The purpose of this study is to analyse clinical data of well-differentiated grade 3 digestive neuroendocrine tumors. These rare tumors may have a different disease evolution, response to chemotherapy and prognostic.

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.

Inclusion Criteria:

• Well-differentiated grade 3 neuroendocrine digestive tumors
• Patient of 18 years old and more

Exclusion Criteria:

• Patient opposed to data collection as part of the study
• Digestive neuroendocrine tumors Grade 1-2
• Grade 3 poorly differentiated digestive neuroendocrine tumors
• Malignant disease diagnosed in the last 5 years (except basal cell of the skin and in situ cervical carcinoma)
• Other non-digestive neuroendocrine tumors
• Mixed neuroendocrine non neuroendocrine neoplasm

digestive tumors recorded in the national registry of endocrine tumors (GTE) and the TENpath registry