What Is a Functional vs Non-Functional Endocrine Tumor?
At a Glance
Endocrine tumors are classified as functional if they overproduce hormones causing full-body symptoms, or non-functional if they do not release excess hormones and remain silent. This crucial distinction determines how your tumor is diagnosed and whether you need medication or surgery.
In this answer
3 sections
When you hear the word “tumor,” your first question is often, “Is it cancer?” But when dealing with the endocrine system—which includes organs like the pancreas, pituitary, and adrenal glands—one of the most important initial questions your medical team will ask is whether the tumor is “functional” or “non-functional” [1][2].
Both functional and non-functional tumors can be benign (non-cancerous) or malignant (cancerous). The functional distinction instead comes down to whether the tumor is actively releasing excess hormones into your bloodstream. A functional tumor overproduces hormones, leading to noticeable, full-body symptoms. A non-functional tumor does not release excess hormones and typically only causes symptoms if it grows large enough to physically press against nearby organs [3][4].
Functional Tumors: When Hormones Go into Overdrive
The endocrine system is a network of glands that produce hormones—chemical messengers that control everything from your heart rate to your metabolism. When an endocrine tumor is functional, it acts like a rogue factory, uncontrollably manufacturing and releasing these hormones [5].
Because hormones travel through the bloodstream, a functional tumor in one part of the body can cause symptoms everywhere. These symptoms vary widely depending on exactly which hormone the tumor is producing and which gland is affected. Common signs of hormonal excess include:
- Flushing (sudden warmth and redness in the face or chest) and chronic diarrhea, often seen in a condition called carcinoid syndrome (commonly arising from tumors in the gut or lungs) [2][6].
- Rapid heart rate (palpitations), anxiety, and high blood pressure, which can happen if an adrenal gland tumor produces adrenaline-like hormones (such as in a pheochromocytoma) [7][8].
- Unexplained weight gain, muscle weakness, and easy bruising, which can be caused by excess cortisol (Cushing syndrome, often related to the adrenal or pituitary glands) [9][10].
- Severe drops in blood sugar (hypoglycemia), causing confusion, shakiness, or fainting, seen with pancreatic tumors that overproduce insulin (insulinomas) [2][11].
Because these symptoms are systemic (affecting the whole body) and can be quite severe, functional tumors are often diagnosed earlier in their development before they have grown very large [4][12].
Non-Functional Tumors: The Silent Growers
In contrast, a non-functional endocrine tumor is made up of cells that do not release excess hormones into the bloodstream [3]. Because they don’t pump these chemicals into your system, these tumors are often completely “silent” in their early stages [7].
Non-functional tumors are frequently discovered by accident when you are having a scan (like an ultrasound or CT scan) for an unrelated health issue [4][13]. Doctors sometimes refer to these accidentally discovered growths as incidentalomas.
When non-functional tumors do cause symptoms, it is almost always due to what doctors call a mass effect—meaning the tumor has grown large enough to physically press on surrounding nerves, blood vessels, or organs [5][14]. Depending on where the tumor is located, mass effect symptoms might include:
- Pain in the abdomen or back if a tumor is pressing on surrounding tissues or nerves [4].
- Jaundice (yellowing of the eyes and skin) or digestive issues if a tumor blocks bile ducts in or near the pancreas [15][16].
- Visual changes or headaches if a tumor in the pituitary gland presses against the optic nerves [11][17].
How the Type Impacts Your Care
Whether your tumor is functional or non-functional directly affects the next steps in your medical care.
To determine the type of tumor you have, your doctor will likely use a combination of tools. Functional tumors are confirmed using specialized blood and urine tests that measure your hormone levels [8][2]. Non-functional tumors rely heavily on imaging scans to measure the tumor’s size and precisely map its location [2][18].
The distinction also guides your treatment path:
- For functional tumors: Controlling the devastating symptoms of hormone excess is the immediate priority. Doctors will often prescribe specific medications (like hormone blockers or targeted drugs) to stabilize your hormone levels and make you feel better—as well as make any future procedures safer [19][20]. Once your hormone levels are controlled, surgery is frequently a high priority to remove the tumor and resolve the hormonal imbalance entirely.
- For non-functional tumors: Because they don’t cause hormonal symptoms, the decision to operate is usually based primarily on the tumor’s size, its growth rate, and whether it is pressing on critical structures (mass effect) [20][21]. If the tumor is small and not causing issues, your doctor may simply monitor it over time.
Note: In very rare cases, a non-functional tumor can change over time and begin producing hormones, so your care team will continue to monitor you even if your tumor is initially silent [22][7].
Summary: Functional vs. Non-Functional Tumors
| Feature | Functional Tumors | Non-Functional Tumors |
|---|---|---|
| Hormone Release | Releases excess hormones into the bloodstream. | Does not release excess hormones. |
| Common Symptoms | Full-body symptoms like flushing, heart palpitations, or weight changes. | Silent at first; later causes local pain, jaundice, or visual issues (mass effect). |
| How It’s Found | Often investigated due to severe systemic symptoms. | Often found by accident on a scan (incidentaloma) or when it grows large. |
| Primary Testing | Blood and 24-hour urine tests to measure hormone levels. | Imaging scans (CT, MRI) to measure size and check nearby organs. |
| Treatment Focus | Medications to block hormones, followed by surgery to resolve the syndrome. | Observation or surgery, based mostly on the tumor’s size and location. |
Common questions in this guide
What makes an endocrine tumor functional or non-functional?
What are the symptoms of a functional endocrine tumor?
How are non-functional tumors usually found?
How do doctors test if a tumor is functional?
Will I need surgery for a non-functional tumor?
Questions to Ask Your Doctor
Curated prompts to bring to your next appointment.
- 1.Is my tumor considered functional or non-functional based on my bloodwork and scans?
- 2.If it is functional, what specific hormone is it overproducing, and what medications are available to help block its effects before any surgery?
- 3.If it is non-functional, is it currently pressing on any nearby nerves, blood vessels, or organs?
- 4.How often will we monitor this tumor to ensure it hasn't changed its behavior or started producing hormones over time?
- 5.How does the functional or non-functional nature of my tumor influence whether I need surgery right now?
Questions For You
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References
References (22)
- 1
Management of Gastrointestinal Neuroendocrine Tumors.
Wang R, Zheng-Pywell R, Chen HA, et al.
Clinical medicine insights. Endocrinology and diabetes 2019; (12()):1179551419884058 doi:10.1177/1179551419884058.
PMID: 31695546 - 2
Insulinoma presenting as hypoglycemia during lactose tolerance testing: a case report.
Munro V, McDonell LM, Keough V, Siddiqi FS
Journal of medical case reports 2020; (14(1)):96 doi:10.1186/s13256-020-02419-4.
PMID: 32605595 - 3
The clinical presentation of PIT1 positive pituitary neuroendocrine tumor immunonegative for growth hormone, prolactin, and thyroid stimulating hormone with analysis of clinical and immunostaining dissociation.
Hong S, Shinya Y, Trejo-Lopez JA, et al.
Clinical neurology and neurosurgery 2024; (236()):108075 doi:10.1016/j.clineuro.2023.108075.
PMID: 38056042 - 4
Metastatic retroperitoneal tumor from a non-functional neuroendocrine neoplasia of the left ethmoid-nose-orbitary region: Case report and short review of literature.
Cataldi C, Cerasari S, Poillucci G, et al.
International journal of surgery case reports 2020; (66()):169-173 doi:10.1016/j.ijscr.2019.12.001.
PMID: 31862660 - 5
Pancreatic Polypeptide-Secreting Tumour of the Proximal Pancreas (PPoma)-Ultra Rare Pancreatic Tumour: Clinically Malign, Histologically Benign.
Ilić I, Katić V, Randjelović P, et al.
Medicina (Kaunas, Lithuania) 2019; (55(9)) doi:10.3390/medicina55090523.
PMID: 31450729 - 6
Symptom Management for Well-Differentiated Gastroenteropancreatic Neuroendocrine Tumors: ASCO Guideline.
Perez K, Del Rivero J, Kennedy EB, et al.
JCO oncology practice 2025; OP2500133 doi:10.1200/OP-25-00133.
PMID: 40344544 - 7
Case report - Selective internal radiation therapy (SIRT) in a patient with hyperinsulinemic hypoglycemia due to a metastatic insulinoma with late onset of endocrine activity.
Henker R, Lincke T, Hoffmeister A
Zeitschrift fur Gastroenterologie 2022; (60(9)):1332-1334 doi:10.1055/a-1690-8018.
PMID: 35042268 - 8
Pheochromocytoma and paraganglioma-an update on diagnosis, evaluation, and management.
Jain A, Baracco R, Kapur G
Pediatric nephrology (Berlin, Germany) 2020; (35(4)):581-594 doi:10.1007/s00467-018-4181-2.
PMID: 30603807 - 9
Sporadic Medullary Thyroid Carcinoma with Paraneoplastic Cushing Syndrome.
Pivovarova AI, Patrick S, Reddy PJ
Case reports in endocrinology 2019; (2019()):6414921 doi:10.1155/2019/6414921.
PMID: 31885947 - 10
Ectopic ACTH and CRH Co-secreting Tumor Localized by 68Ga-DOTA-TATE PET/CT.
Papadakis GZ, Bagci U, Sadowski SM, et al.
Clinical nuclear medicine 2015; (40(7)):576-8 doi:10.1097/RLU.0000000000000806.
PMID: 26018709 - 11
A contemporary, multiinstitutional analysis of transcription factor lineage in pituitary adenomas: comparative study of neuroimaging, histopathology, and clinical outcomes.
Cheok SK, Ruzevick J, Briggs RG, et al.
Journal of neurosurgery 2025; (143(1)):146-154 doi:10.3171/2024.10.JNS24853.
PMID: 40085941 - 12
Cystic pancreatic neuroendocrine tumors (cPNETs): a systematic review and meta-analysis of case series.
Hurtado-Pardo L, Cienfuegos JA, Ruiz-Canela M, et al.
Revista espanola de enfermedades digestivas 2017; (109(11)):778-787 doi:10.17235/reed.2017.5044/2017.
PMID: 29072081 - 13
A single institution's 21-year experience with surgically resected pancreatic neuroendocrine tumors: an analysis of survival and prognostic factors.
Cienfuegos JA, Rotellar F, Salguero J, et al.
Revista espanola de enfermedades digestivas 2016; (108(11)):689-696 doi:10.17235/reed.2016.4323/2016.
PMID: 27701882 - 14
A primary sphenoclival skull base neuroendocrin tumor: A rare case report and literature review.
Amine KM, Bouzoubaa Y, Oukessou Y, et al.
International journal of surgery case reports 2024; (121()):109750 doi:10.1016/j.ijscr.2024.109750.
PMID: 38943936 - 15
Incidental Diagnosis of MEN1 Syndrome in a Pediatric Patient Presenting With Obstructive Jaundice and Abdominal Pain.
Jones JD, Cengia B, Conway J, Pawa R
ACG case reports journal 2016; (3(3)):193-5 doi:10.14309/crj.2016.47.
PMID: 27144202 - 16
Pancreatic neuroendocrine tumor featuring growth into the main pancreatic duct and tumor thrombus within the splenic vein: a case report.
Miyata T, Takamura H, Kin R, et al.
Journal of surgical case reports 2020; (2020(7)):rjaa155 doi:10.1093/jscr/rjaa155.
PMID: 32699600 - 17
The risk of concurrent malignancies in patients with multiple endocrine neoplasia type 1: insights into clinical characteristics of those with multiple endocrine neoplasia type 1.
Zhao YX, Wang O, Song A, et al.
Journal of endocrinological investigation 2024; (47(8)):1931-1939 doi:10.1007/s40618-023-02288-w.
PMID: 38161202 - 18
Progress in treatment and follow-up of pheochromocytoma.
Zhou Y, Tai Y, Shang J
European journal of surgical oncology : the journal of the European Society of Surgical Oncology and the British Association of Surgical Oncology 2025; (51(8)):110144 doi:10.1016/j.ejso.2025.110144.
PMID: 40373734 - 19
Surgical management of pancreatic neuroendocrine tumors: an introduction.
Hain E, Sindayigaya R, Fawaz J, et al.
Expert review of anticancer therapy 2019; (19(12)):1089-1100 doi:10.1080/14737140.2019.1703677.
PMID: 31825691 - 20
Non-surgical ablative therapies for inoperable benign insulinoma.
Mele C, Brunani A, Damascelli B, et al.
Journal of endocrinological investigation 2018; (41(2)):153-162 doi:10.1007/s40618-017-0738-3.
PMID: 28755102 - 21
Current Concepts in Parathyroid/Thyroid Surgery.
Townsend KL, Ham KM
The Veterinary clinics of North America. Small animal practice 2022; (52(2)):455-471 doi:10.1016/j.cvsm.2021.12.004.
PMID: 35210059 - 22
Non-functioning neuroendocrine pancreatic tumors transforming to malignant insulinomas - four cases and review of the literature.
Juhlin CC, Skoglund S, Juntti-Berggren L, et al.
Neuro endocrinology letters 2019; (40(4)):175-183.
PMID: 32087093
This page explains the differences between functional and non-functional endocrine tumors for educational purposes. Always consult your endocrinologist or oncologist to understand your specific diagnosis and treatment options.
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