Tubular carcinoma and low-grade hormone receptor-positive breast cancer as candidates for treatment de-escalation

Hormone receptor (HR)-positive/HER2-negative breast cancers encompass a broad biologic spectrum. Low-grade tumors, especially grade 1 luminal cancers and special histotypes such as tubular carcinoma, occupy the indolent end, reflecting morphology, lineage fidelity, genomic simplicity, and limited plasticity. This review frames low-grade HR-positive breast cancer as a distinct setting for de-escalation, highlighting multigene assays’ contribution and limits, late relapse, and the challenge of matching favorable morphology with favorable biology.