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Grade 3 well-differentiated neuroendocrine tumours divide fast enough to be called grade 3 yet still look and behave like their slower relatives rather than like neuroendocrine carcinoma. Recognised as separate since 2017, they keep the somatostatin receptor, respond less well to platinum chemotherapy, and in the NETTER-2 trial were among the first treated with lutetium-177 dotatate up front.
Until 2017 every neuroendocrine neoplasm with a Ki-67 above 20 percent was called neuroendocrine carcinoma and treated like small-cell lung cancer. Pathologists noticed that some of these tumours kept the organoid architecture, uniform nuclei and somatostatin receptor expression of well-differentiated tumours, and that their patients lived far longer than those with carcinoma. Multicentre series, notably Heetfeld and colleagues (2015), showed that these tumours, usually pancreatic and usually with a Ki-67 between 20 and 55 percent, responded poorly to platinum-etoposide but survived longer, and the NORDIC NEC series (2013) had already found that a Ki-67 below 55 percent predicted the same pattern. The WHO classified pancreatic NET G3 as a distinct entity in 2017 and extended it to the whole digestive system in 2019; molecularly these tumours carry the MEN1, DAXX and ATRX changes of neuroendocrine tumours and retain p53 and Rb, whereas carcinoma loses them, which is why p53 and Rb immunohistochemistry is now used when morphology is ambiguous.
Treatment evidence is thin because the entity is new and small. Capecitabine with temozolomide is the most used chemotherapy, on the basis of pancreatic tumour data from E2211 and retrospective grade 3 series, and everolimus and sunitinib are used with less evidence. Somatostatin receptor PET is usually positive, often with FDG avidity as well, and this dual pattern makes radioligand therapy plausible: NETTER-2 (Lancet 2024) was designed to include grade 3 tumours with a Ki-67 up to 55 percent alongside higher grade 2 tumours, and first-line lutetium-177 dotatate lengthened progression-free survival from 8.5 to 22.8 months across the 226 patients, the first randomised evidence in this group. COMPOSE randomises well-differentiated aggressive grade 2 and grade 3 gastroenteropancreatic tumours between 177Lu-edotreotide and CAPTEM, everolimus or FOLFOX, and is due to report in 2027.
The practical decisions are about tempo and receptor status. Tumours near the upper end of Ki-67, growing fast or losing receptor expression on PET are treated more like carcinoma with platinum-etoposide, while receptor-positive tumours with slower tempo are treated like grade 2 tumours with radioligand therapy or CAPTEM. Surgery and liver-directed therapy are used as for other well-differentiated tumours when disease is limited. Whether grade 3 tumours should be graded further, and where the Ki-67 line between tumour and carcinoma really lies, remain open.
A small fraction of neuroendocrine neoplasms, most often pancreatic; recognised as a separate entity by the WHO in 2017 for the pancreas and 2019 for the whole digestive system after series showed it outlives neuroendocrine carcinoma and responds less to platinum.
Most pancreatic cancers arise in the head next to the bile duct, which is why jaundice is the presenting sign; bile duct cancers are named by where along the tree they sit.
Same organ: Glucagonoma, VIPoma, Somatostatinoma, Pancreatic ductal adenocarcinoma, Biliary tract cancer (cholangiocarcinoma), Intrahepatic cholangiocarcinoma, Extrahepatic cholangiocarcinoma (perihilar and distal), Biliary tract cancer (all types), Neuroendocrine tumours, Pancreatic neuroendocrine tumours, Extrapulmonary neuroendocrine carcinoma, Gallbladder cancer, Gallbladder adenocarcinoma, Papillary carcinoma of the gallbladder, Mucinous carcinoma of the gallbladder, Adenosquamous and squamous carcinoma of the gallbladder, Neuroendocrine carcinoma of the gallbladder, Incidental gallbladder cancer (found after cholecystectomy), Carcinoma in situ and dysplasia of the gallbladder, Cystic duct carcinoma, Ampullary cancer (ampulla of Vater), Resectable pancreatic ductal adenocarcinoma, Borderline resectable pancreatic ductal adenocarcinoma, Locally advanced unresectable pancreatic ductal adenocarcinoma, Metastatic pancreatic ductal adenocarcinoma, KRAS G12C-mutant pancreatic ductal adenocarcinoma, KRAS wild-type pancreatic ductal adenocarcinoma, BRCA or PALB2-mutant pancreatic ductal adenocarcinoma, Mismatch repair deficient (MSI-high) pancreatic ductal adenocarcinoma, Pancreatic acinar cell carcinoma, Intraductal papillary mucinous neoplasm and other pancreatic cystic precursors, Pancreatoblastoma, Adenosquamous carcinoma of the pancreas, Colloid (mucinous non-cystic) carcinoma of the pancreas, Undifferentiated carcinoma of the pancreas with osteoclast-like giant cells, Invasive carcinoma arising in an intraductal papillary mucinous neoplasm (IPMN-associated carcinoma), Mucinous cystic neoplasm of the pancreas with associated invasive carcinoma (MCN-associated carcinoma), Solid pseudopapillary neoplasm of the pancreas
Morphology, Ki-67 and p53 or Rb immunohistochemistry to separate grade 3 tumour from carcinoma; somatostatin receptor and FDG PET together.
Lutetium-177 dotatate first line for Ki-67 up to 55 percent (NETTER-2); somatostatin analogue alongside.
Capecitabine with temozolomide; everolimus or sunitinib for pancreatic tumours; platinum-etoposide for carcinoma-like tempo or Ki-67 near 55 percent.
COMPOSE: 177Lu-edotreotide against CAPTEM, everolimus or FOLFOX in aggressive grade 2 and grade 3 gastroenteropancreatic tumours.
Resection and liver-directed therapy as for other well-differentiated tumours.
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Patients newly diagnosed with an advanced grade 2 or 3 neuroendocrine tumour of the gut or pancreas that shows somatostatin receptors on imaging can now receive lutetium dotatate as their first treatment, gaining more than a year of additional disease control and a much higher chance of tumour shrinkage. It does not settle whether radioligand therapy is better than other first-line options such as capecitabine-temozolomide or everolimus, and long-term marrow safety with earlier use needs surveillance.
The grade 3 neuroendocrine tumour category, treated differently from neuroendocrine carcinoma, exists because of this framework.
Grade 3 neuroendocrine tumours are treated like aggressive grade 2 tumours (somatostatin analogues, capecitabine-temozolomide, radioligand therapy) rather than with small-cell regimens.
Query for this cancer: (TITLE:"Grade 3 well-differentiated neuroendocrine tumour" OR ABSTRACT:"Grade 3 well-differentiated neuroendocrine tumour" OR TITLE:"NET G3" OR ABSTRACT:"NET G3" OR TITLE:"Grade 3 NET" OR ABSTRACT:"Grade 3 NET" OR TITLE:"Well-differentiated grade 3 neuroendocrine tumour" OR ABSTRACT:"Well-differentiated grade 3 neuroendocrine tumour" OR TITLE:"High-grade well-differentiated NET" OR ABSTRACT:"High-grade well-differentiated NET") AND (treatment OR therapy OR trial OR survival OR diagnosis). Results are unfiltered search hits about Grade 3 well-differentiated neuroendocrine tumour, not a curated reading list.
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Bleeding that does not stop by itself, bleeding from more than one site, or new bruising in several places or one large area.
Sudden severe bone pain, or back pain with weakness or numbness in the legs (possible spinal cord compression).
Sudden severe abdominal pain, a hard or very tender abdomen, or abdominal pain with vomiting and fever. Boxed warning for gastrointestinal perforation on bevacizumab.
Fainting, near-fainting, or an irregular or racing heartbeat; several kinase inhibitors prolong the QT interval and the labels require ECG and electrolyte monitoring.
Avoid grapefruit. Live vaccines are contraindicated.
Avoid grapefruit.
See all on the product pages:177Lu-edotreotideCapecitabine + temozolomide (CAPTEM)EverolimusLutetium-177 dotatatePlatinum + etoposide (EP / CE)Sunitinib·Printable cards in the navigator
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