Quantitative RT-PCR of CDKN2A, CDKN2B, WT1, SFRP1, SFRP2 and SFRP4 mRNA in parathyroid tumors of the validation cohort, showing reduced gene expression of all six selected genes in parathyroid adenomas (n=37) and carcinomas (n=7). Reduction of gene expression was significant versus normal parathyroid (p<0.01). Values represent normalized target gene/GAPDH mRNA ratio.