CDKN1A and gastrointestinal stromal tumor: In a study of Romero et al., 2009, which analyzed samples from patients with advanced metastasized GIST and which tested 400 mg versus 800 mg imatinib daily [25], proved that tumors had a higher expression of p16 (CDKN2A, 57%) and of p53 (TP53, 47%), whereas expression of p21 (CDKN1A, 27%) and cyclin D1 (CCND1, 8%) was lower.