Neuroendocrine cancer is classified by the site of origin even if it has spread to another part of the body.  When this occurs, it is referred to as "metastasized".  Although neuroendocrine cancer tumors, which are called NETS, vary in size and how quickly they grow, almost all neuroendocrine cancer is considered malignant, or cancerous.  Some of the commonly-found types of neuroendocrine cancer follows, though this is not an all-inclusive list.

 

Gastrointestinal (GI) NETs

Neuroendocrine cancer most commonly develops in the gastrointestinal tract, which includes the stomach, large intestine, small intestine and appendix.   According to the American Society of Clinical Oncology, the  majority of GI NETs (39 percent) begin in the small intestine, with the rectum (15 percent) as the second most common area, and about 7 percent of GI NETs begin in the appendix, presenting symptoms that may closely mimic appendicitis.

 

Lung NETs

The second most common area for neuroendocrine cancer to develop is in the airways of the lungs. These NETs are less likely to be functional tumors, so they don’t tend to cause symptoms based on hormone production as compared with gastrointestinal NETs. Lung NETs may be central, based in the main airway or airways to the lungs, or peripheral, meaning they develop in the smaller airways toward the outer edges of the lungs.  They may be classified as typical or atypical. This corresponds to the grade, or how different the cancer cells appear compared with normal cells. A typical lung neuroendocrine tumor is low-grade and well-differentiated. It’s the least aggressive form of a lung NET. An atypical lung neuroendocrine tumor is an intermediate-grade tumor, with cells that are less similar to normal cells. Lung NETs also may be classified as small cell neuroendocrine carcinoma, more often called small cell lung cancer. Large cell neuroendocrine carcinoma, a type of non-small cell lung cancer, is another form of lung NET. 

 

Pancreatic NETs

Pancreatic neuroendocrine tumors are more rare than GI or lung NETs. About 7 percent of NETs develop in the pancreas, according to the ASCO. Most pancreatic NETs are nonfunctional and don’t cause symptoms.

 

Functional pancreatic neuroendocrine cancer may be classified into subtypes depending on the specific hormones they produce, though they may overproduce more than one hormone at a time. Subtypes of functional pancreatic NETs include:

• Gastrinoma, which produces too much of the hormone gastrin, possibly leading to overproduction of stomach acid

• Somatostatinoma, which produces a hormone called somatostatin, which may interfere with the production of other necessary hormones such as insulin

• Insulinoma, which makes excess insulin (this type of tumor may cause low blood sugar due to high levels of insulin, but only 10 percent of insulinomas become cancerous)

• Glucagonomas make too much of the hormone glucagon, which may lead to high blood sugar

• VIPomas may produce too much of a hormone called vasoactive intestinal peptide (VIP), possibly causing chronic, watery diarrhea as it moves more water than necessary into the intestines.

 

Neuroendocrine Breast Cancer

Breast cancer is the primary cause of death among Western women and primary neuroendocrine breast cancers (NEBCs) are a rare subtype of breast cancer, accounting for .3% of all neuroendocrine cancers. According to the World Health Organization (WHO), NEBC represents 2–5% of all breast cancer.

 

The symptoms of neuroendocrine breast cancer are similar to those of other types of breast cancer. They may include:

• A lump in the breast or underarm area that is seen as a single or multiple tumors

• Thickening or swelling of part of the breast

• Change in the size or shape of the breast

In addition, neuroendocrine tumors can produce hormones that cause symptoms such as:

• Severe diarrhea

• Severe gastric ulcers

• Uncontrolled blood sugar that responds poorly to treatment

 

Neuroendocrine cancer tumors (NETs) in other parts of the body

Endocrine and nerve cells exist all throughout the body, so NETs can sometimes develop outside of the GI tract, lungs or pancreas.

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