We did not find a general tendency towards a higher Ki67 index in metastases compared to primary tumours, as it was shown by study investigating the Ki67 index in primary breast cancer and corresponding metastases.42 Nevertheless, previously published data for primary ACC tumours15,16 and our analysis of the Ki67 index of the first local recurrence/metachronous metastasis showed that a Ki67 index < 20 might correlate with a slower progression compared to Ki67 ≥ 20. This evidence concerns the gene MKI67 and adrenal cortex carcinoma.