Erratum to: KI-67 heterogeneity in well differentiated gastro-entero-pancreatic neuroendocrine tumors: when is biopsy reliable for grade assessment?

Purpose Ki-67 heterogeneity can impact on gastroenteropancreatic neuroendocrine tumor grade assignment, especially when tissue is scarce. This work is aimed at devising adequacy criteria for grade assessment in biopsy specimens.