Prognostic Significance of Progesterone Receptor Expression in Estrogen-Receptor Positive, HER2-Negative, Node-Negative Invasive Breast Cancer With a Low Ki-67 Labeling Index

PR expression and tumor size were independent prognostic factors in the LA-like subtype, and the LA/PR− subtype had the higher risk of recurrence, especially late recurrence, than the LA/PR+ subtype. In LA-like breast cancers, stratification of prognosis according to PR expression and tumor size is important.