Ki67 index higher than 5% has been suggested to be associated with malignancy [61], but due to the overlap of Ki67% values between adenoma and carcinoma and to the observation that in secondary parathyroid hyperplasia and multiglandular parathyroid disease Ki67 index may be higher than in adenoma and carcinoma [59], this marker cannot be used alone [62]. This evidence concerns the gene MKI67 and adenoma.