Ribociclib-Induced Vitiligo: A Case Report with Histological, Dermatoscopic, Confocal Microscopy, and LC-OCT Findings Along with a Narrative Literature Review

Introduction: CDK4/6 inhibitors have revolutionized the therapeutic management of metastatic estrogen receptor-positive (ER+), HER2-negative breast cancer (BC) by increasing treatment efficacy while maintaining a favorable safety profile. An exceedingly rare adverse event associated with these agents is the development of vitiligo-like skin depigmentation. Objectives: This study aimed to characterize a case of ribociclib-induced vitiligo and investigate its underlying pathogenic mechanisms, with particular focus on vitiligo onset. We report the case of a 60-year-old postmenopausal female with metastatic, hormone-sensitive BC who experienced a durable partial remission during treatment with ribociclib in combination with aromatase inhibitors. During therapy, the patient developed hypopigmented lesions on her upper limbs 34 months after initiation of ribociclib, preceded by pruritus and erythema. Methods: Reflectance confocal microscopy (RCM) optical coherence tomography (OCT), and histopathological examination were used. Result: RCM and OCT proved valuable for real-time assessment and monitoring of skin changes, thereby informing clinical decisions regarding the management of skin toxicity. The presence of an inflammatory infiltrate, comprising lymphocytes and hyper-reflective inflammatory cells, suggests that inhibition of the CDK4/6 pathway may enhance antitumor activity beyond cell cycle arrest by modulating the immune response and promoting immune-mediated tumor control. Conclusions: The observed alterations in melanocyte regression could represent evidence of systemic immune activation and autoimmunity influencing melanocyte viability. These mechanisms may have significant implications for improving patient prognosis.