Neuroendocrine tumors, or NETs, are growths that begin in the specialized cells of the body’s neuroendocrine system. These cells share traits of both nerve cells and hormone-producing endocrine cells and are found throughout the body. When these cells grow abnormally, they form tumors that can be benign or cancerous. Neuroendocrine cancers are considered uncommon, but the number of people diagnosed has been gradually increasing.
Incidence and Prevalence Data
Incidence and prevalence data help explain the rarity of neuroendocrine cancers. Incidence is the number of new cases diagnosed in a year, while prevalence is the total number of people living with the disease at a given time.
In the United States, the incidence rate for NETs is estimated to be around 7 cases per 100,000 people each year, with similar trends in other regions. The prevalence is notably higher, at around 35 cases per 100,000 people. This difference exists because many NETs are slow-growing, allowing individuals to live with the disease for many years.
The rising prevalence figures reflect both an increase in new diagnoses and improved survival. Overall, neuroendocrine neoplasms account for a small fraction of all cancer diagnoses, estimated at less than 2%.
Variations in Rarity by Tumor Type
The term “neuroendocrine cancer” is a broad classification for a diverse group of tumors, and their rarity can differ significantly depending on where they originate. The primary site is a major factor in determining how common a specific type of NET is.
The most frequent locations for neuroendocrine tumors include:
- The gastrointestinal (GI) tract, including the stomach, small intestine, appendix, and rectum. GI NETs are the most common category, with tumors of the small intestine and rectum being diagnosed more often due to screenings like colonoscopies.
- The lungs. These can range from slow-growing typical carcinoid tumors to more aggressive forms.
- The pancreas. These are another significant subgroup, though less common than GI or lung NETs.
- Rarer sites, such as the thyroid gland, adrenal glands, thymus, and even the skin in the form of Merkel cell carcinoma.
Factors Influencing Diagnosis Rates
The observed increase in neuroendocrine cancer diagnoses over the past decades is largely attributed to better medical technology and greater physician awareness. These advancements have enabled the detection of tumors that might have gone unnoticed or been misdiagnosed previously.
Advanced imaging, such as high-resolution CT scans, MRIs, and specialized PET scans, can detect smaller tumors with more accuracy. This has led to an increase in incidental findings, where tumors are discovered during medical procedures for unrelated health issues.
Increased knowledge within the medical community has also improved the diagnostic process. As physicians have become more familiar with the signs of NETs, they are better equipped to order the appropriate tests, which helps overcome diagnostic delays that can occur because the symptoms are often vague.
Contextualizing Rarity and Prognosis
While neuroendocrine cancers are rare, survival outcomes can be favorable, particularly when a tumor is detected at an early stage. The slow-growing nature of many NETs contributes to this outlook. The overall five-year relative survival rate for all NETs combined is approximately 51%, a figure that has steadily improved.
This is a general statistic, and an individual’s prognosis is dependent on several factors. The tumor’s specific location, its grade (how quickly cells are dividing), and its stage (whether it has spread) all influence the outlook.
For example, the five-year survival rate for localized gastrointestinal NETs is over 90%. For lung NETs confined to their original site, the survival rate is also very high. In cases where the cancer has spread to distant parts of the body, the prognosis is less favorable, but many individuals still live for years with metastatic disease.