Exceptional Metabolic Response to Ribociclib and Letrozole in a Young Patient With De Novo Multimetastatic Luminal A Pleomorphic Lobular Breast Cancer: A Case Report

Metastatic breast cancer (MBC) with a luminal A profile typically follows an indolent clinical course.However, the pleomorphic lobular subtype can manifest aggressive biology with an atypical dissemination pattern and high tumor burden.We report a case of a 42-year-old female diagnosed with de novo luminal A MBC, characterized by an exuberant multimetastatic state involving multiple visceral organs, serosal surfaces, soft tissues, and the axial and appendicular skeleton.Given this high tumor burden, the patient initiated first-line therapy with the CDK4/6 inhibitor ribociclib in combination with letrozole and goserelin.A near-complete metabolic response was observed across all sites monitored by PET/CT after seven months of treatment.This case highlights the clinical efficacy of combining CDK4/6 inhibitors with endocrine therapy even in scenarios of aggressive, high-volume multimetastatic disease.