Case Report: Trastuzumab-deruxtecan as 11th line therapy in a metastasized ovarian clear cell carcinoma patient expressing HER2 1+

Ovarian clear cell carcinoma (OCCC) is a rare histologic subtype of epithelial ovarian cancer, accounting for approximately 5%–10% of cases in Western populations. Compared with high-grade serous ovarian cancer, OCCC is characterized by lower sensitivity to conventional cytotoxic chemotherapy and consequently poor outcomes. Given the limited efficacy of standard systemic therapies, there is a considerable unmet need for novel treatment strategies in OCCC. Antibody–drug conjugates (ADCs) have emerged as a promising therapeutic class across several solid tumors. Among these agents, trastuzumab deruxtecan (TDXd) has demonstrated substantial clinical activity in HER2-expressing malignancies and has recently shown efficacy across multiple tumor types in the DESTINY-PanTumor02 trial, but with low evidence in OCCC. Here, we report a patient with heavily pretreated recurrent ovarian clear cell carcinoma who achieved a durable and clinically meaningful response to trastuzumab deruxtecan despite low HER2 expression (IHC 1+).