CDKN2A and idiopathic pulmonary fibrosis: Fibroblast senescence in fibroblastic foci is correlated to poor outcomes in IPF [50], but the variable expression or lack of expression of p16ink4a in the fibroblastic foci of all IPF patients may suggest that senescence of AECs precedes fibroblast senescence, as AEC senescence has consistently been observed in IPF cells and tissues by our group and others (Figure 1) [14–16, 28].