Delayed-Onset Vitiligo in Metastatic HR+/HER2- Breast Cancer During Long-Term Ribociclib Therapy.

Vitiligo is a rare cutaneous adverse event associated with cyclin-dependent kinase 4/6 (CDK4/6) inhibitors. We report a 56-year-old woman with de novo metastatic HR+/HER2- breast cancer who developed vitiligo several years into long-term ribociclib therapy. She was initially treated with palbociclib plus letrozole and later transitioned to a reduced dose of ribociclib due to cytopenias and coverage limitations. After 3 years on ribociclib, she developed asymptomatic hypopigmented patches on her hands and face. Dermatologic evaluation confirmed vitiligo. Treatment was conservative with topical corticosteroids, and ribociclib was continued without interruption. Her metastatic disease remained stable with durable oncologic control. This case highlights delayed-onset vitiligo as an uncommon immune-mediated toxicity during prolonged CDK4/6 inhibitor therapy and demonstrates that such lesions do not necessitate discontinuing effective cancer treatment. LEARNING POINTS: This case highlights that cutaneous autoimmune-like toxicities, while concerning in appearance, do not necessarily warrant discontinuation of an effective anticancer drug if they are mild.Oncologists and dermatologists should be aware of CDK4/6 inhibitor-associated vitiligo, even late in the treatment timeline, and approach it with a collaborative management strategy.Moving forward, further research into the immunological or apoptotic mechanisms of this toxicity may shed light on why it occurs and how best to treat it.