TP53 and bronchiolitis obliterans syndrome: Kastelein et al. analyzed p53 expression (classified as normal, overexpressed or loss of expression) of formalin-fixed paraffin-embedded biopsies (FFPE) from 635 BO patients consisting of n = 586 non-progressors (those who did not develop HGD/OAC from baseline BO/LGD) and n = 49 progressors (those who went on to develop HGD/OAC from baseline BO/LGD) via IHC with consensus between two pathologists required [19].