Development of Focal Nodular Hyperplasia Post Dual Anti-HER2 Blockade with Pertuzumab and Trastuzumab in a Patient with Breast Cancer: A Case Report and Literature Review

Abstract Targeted therapies like trastuzumab and pertuzumab have substantially improved outcomes in HER2-positive breast cancer with rare reports of significant adverse events. One such rarely reported adverse event is focal nodular hyperplasia (FNH), an uncommon hepatic condition, typically benign and asymptomatic, but its development following dual anti-HER2 therapy is not commonly documented. We report the case of a 61-year-old woman with HER2-positive breast cancer highlighting the unusual development of FNH following dual anti-HER2 therapy. Routine follow-up imaging posttreatment revealed the development of hepatic nodules. Imaging confirmed a diagnosis of FNH, with no radiologic evidence of malignancy or metastatic disease. The patient remained asymptomatic, and following hepatology consultation, continuation of treatment was recommended with regular imaging follow-up to monitor hepatic lesions. Although it is benign and asymptomatic, FNH warrants careful monitoring in patients on prolonged targeted therapy. Further research is required to elucidate the mechanisms underlying the association between HER2-targeted therapies and hepatic alterations, which could inform evidence-based strategies for monitoring and management in clinical practice.