Case Report: response of HER2-positive ductal carcinoma in situ to osimertinib with supporting in vitro evidence - Takeaways - MDSpire

Case Report: response of HER2-positive ductal carcinoma in situ to osimertinib with supporting in vitro evidence

  • By

  • Shogo Baba

  • Mami Koketsu

  • Hajime Kuroda

  • Megumi Suzuki

  • Hiroshi Nishihara

  • Yasutaka Kato

  • Hiroyuki Kawami

  • Oi Harada

  • May 20, 2026

  • 0 min

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  • 1

    A 74-year-old woman with HER2-positive DCIS and NSCLC showed significant tumor reduction after osimertinib treatment.

  • 2

    Osimertinib, an EGFR inhibitor, demonstrated a marked decrease in Ki-67 from 20-30% to 1% in the patient's DCIS.

  • 3

    In vitro studies confirmed osimertinib's ability to inhibit HER2 phosphorylation and cell proliferation in HER2-positive breast cancer.

  • 4

    The patient's DCIS was initially high-grade, but postoperative examination revealed only a small amount of residual disease.

  • 5

    These findings suggest osimertinib may be a potential treatment option for HER2-positive breast cancer, warranting further research.

Original Source(s)

Case Report: response of HER2-positive ductal carcinoma in situ to osimertinib with supporting in vitro evidence

  • by Shogo Baba, Mami Koketsu, Hajime Kuroda, Megumi Suzuki, Hiroshi Nishihara, Yasutaka Kato, Hiroyuki Kawami, Oi Harada

  • May 20, 2026

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