Abstract Introduction: In the treatment of hormonal receptor positive (HR+), HER2 negative (HER2-) metastatic breast cancer (MBC), most guidelines recommend endocrine therapy including CDK4/6 inhibitors as the first-line drug for quality of life. Ribociclib is one of the CDK4/6 inhibitor and has been used with aromatase inhibitors or fulvestrant in HR+, HER2- metastatic breast cancer patient. Various drug reactions related with ribociclib has been reported including skin reaction, liver toxicity and hematologic toxicity. In this study, we aimed to evaluate clinical manifestations and risk factors of dermatologic toxicities in metastatic breast cancer patients who used ribociclib. Method: This study included the patients with metastatic/recurrent breast cancer who were prescribed ribociclib from April 2021 to December 2024 in our single institution. We retrospectively reviewed the medical records of the patients, identified the frequency of recorded skin lesions, the time of occurrence and clinical characteristics of skin reactions. Logistic regression analysis was performed with several clinical factors including BSA (body surface area) and concomitant medications to analyze risk factors related to the occurrence of skin lesions. Results: A total of 110 MBC patients were enrolled during the period. The median was 53 years-old (28-82), 110 patients (100.0%) were female, median BSA was 1.56 m2(range, 1.29∼2.07) and 33 patients (30.0%) showed pre-menopausal status. There were 44 de novo metastatic patients (40.0%) and 66 recurrent patients (60.0%). Ribociclib+letrozole was used in 81 patients (73.6%) and ribociclib+fulvestrant was used in 29 patients (26.4%). Skin toxicity occurred in 29 patients (26.4%), and the median time to skin toxicity onset was 84 days (range, 3-498). Skin toxicity patterns included pruritus, erythematous patches, vitiligo, bullous patches, and desquamation. Grade 1 or 2 skin toxicity occurred in 93.1% of patients, grade 3 skin toxicity occurred in 1 patient and grade 4 toxicity, toxic epidermal necrolysis (TEN), was reported in 1 patient. Dose reduction was done in 7 patients (24.1%) and permanent discontinuation of ribociclib occurred in 1 patient (3.4%). Clinical improvement was achieved in 86.2% of patients with skin reactions following supportive care. Logistic regression analysis results for dermatologic toxicity risk showed that age, ECOG PS, BSA, treatment regimen, hyperlipidemia, and use of statins (HMG-CoA reductase inhibitors) were not risk factors for skin toxicity development. Conclusions: CDK4/6 inhibitors are one of the important treatments for HR+, HER2- MBC. Regardless of clinical efficacy, skin toxicity is a common cause of patient discomfort. Therefore, detailed clinical attention and supportive cares can improve the patient's quality of life. Citation Format: K. Lee, E. Kim, L. Youra, A. Ham, J. Jo, S. Lee, H. Kim, J. Lee, J. Woo, W. Lim, B. Moon, S. Ahn, H. Lee. Analysis of the frequency and associated factors of skin toxicity in patients receiving ribociclib based therapy for metastatic breast cancer abstract. In: Proceedings of the San Antonio Breast Cancer Symposium 2025; 2025 Dec 9-12; San Antonio, TX. Philadelphia (PA): AACR; Clin Cancer Res 2026;32(4 Suppl):Abstract nr PS1-03-16.
Lee et al. (Tue,) studied this question.