Flow diagram of enrolled patients into 3 final GVHD groupings according to NIH-CC. A proportion of patients in all 3 groups had a history of classical aGVHD before day +100, including 45 of 132 (34.1%) in the control group, 43 of 51 (84.3%) in the cGVHD group, and 48 of 60 (80%) in the L-aGVHD group. Of the 51 pediatric patients with cGVHD (43 meeting NIH-CC), most (84.3%) had progressive/quiescent cGVHD, meaning that their cGVHD developed concurrently with or after a past history of aGVHD. Twenty cGVHD cases (39.2%) had concurrent aGVHD manifestations at the time of cGVHD diagnosis (overlap syndrome), and 8 others (15.7%) had a history of L-aGVHD that had resolved before their quiescent cGVHD diagnosis. De novo cGVHD without a history of aGVHD was rare (15.7%). L-aGVHD cases were further subdivided into persistent L-aGVHD (aGVHD persisting after day +100; n = 29; 48.3%), recurrent L-aGVHD (aGVHD manifestations returning after day +100 following a period of resolution; n = 19; 31.7%), or new-onset de novo L-aGVHD (n = 12; 20%).