What Is High Grade Neuroendocrine Carcinoma?

High grade neuroendocrine carcinoma is a fast-growing cancer that starts in neuroendocrine cells, which are scattered through the body and release hormones in response to nerve signals. Because these cells exist in many organs, the cancer can arise in several places, most often the lungs and digestive tract. Unlike the much more common slow-growing neuroendocrine tumors, this form grows and spreads quickly, so it is treated more like an aggressive cancer than a slow one. Grade is one of the strongest predictors of how the cancer will behave.¹

What High Grade Means on Your Pathology Report

Pathologists grade neuroendocrine cancers by counting dividing cells under the microscope and by using a stain called Ki-67, which marks cells that are dividing.² The share of cells that light up is called the Ki-67 index. Grade 1 means fewer than 3% of cells are dividing, grade 2 means 3% to 20%, and grade 3 means more than 20%.³ When the cell count and the stain point to different grades, the higher one sets the final grade.⁴

Grade 3 covers two different diseases. It used to mean carcinoma, but some grade 3 cancers are well-differentiated, meaning the cells still look fairly normal. These are called grade 3 neuroendocrine tumors, or NETs.⁵ A neuroendocrine carcinoma, by contrast, has poorly differentiated, abnormal-looking cells, a higher share of dividing cells and more genetic damage than a grade 3 tumor.⁶ Telling the two apart can be hard when the share of dividing cells is below 55%.⁷

Phrases like “poorly differentiated” point toward carcinoma. It is worth asking your oncologist whether your diagnosis is NET G3 or NEC (neuroendocrine carcinoma), since treatment differs. A slow tumor can rarely change into a carcinoma-like cancer over time.⁸

The numbers on a report can also be incomplete. A biopsy is a small sample, and cancers are not uniform, so the part sampled may understate how fast the whole tumor is dividing. That is why some reports say the grade is based on the sample provided and may change if a larger piece is removed at surgery. Ask whether your sample was a small needle biopsy or a surgical specimen, since that affects how complete the picture is.

Small Cell and Large Cell Types

Under the microscope, small cell carcinoma has small, round cells, each smaller than three resting white blood cells, with very little surrounding cytoplasm.⁹ Large cell carcinoma has bigger, many-sided cells with more cytoplasm, visible nucleoli and large areas of dead tissue.¹⁰ The two types also carry different protein patterns on special stains, which supports the idea that they are separate diseases.¹¹

Type can affect how treatment goes. Standard chemotherapy shrinks tumors in about 70% of small cell cases versus about 45% of large cell cases.¹²

Reports often abbreviate these as SCNEC and LCNEC. Some reports say “not otherwise specified” when the type isn’t clear. Both types are treated as high grade carcinoma.

The response figures are averages across many people, so a small cell diagnosis does not guarantee a response and a large cell one does not rule it out. Your doctor also weighs where the cancer started, how far it has spread, and your overall health.

Where It Starts and How It Shows Up

The lung is the classic site, but the cancer also arises in the digestive tract and in rarer places like the skin, head and neck, and urinary and reproductive organs.¹³ Among digestive cases, the most common sites are the pancreas (about 19%), large intestine (18%), esophagus (18%) and rectum (16%).¹⁴

Symptoms usually come from the tumor’s size or spread, such as pain, weight loss, cough or jaundice, depending on the site. Some neuroendocrine cancers cause hormone-driven syndromes, such as high calcium or low blood sugar.¹⁵ Nerve-related syndromes, where the immune system attacks nerves, are rare and mostly linked to high grade carcinomas.¹⁶

These cancers can spread before symptoms appear. The liver is a frequent site, and many people are diagnosed at an advanced stage, which shapes treatment.

Some cancers contain both neuroendocrine carcinoma and an ordinary cancer such as adenocarcinoma. These mixed tumors are rare, and the evidence guiding their treatment is limited.

During treatment, some symptoms deserve a prompt call to your team. New yellowing of the skin or eyes can signal a blocked bile duct or liver involvement. A worsening cough, shortness of breath or coughing up blood needs a call, especially with a lung primary. New severe headaches, confusion, weakness or trouble walking should be reported right away, since these cancers can spread to the brain. A fever during chemotherapy is urgent because blood counts may be low.

Risk Factors

A family history of cancer roughly doubles the risk of pancreatic neuroendocrine cancer, and diabetes is linked to almost triple the risk in the pancreas. Smoking and heavy drinking are also linked to higher risk.¹⁷ Neuroendocrine cancers overall have become more common in the US, from about 5 to 8 per 100,000 people between 2000 and 2018, though much of that rise is in slow, low grade tumors found earlier.¹⁸

These figures cover neuroendocrine cancers broadly, not only high grade ones. Most people with these factors never develop the cancer, because smoking, diabetes and family history are common while high grade neuroendocrine carcinoma is rare.

Your diagnosis was not caused by something you did. Many people with this cancer have no identifiable risk factor at all.

Scans and Blood Tests You May Have

An FDG PET scan lights up cells burning lots of sugar, which is typical of fast-growing cancers. A DOTATATE PET scan instead lights up cells carrying the somatostatin receptor, a docking site common on slower neuroendocrine tumors.¹⁹ Most poorly differentiated carcinomas lack that receptor.²⁰ FDG PET is therefore usually more useful for carcinoma, while a positive DOTATATE scan opens the door to certain treatments.

Ask which tracer you’re getting and why. FDG scans usually require fasting beforehand, so follow the preparation instructions you’re given.

Because these cancers spread quickly, staging often includes a CT or MRI of the chest, abdomen and pelvis to see how far disease extends. A brain MRI is commonly added, particularly for lung primaries, since spread there can occur without obvious symptoms. Results decide whether the cancer is considered limited or spread, which shapes whether surgery is possible.

Two common blood markers are chromogranin A and neuron-specific enolase (NSE).²¹ Raised NSE is linked specifically to poorly differentiated cancers.²² In carcinoma, NSE and cytokeratin fragments track with survival.²³ A liquid biopsy, a blood test for tumor DNA, detects carcinoma more readily than slow tumors because these cancers shed more DNA.²⁴ Falling markers during treatment are a good sign, and markers are paired with scans rather than used alone.

Standard Treatment

Nearly all specialists use platinum-etoposide, a combination of a platinum drug with etoposide, as first treatment for carcinoma outside the lung, though the best schedule hasn’t been settled.²⁵ In lung carcinoma, the cisplatin and carboplatin versions work about equally well.²⁶ In one lung group, the cancer stayed controlled about 5 months on average and people lived about 10 months.²⁷

Before the first cycle, your team usually reviews the staging scans and blood tests and checks that your kidneys, liver and blood counts can handle the drugs. Many people have a hearing check, since cisplatin can affect hearing, and are told about nerve effects such as tingling in the fingers. Many centers place a port, a small device under the skin, so drugs can be given without repeated needle sticks.

Standard first chemotherapy is given in cycles, usually every three weeks. Common effects include tiredness, low blood counts and hair loss, and supportive medicines reduce nausea. Scans every few cycles check how the cancer is responding.

Surgery depends on stage. For large cell lung carcinoma, surgery is advised in early stages, combined treatment in stage III, and not in stage IV.²⁸ In colorectal carcinoma that hasn’t spread, about 37% lived 5 years with surgery plus chemotherapy, versus about 16% with chemotherapy alone.²⁹ In pancreatic carcinoma, people who had surgery lived a median 31 months versus 5 months.³⁰ People chosen for surgery are often healthier to begin with, which accounts for some of that gap. If the cancer comes back or keeps growing after standard first chemotherapy, the FOLFIRI regimen shrank tumors in about 3 in 10 people.³¹

Outlook and Survival

In colorectal carcinoma that has spread, only about 6% lived 5 years even with surgery and chemotherapy.³² In lung carcinoma on chemotherapy, about 39% were alive at one year and 11% at two years.³³ Individual outcomes vary with fitness and response.³⁴ Age, overall fitness and response to chemotherapy affect survival,³⁵ and grade and stage are the strongest drivers.³⁶ Primary site matters, because lung, pancreas and colon cancers do not behave identically.

Median survival means half of people lived longer than that figure. The numbers come from people treated years ago, and they can’t predict one person. Ask your team what your own stage and situation mean for you.

Newer Treatments and Clinical Trials

Combining the immunotherapy drugs nivolumab and ipilimumab shrank tumors in about 1 in 5 people with previously treated carcinoma, though average control lasted only about 2 months in that trial.³⁷ Some people respond for much longer.³⁸ Immunotherapy releases the immune system’s brakes on cancer cells, but not every tumor is visible to immune cells. Most people do not respond at all, and researchers are still looking for markers that predict who will benefit, so there is no reliable test yet.

Tarlatamab links immune cells to DLL3, a protein common on these cancers.³⁹ In one reported case, it cleared liver and brain spread.⁴⁰ Another approach, PRRT, delivers radiation through the receptor some neuroendocrine cells carry.⁴¹ For carcinoma, it’s only considered when scans show strong receptor uptake, the share of dividing cells is under 55% and growth isn’t rapid.⁴²

Trials test a new treatment, or a new combination, under a strict plan with regular scans and blood tests. Joining usually involves a screening visit to check that you meet the study’s requirements, such as prior treatments and organ function. You can leave a trial at any time and still receive standard care.

Ask about trials at diagnosis, not only after chemotherapy fails. clinicaltrials.gov lists open studies.

Living With Treatment

Palliative care focuses on comfort and can be given alongside cancer treatment, not only at the end of life.⁴³ About 30% of neuroendocrine cancer survivors report lasting depression symptoms.⁴⁴ Nutrition is often affected, and a Mediterranean diet may ease symptoms.⁴⁵ Ask for a palliative care and dietitian referral early.