Cohort of Well-differentiated Grade 3 Neuroendocrine Digestive Tumors

Digestive neuroendocrine tumors are rare tumors and cell differentiation is a major prognostic marker of neuroendocrine tumors.

The 2010 WHO Classification defined three groups of tumor according to the combination of the morphological characteristics and the mitotic index and/or the Ki-67 index: Grade 1 and 2 corresponded to well differentiated neuroendocrine tumors whereas grade 3 corresponded to poorly differentiated lesions entitled neuroendocrine carcinomas (NEC). It was assumed that no well-differentiated neuroendocrine tumor with a mitotic- or a Ki-67- index above 20% existed.

Recently, a proportion of neuroendocrine tumors corresponding to grade 3 neuroendocrine tumors with a proliferation- or Ki-67 index > 20% and with a well-differentiated morphology have been identified. This entity has been partially explored and may have a different survival than grade 3 NEC. Furthermore, targeted therapies, and used in pancreatic neuroendocrine tumors have not been assessed in this case.

The TENpath network is a pathological network whose goal is the systematic reading of all diagnosed cases of neuroendocrine tumors. As part of this network, nearly 3.000 neuroendocrine tumors were reviewed by pathologist experts. Of all the reviewed tumors, 167 were identified as well-differentiated grade 3 neuroendocrine tumors, observed Ki-67(5.6%) confirming the existence of this entity.

Treatment and follow-up of well-differentiated grade 3 tumors are not consensus-based and recommendations are exclusively based on experts' opinions. The purpose of this study is to define the characterization of this entity and evaluate the efficacy of chemotherapy on well-differentiated grade 3 digestive neuroendocrine tumors identified from the TENpath network.