CDK4 and meningioma: p16 protein levels also showed a significant positive correlation with CDKN2A mRNA expression (Fig. 4d, Pearson R = 0.44, p = 1.9 × 10–6). Also concordant with our mRNA findings, CDK4 protein levels appeared to significantly increase with MG, in a similar manner to p16 (Fig. 5e) and were also significantly higher in WHO grade 2 meningiomas compared to grade 1 (Fig. 5f).