CDKN1A and chronic obstructive pulmonary disease: Although induction of p21 was shown to have anti-fibrotic effects in lung fibrosis pathology (Inoshima et al, 2004), other studies have shown that p21-positive senescent cells contribute to the progression of lung fibrosis and chronic obstructive pulmonary disease (COPD) (Liu and Liu, 2020; Schafer et al, 2017).