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

By coupling the results from these two different approaches we show that both biopsy size and non-neoplastic component must be taken into account for biopsy adequacy. In particular, we can speculate that if the minimum biopsy area, necessary to confidently (80% concordance) grade gastro-entero-pancreatic neuroendocrine tumors on virtual biopsies ranges between 15 and 30 mm2, and if real biopsies are on average composed of only 80% of neoplastic tissue, then biopsies with a surface area not <12 mm2 should be performed; using 18G needles, this corresponds to a minimum total length of 15 mm.