Complete Clinical Response in Locally Advanced Metastatic de novo Breast Cancer after Front-Line Treatment with Ribociclib/Letrozole within the RIBANNA Study

Introduction Ribociclib is an orally bioavailable cyclin-dependent kinase 4/6 inhibitor. In combination with aromatase inhibitor letrozole, it has approval for treatment of hormone receptor positive (HR+) and human epidermal growth factor receptor 2-negative (HER2-) advanced breast cancer. First-line therapy with ribociclib + letrozole significantly improves progression-free survival compared to placebo + letrozole in patients with HR+/HER2- advanced breast cancer. In patients with de novo advanced or metastatic breast cancer, ribociclib was able to provide substantial clinical benefit according to data from the MONALEESA-2 study. Case Presentation Here, we report the complete clinical response in a postmenopausal patient with de novo, locally advanced, pulmonary metastatic breast cancer treated with ribociclib + letrozole. Our patient presented an ulcerated breast-consuming tumor with multiple pulmonary metastases. HR+/HER2- breast cancer was confirmed by tumor biopsy. Ki67 expression was 90%. After three months of initial treatment, the tumor-associated ulcerations disappeared, and no measurable pulmonary disease was detectable on CT scan. Treatment was well tolerated, and after dosage reduction due to neutropenia, no further side effects have been documented. At present, complete clinical response remains after 15 months of ongoing treatment. Conclusion This case report documents an exceptional tumor response of a fast growing, locally advanced, pulmonary metastatic HR+/HER2- de novo breast cancer treated by ribociclib/letrozole combination therapy. Treatment success was long lasting with few side effects. The patient was very satisfied with the treatment and had no specific restrictions in her daily life.