PS5-06-04: Cdk4/6 inhibitor in extensive cutaneous metastasis breast carcinoma: a case report

Abstract Introduction: Breast cancer is one of the most common malignant tumors affecting women worldwide and Mexico. Cutaneous metastases (CM) occur in 0.7 to 10.4% of all patients diagnosed with cancer although they represent only 2% of all skin tumors. Case report: A 68-year-old female with a positive smoking history. Comorbidities: Chronic obstructive pulmonary disease. Major depressive disorder. History of unspecified right breast cancer, Clinical stage IIB, in 2000, treated with right radical mastectomy and hormonal therapy for 5 years. In 2023, the patient presented with disseminated dermatosis, predominantly on the anterior and posterior thorax and skull, bilateral, characterized by multiple subcutaneous neoplasms measuring 1-3 cm, as well as multiple lymphadenopathy in the cervical and retro auricular regions. In November 2023, an excisional biopsy of a subcutaneous nodule was taken, reporting moderately differentiated infiltrating ductal carcinoma, as well as immunohistochemistry with Estrogen Receptor positive 95%, Progesterone receptor positive 90%, negative HER2, and Ki67 positive in 30%. A Computed Tomography scan of the head-neck-chest-abdomen-pelvis also showed evidence of metastatic disease to the lung, liver, and blastic lesions in the skull, lytic lesions in spine, sacrum, and iliac bones. Examination patient was found with an ECOG score of 2. Her scalp showed multiple subcutaneous nodular lesions with alopecia, multiple cervical and retroauricular lymphadenopathy, and a right mastectomy. She had multiple subcutaneous nodular lesions measuring approximately 1-3 cm, fixed, stony, and painless, in the anterior and posterior regions of the chest. She had bilateral axillary lymphadenopathy, as well as multiple lesions in the abdomen and back. In April 2024, treatment was started with ribociclib 600 mg orally every 24 hours and letrozole 2.5 mg orally every 24 hours plus denosumab. The treatment was well tolerated, with no reported toxicity. During follow-up, all subcutaneous nodular lesions decreased significantly. The lesions were flat and brownish pigmented at that site within the first 3-4 months after treatment. Currently, the skin has returned to normal color at the sites where the lesions were located, and most of the nodules are absent. The scalp has completely disappeared, and hair has reappeared at that site. The latest imaging study (CT scan of the head, chest, abdomen, and pelvis with contrast) reports a partial response with a significant reduction in lesions in the lungs, liver, and bones. Discussion: Extensive CMBC hormone receptor (HR)-positive subtypes are generally present late in the course of the disease and treated with hormonal therapy. CMBC are usually solitary or multiple nodular pinkish lesions (ranging between 1 and 3 cm). The spectrum of presentation of cutaneous metastasis in breast cancer varies in frequency from the common papulonodular variant to much rarer presentations of dermatitis-like metastases. Breast cancer scalp metastases generally present as one or more inflammatory or nodular lesions, telangiectasias, or irregularly shaped skin lesions that are flesh or reddish, making them difficult to identify from other skin carcinomas. The use of aromatase inhibitors (anastrozole and letrozole) in CMBC has been reported; however, treatment with modern CDK4/6 inhibitor-based therapy has not been reported, nor is there any experience with this presentation of the disease. Our case demonstrates that this type of treatment not only acts on visceral and bone disease but also offers adequate penetration at the subcutaneous level, achieving an adequate response in extensive disease. Conclusion: Our case demonstrates that treatment with CDK4/6 inhibitor, achieving an adequate response in CMBC-HR-positive extensive disease and scalp. Citation Format: R. Fernández-Ferreira, V. Bautista-Piña, M. Barragán-Dessavre, G. Cruz-Morales, R. Vicuña-González, R. Anaya Jimenez,, R. Moreno López. Cdk4/6 inhibitor in extensive cutaneous metastasis breast carcinoma: a case report [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 PS5-06-04.