Extensive Cutaneous and Scalp Metastases From Hormone Receptor-Positive Breast Cancer Successfully Treated With CDK4/6 Inhibitor Therapy: A Case Report.

Cutaneous metastases from breast cancer (CMBC), including those involving the scalp, are typically observed in advanced stages of the disease and are relatively uncommon, particularly in hormone receptor-positive subtypes. We present the case of a 68-year-old woman with breast cancer metastatic to the skin, characterized by multiple firm, hyperpigmented, painless nodules distributed over the body, including the scalp. The patient has been treated with a CDK4/6 inhibitor (ribociclib) in combination with endocrine therapy (ET) (letrozole) since April 2024. During follow-up, all subcutaneous nodular lesions showed significant regression. By April 2026, skin color had returned to normal in most previously affected areas, and the majority of nodules had resolved. The scalp lesion completely disappeared, with full hair regrowth at the affected site. Treatment of CMBC with CDK4/6 inhibitor-based therapy has been scarcely reported, with most cases describing ET alone. This case highlights the potential role of CDK4/6 inhibitors and documents a notable response in the scalp, skin, and subcutaneous tissue, which has not been widely described.