The Incidence and Clinical Characteristics of Interstitial Lung Disease Associated with CDK4/6 Inhibitors in Breast Cancer Patients: A Retrospective Multicenter Study

<i>Background and Objectives:</i> CDK4/6 inhibitors (CDK4/6i) have revolutionized the treatment of hormone receptor-positive HER2 negative (HR(+)/HER2(-)) breast cancer. Despite their efficacy, interstitial lung disease (ILD) remains a rare but potentially fatal adverse effect. This study aims to evaluate the incidence and clinical characteristics of ILD associated with CDK4/6 inhibitors in breast cancer patients in Turkey. <i>Materials and Methods</i>: A retrospective multicenter analysis included 464 breast cancer patients treated with CDK4/6 inhibitors between January 2017 and April 2024. Patients receiving ribociclib or palbociclib were evaluated for the development of ILD. Radiological assessments were performed to confirm ILD and exclude other conditions. Clinical characteristics, treatment regimens, and outcomes were analyzed. <i>Results</i>: ILD was identified in 10 patients (2.1%). The average age of the affected patients was 62.5 ± 9.85 years. Hypersensitivity pneumonitis and nonspecific interstitial pneumonia (NSIP) were the most common radiological patterns. Palbociclib was implicated in six cases, while ribociclib was associated with four cases. Grade 3 pulmonary toxicity was observed in eight patients, and Grade 4 toxicity in two patients. One patient who was on palbociclib died due to ILD. No significant correlation was found between ILD and age, smoking status, lung metastases, or prior thoracic radiotherapy. <i>Conclusions</i>: The incidence of CDK4/6 inhibitor-associated ILD in Turkish breast cancer patients appears higher than previously reported in clinical trials. More robust, long-term studies are necessary to identify potential risk factors and mitigate ILD-related mortality.