{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,3,24]],"date-time":"2026-03-24T01:09:24Z","timestamp":1774314564195,"version":"3.50.1"},"reference-count":21,"publisher":"Frontiers Media SA","license":[{"start":{"date-parts":[[2025,12,18]],"date-time":"2025-12-18T00:00:00Z","timestamp":1766016000000},"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>Trastuzumab deruxtecan (T-DXd or DS-8201) is a novel antibody\u2013drug conjugate (ADC) targeting HER2 that has shown significant efficacy in advanced breast cancer. However, data on its use in elderly patients with hormone receptor\u2013positive (HR+)\/HER2-low disease complicated by malignant pleural effusion are scarce. We report the case of a 75-year-old woman with HR+\/HER2-low (HER2 2+\/FISH\u2013 at diagnosis, HER2\u20130 at recurrence) advanced breast cancer who developed multiple lymph node metastases and a large pleural effusion after progression on endocrine therapy plus a CDK4\/6 inhibitor. She received trastuzumab deruxtecan as salvage therapy, initially at a reduced dose of 4.4 mg\/kg because of frailty, followed by escalation to the standard 5.4 mg\/kg dose after good tolerability. Several cycles were administered at extended intervals due to financial constraints. T-DXd therapy resulted in near-complete resolution of the pleural effusion, marked shrinkage of nodal disease, improvement of upper limb edema and respiratory symptoms, and sustained declines in serum tumor markers. Progression-free survival on T-DXd reached 16 months, while overall survival from T-DXd initiation was 18 months. Treatment-related adverse events were limited to mild myelosuppression and gastrointestinal discomfort, without interstitial lung disease. This case suggests that dose-adjusted T-DXd can achieve durable disease control with acceptable safety in a frail elderly patient with HR+\/HER2-low breast cancer and pleural effusion, adding to the growing real-world evidence supporting the use of HER2-directed ADCs beyond traditional HER2-positive populations.<\/jats:p>","DOI":"10.3389\/fonc.2025.1728983","type":"journal-article","created":{"date-parts":[[2025,12,18]],"date-time":"2025-12-18T06:45:37Z","timestamp":1766040337000},"update-policy":"https:\/\/doi.org\/10.3389\/crossmark-policy","source":"Crossref","is-referenced-by-count":1,"title":["Trastuzumab deruxtecan in an elderly patient with HR+\/HER2-low breast cancer complicated by pleural effusion: a case report and literature 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