CD44 and plexiform neurofibroma: In vivo, Riddle et al. studied 28 benign neurofibromas and 16 MPNST human specimens obtained from NF1 patients to test for CD44 and p53 expressions, and the immunoexpression of CD44 was focally positive in all the tested pNF/cNF samples and was particularly upregulated in MPNSTs [85].