Lack of efficacy of Intrapleural applications of Trastuzumab for local Control in metastatic HER-2-positive Breast Cancer

While systemic treatment for HER-2-positive breast cancer is well established, strategies for local progression, particularly pleural infiltration, are less clearly defined. In this case, a 52-year-old female patient with HER-2-positive, hormone receptor-negative breast carcinoma and bilateral pleural effusions was initially treated systemically with docetaxel, trastuzumab, and pertuzumab, followed by a switch to trastuzumab deruxtecan (T-DXd) upon systemic progression. When a unilateral pleural effusion developed, an attempt was made to control the local progression through intrapleural administration of trastuzumab. Despite four doses, the effusion size remained unchanged, indicating insufficient local disease control. Subsequently, thoracic surgical intervention with pleurectomy and pleurodesis was performed. Histopathology confirmed HER-2-positive tumor cells in the pleura. The progression of the effusion led to an adjustment of systemic therapy to tucatinib, capecitabine, and trastuzumab. This case demonstrates that intrapleural administration of trastuzumab did not achieve adequate local control of pleural infiltration in HER-2-positive breast cancer.