TGFB1 and breast cancer: Lastly, our finding that Ltbp1 expression is dramatically elevated during involution, when taken collectively with the fact that LTBP1 appears in two metastatic signatures [5,6] and regulates TGFβ, a factor inducing EMT, suggests that LTBP1 may be a prometastatic element in pregnancy-associated breast cancer (PABC).