The mammary gland undergoes significant changes throughout a woman's life
from embryonic development to transformations after breastfeeding and during aging. These processes, while essential for normal breast physiology, can increase breast cancer risk when disrupted. This review explores three critical stages: embryonic development
postlactational involution
and age-related lobular involution (ARLI). We highlight key signaling pathways-Wnt, FGF, SHH, Notch, EGFR, and BMP-that guide embryonic development and discuss how their dysregulation can contribute to abnormal growth. For postlactational involution, we examine the two-phase process of cell death and tissue remodeling, showing how disruptions during this period, particularly postpartum, may foster a tumor-promoting environment. We also delve into ARLI and the role of cellular senescence in the aging mammary gland, focusing on the senescence-associated secretory phenotype (SASP) and its impact on inflammation and tissue remodeling. Understanding these processes provides new opportunities for breast cancer prevention and treatment strategies.