Abstract
BACKGROUND: Palbociclib is a specific inhibitor of cyclin-dependent kinases 4 and 6 that is approved for the treatment of advanced or metastatic breast cancer patients. Despite a good toxicity profile in pivotal trials, where asymptomatic neutropenia was the main adverse effect, its wider use in clinical practice may show less prevalent but serious toxicities. CASE PRESENTATION: Here, we describe a case of pneumonitis due to palbocicblib. A 57-year-old female with breast cancer with bone metastasis presented dyspnea at rest 3 months after beginning treatment with palbociclib and letrozole. Palbociclib-induced pneumonitis was considered the most probable cause after ruling out all alternatives, and the patient was successfully treated with steroids and showed complete remission. CONCLUSIONS: In summary, we present a well-documented case report of pneumonitis related to palbociclib. However, the mechanism of toxicity is still unknown, and there are as yet no reliable biomarkers to predict toxicity with cyclin-dependent kinase 4/6 inhibitors. In this case report, we alert physicians about new drugs that can provoke old toxicities.