A positive correlation between IL-1β expression and osteoprotegerin (OPG) was also found, revealing a potential role for OPG in the invasion-promoting effects of IL-1β and showing that IL-1β led to an increase in OPG production, via the p38 and p42/22 mitogen-activated protein kinase (MAPK) signaling pathway, independent of breast cancer cell subtype [18,19]. This evidence concerns the gene TNFRSF11B and breast cancer.