Abstract
BACKGROUND: Cyclin-dependent kinase 4/6 (CDK 4/6) inhibitors have been a significant breakthrough in the management of hormone receptor-positive, HER2-negative metastatic breast cancer based on the results of several large phase III randomized trials. The most common reported toxicity is myelosuppression due to disease such as leukopenia, neutropenia, and thrombocytopenia. Other toxicities associated with CDK 4/6 inhibitors include mucositis, fatigue, gastrointestinal side effects, hepatic toxicities, and QTc prolongation. Despite a good toxicity profile in pivotal studies, the increased rates of use in clinical practice may show less prevalent but lethal toxicity such as lung injury. CASE PRESENTATION: Here, we describe a female patient with metastatic hormone receptor-positive/human epidermal growth factor 2-negative breast cancer who developed lung toxicity while on ribociclib. DISCUSSION: Lung injury is a possible side effect of CDK 4/6 inhibitors and there is an increasing need to understand the management of this side effect.