Abstract Introduction CDK 4/6 inhibitors are an effective and widely used therapy for hormone receptor-positive metastatic breast cancer and have shown significant survival benefit. However, they have been associated with interstitial lung disease and drug-induced pneumonitis, with an estimated incidence of 3.3%(1). Most cases respond favorably to corticosteroid therapy, yet steroid-refractory presentations remain rare and are associated with significant morbidity. Concurrent malignant pleural effusions are uncommon and further compromise respiratory status, creating major therapeutic challenges. This case highlights a presentation of abemaciclib-induced pneumonitis unresponsive to steroids, complicated by persistent loculated malignant pleural effusions. Case Presentation 66-year-old female with stage IV metastatic breast cancer, hypertension, type 2 diabetes, and chronic malignant pleural effusions who presented with progressive dyspnea requiring 3L supplemental oxygen via nasal cannula. She had previously undergone multiple pigtail catheters and pleurX drains placement, which provided transient relief before clogging from extensive debris and loculations. Imaging on admission revealed bilateral multifocal ground-glass opacities and large, loculated pleural effusions. Multidisciplinary evaluation involving pulmonology, interventional radiology, and cardiothoracic surgery determined that she was a poor candidate for pleurodesis or additional drainage, given the low likelihood of meaningful lung re-expansion and prior failed drainages. Bronchoscopy with bronchoalveolar lavage was negative for infection. Findings were consistent with abemaciclib-induced pneumonitis, prompting discontinuation of the drug and transition to fulvestrant for ongoing chemotherapy. Despite high-dose steroid therapy with taper and supportive care, the patient’s dyspnea persisted, and she remained oxygen dependent during hospitalization and at home. Discussion While corticosteroids remain the cornerstone of treatment for drug-induced pneumonitis, a subset of patients demonstrate refractory response, requiring consideration of alternative immunosuppressive agents(2). Concurrently, loculated or nonexpandable malignant effusions often limit standard interventions such as pleurodesis or indwelling catheter placement(3). Early recognition and timely escalation of both oncologic and pulmonary therapies are essential to reduce adverse events associated with lung pathologies mentioned. Current ATS and CHEST guidelines offer limited guidance for managing overlapping pulmonary toxicity and recurrent malignant effusions, highlighting the need for individualized, multidisciplinary care and further research to establish evidence-based strategies. 1. Ghorpade R, et al. A Fatal Case of Abemaciclib-Induced Pulmonary Toxicity. Chest. 2023;164(4):A2183-A2184. 2. Skeoch S, et al. Drug-Induced Interstitial Lung Disease: A Systematic Review. J Clin Med. 2018;7(10):356. 3. Feller-Kopman DJ, et al. Management of Malignant Pleural Effusions: An Official ATS/STS/STR Clinical Practice Guideline. Am J Respir Crit Care Med. 2018;198(7):839-849. This abstract is funded by: none
Solano et al. (Fri,) studied this question.