3389\/crossmark-policy","source":"Crossref","is-referenced-by-count":1,"title":["Case Report: response of HER2-positive ductal carcinoma in situ to osimertinib with supporting in vitro evidence"],"prefix":"10.3389","volume":"16","author":[{"given":"Shogo","family":"Baba","sequence":"first","affiliation":[{"name":"Department of Pathology and Genetics, Laboratory of Cancer Medical Science, Hokuto Hospital","place":["Obihiro, Hokkaido, Japan"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Mami","family":"Koketsu","sequence":"additional","affiliation":[{"name":"Department of Pathology and Genetics, Laboratory of Cancer Medical Science, Hokuto Hospital","place":["Obihiro, Hokkaido, Japan"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Hajime","family":"Kuroda","sequence":"additional","affiliation":[{"name":"Department of Diagnostic Pathology, Adachi Medical Center, Tokyo Women\u2019s Medical University","place":["Adachi, Tokyo, Japan"]},{"name":"Department of Clinical Pathology, Hokuto Hospital","place":["Obihiro, Hokkaido, Japan"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Megumi","family":"Suzuki","sequence":"additional","affiliation":[{"name":"Megumi Breast Clinic","place":["Obihiro, Hokkaido, Japan"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Hiroshi","family":"Nishihara","sequence":"additional","affiliation":[{"name":"Department of Pathology and Genetics, Laboratory of Cancer Medical Science, Hokuto Hospital","place":["Obihiro, Hokkaido, Japan"]},{"name":"Center for Cancer Genomics, Keio University School of Medicine","place":["Shinjuku, Tokyo, Japan"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Yasutaka","family":"Kato","sequence":"additional","affiliation":[{"name":"Department of Pathology and Genetics, Laboratory of Cancer Medical Science, Hokuto Hospital","place":["Obihiro, Hokkaido, Japan"]},{"name":"Center for Cancer Genomics, Keio University School of Medicine","place":["Shinjuku, Tokyo, Japan"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Hiroyuki","family":"Kawami","sequence":"additional","affiliation":[{"name":"Department of Pathology and Genetics, Laboratory of Cancer Medical Science, Hokuto Hospital","place":["Obihiro, Hokkaido, Japan"]},{"name":"Center for Breast Diseases and Breast Cancer, Hokuto Hospital","place":["Obihiro, Hokkaido, Japan"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Oi","family":"Harada","sequence":"additional","affiliation":[{"name":"Department of Clinical Pathology, Hokuto Hospital","place":["Obihiro, Hokkaido, Japan"]},{"name":"Department of Clinical Pathology, Kameda Medical Center Laboratory","place":["Kamogawa, Chiba, Japan"]}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"1965","published-online":{"date-parts":[[2026,5,20]]},"reference":[{"key":"B1","doi-asserted-by":"publisher","DOI":"10.3322\/caac.21321","article-title":"Cancer statistics: breast cancer in situ","volume":"65","author":"Ward","year":"2015","journal-title":"CA Cancer J Clin"},{"key":"B2","doi-asserted-by":"publisher","DOI":"10.1038\/s41416-019-0478-6","article-title":"Ductal carcinoma in situ: to treat or not to treat, that is the question","volume":"121","author":"van Seijen","year":"2019","journal-title":"Br J Cancer"},{"key":"B3","doi-asserted-by":"publisher","DOI":"10.1016\/S0140-6736(24)00425-2","article-title":"Ductal carcinoma in situ of the breast: finding the balance between overtreatment and 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lung cancer with osimertinib","volume":"24","author":"Liu","year":"2018","journal-title":"Clin Cancer Res"}],"container-title":["Frontiers in Oncology"],"original-title":[],"link":[{"URL":"https:\/\/www.frontiersin.org\/articles\/10.3389\/fonc.2026.1845658\/full","content-type":"unspecified","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2026,5,20]],"date-time":"2026-05-20T04:46:29Z","timestamp":1779252389000},"score":1,"resource":{"primary":{"URL":"https:\/\/www.frontiersin.org\/articles\/10.3389\/fonc.2026.1845658\/full"}},"subtitle":[],"short-title":[],"issued":{"date-parts":[[2026,5,20]]},"references-count":10,"alternative-id":["10.3389\/fonc.2026.1845658"],"URL":"https:\/\/doi.org\/10.3389\/fonc.2026.1845658","relation":{},"ISSN":["2234-943X"],"issn-type":[{"value":"2234-943X","type":"electronic"}],"subject":[],"published":{"date-parts":[[2026,5,20]]},"article-number":"1845658"}}