PS5-06-08: Pseudocirrhosis Following Great Response to CDK4/6 Inhibitor and Endocrine Therapy in a Premenopausal Patient With HR+/HER2- Metastatic Breast Cancer

Abstract Background: CDK4/6 inhibitors revolutionized the treatment of hormone receptor-positive, HER2-negative (HR+/HER2-) metastatic breast cancer (MBC), significantly improving outcomes. In premenopausal patients, their combination with ovarian suppression and endocrine therapy is the standard of care in the first-line. In patients with extensive liver metastases with a great treatment response, rare but clinically relevant complications such as pseudocirrhosis can occur. Recognizing this radiological mimic of cirrhosis is essential to avoid misdiagnosis with disease progression and ensure appropriate management. Methods: We describe a case of pseudocirrhosis in a 43-year-old premenopausal woman with HR+/HER2- MBC and high hepatic tumor burden at diagnosis, who experienced a robust response to first-line treatment. Results: This patient was diagnosed in August 2022 with grade 3 invasive breast carcinoma of no special type, ER 98%, PR 2%, HER2-negative, Ki-67 85%, and extensive liver involvement. Treatment was initiated with tamoxifen plus abemaciclib, transitioning to letrozole following GnRH agonist. Molecular testing revealed no somatic or germline mutations. She experienced radiologic complete response, with only a solitary liver lesion progression in February 2025, which was treated with stereotatic body radiotion therapy. In July 2025, routine labs revealed elevated liver enzymes without clinical symptoms. Laboratory tests showed: ALT 60 (Reference value - RV: 13-35); AST 43 (RV:15-37), GGT 510 (RV