Typical Carcinoid Tumour of the Lung: Understanding Your Pathology Report

by Katherina Baranova MD and Matt Cecchini MD FRCPC
April 29, 2026

A typical carcinoid tumor of the lung is a slow-growing, low-grade cancer that develops from neuroendocrine cells — specialized cells found in small numbers throughout the walls of the airways that normally produce hormones and chemical signals to help regulate breathing. Typical carcinoid tumors are classified as well-differentiated neuroendocrine tumors, Grade 1 — the least aggressive category in the lung neuroendocrine tumor family. Although typical carcinoid tumors are capable of spreading to lymph nodes and, rarely, to distant organs, the great majority are cured by surgical removal. This article will help you understand the findings in your pathology report — what each term means and why it matters for your care.

What causes typical carcinoid tumor of the lung?

Unlike most other lung cancers, typical carcinoid tumor is not strongly associated with tobacco smoking. The majority of cases are sporadic — meaning they arise without a clear identifiable cause. Typical carcinoid tumors develop when neuroendocrine cells in the airway lining acquire genetic changes that cause them to grow abnormally, but what triggers these changes in most people is not known.

A recognized cause in a minority of patients is an inherited condition called Multiple Endocrine Neoplasia Type 1 (MEN1). MEN1 is caused by an inherited mutation in the MEN1 gene and predisposes affected individuals to tumors of several hormone-producing glands, including the parathyroid glands, the pituitary gland, and the pancreas. Lung carcinoid tumors occur in approximately 5–10% of people with MEN1 and may be multiple. If you have a personal or family history of MEN1-associated tumors, your doctor may recommend referral to a genetic counselor to discuss hereditary risk and genetic testing.

What are the symptoms of typical carcinoid tumor of the lung?

Symptoms depend on the size and location of the tumor. Typical carcinoid tumors are most often found in the central airways — the larger bronchi that lead into the lungs — though some arise in the smaller peripheral airways near the outer edges of the lung.

Tumors in the central airways may cause:

• A persistent cough.
• Coughing up blood-tinged mucus.
• Shortness of breath or wheezing caused by partial blockage of an airway.
• Recurrent or slow-to-resolve pneumonia in the same area of the lung, which can occur when a tumor partially blocks an airway and prevents normal mucus clearance.

Tumors arising in the peripheral airways are often small and may cause no symptoms. These are frequently discovered incidentally — found by chance on a chest CT scan performed for an unrelated reason.

Because typical carcinoid tumors are made up of neuroendocrine cells, they can sometimes release hormones — most commonly serotonin — into the bloodstream. If enough serotonin reaches the general circulation, it can cause a constellation of symptoms called carcinoid syndrome, which includes episodes of skin flushing (sudden redness of the face and neck), diarrhea, and occasionally wheezing. In lung carcinoid tumors, carcinoid syndrome is uncommon and almost always indicates that the tumor has spread to the liver, because the liver normally breaks down serotonin before it can accumulate in the bloodstream. In rare cases, lung carcinoids can release hormones that cause other systemic effects, such as Cushing syndrome (from ectopic ACTH production) or abnormal blood calcium or sodium levels.

What conditions are associated with typical carcinoid tumor of the lung?

Typical carcinoid tumor belongs to a spectrum of lung neuroendocrine tumors that are classified by how aggressively they grow and how likely they are to spread. Understanding where typical carcinoid sits in this spectrum helps explain why the diagnosis and prognosis differ so significantly from other lung cancer types.

• Typical carcinoid tumor (Grade 1) — The most indolent (slow-growing) lung neuroendocrine tumor. Defined by fewer than 2 cell divisions per 2 square millimeters of tumor and no areas of tumor cell death (necrosis). Cured by surgery in the great majority of cases.
• Atypical carcinoid tumor (Grade 2) — An intermediate-grade neuroendocrine tumor. Defined by 2–10 cell divisions per 2 square millimeters, or by the presence of necrosis. Grows more aggressively than typical carcinoid and carries a higher risk of spreading to lymph nodes and distant organs. Learn more about atypical carcinoid tumor of the lung.
• Large cell neuroendocrine carcinoma (Grade 3) — A high-grade neuroendocrine carcinoma with more than 10 cell divisions per 2 square millimeters and prominent necrosis. Behaves aggressively and is treated similarly to small cell carcinoma.
• Small cell carcinoma (Grade 3) — The most aggressive neuroendocrine tumor of the lung. Grows and spreads very rapidly, requiring immediate systemic treatment. Learn more about small cell carcinoma of the lung.

The pathologist’s careful assessment of mitotic activity and necrosis in the tumor specimen is what places a neuroendocrine tumor in the correct category — and this distinction directly determines the prognosis and treatment approach.

How is the diagnosis made?

The diagnosis of typical carcinoid tumor is usually made from a tissue sample obtained by biopsy. Because typical carcinoid tumors often arise near the central airways, they are frequently accessible by bronchoscopy — a procedure in which a thin flexible tube is passed through the mouth into the airways to visualize the tumor and collect a small tissue sample. For tumors in less accessible locations, a CT-guided needle biopsy or fine needle aspiration (FNA) may be used. In some cases, the diagnosis is only confirmed after the entire tumor has been surgically removed and examined in full.

Under the microscope, a pathologist identifies typical carcinoid tumor by its characteristic appearance. The tumor cells are arranged in organized nests, cords, or ribbon-like structures — a pattern reflecting their neuroendocrine origin. The cells are uniform and well-defined, with a moderate amount of pale pink cytoplasm. The most distinctive feature is the appearance of the nucleus inside each cell: the chromatin (the cell’s genetic material) is evenly dispersed in a fine, granular pattern that pathologists describe as “salt and pepper” — resembling tiny dark dots scattered on a pale background. This nuclear appearance is a hallmark of neuroendocrine differentiation and is seen across all lung neuroendocrine tumors.

Two features are essential for making the specific diagnosis of typical carcinoid rather than the more aggressive atypical carcinoid: the pathologist carefully counts the number of mitotic figures — cells caught in the act of dividing — across a standardized area of 2 square millimeters of tumor tissue, and inspects the tumor for any areas of necrosis — patches of dead tumor cells. For the diagnosis of typical carcinoid to apply, the mitotic count must be fewer than 2 per 2 square millimeters, and no necrosis may be present anywhere in the tumor. If the mitotic count is 2 or higher, or if necrosis is present, the tumor is reclassified as atypical carcinoid, which has a significantly different prognosis and may require additional treatment after surgery.

To confirm the neuroendocrine nature of the tumor and distinguish it from other lung tumors that can look similar under the microscope, the pathologist performs immunohistochemistry (IHC) — a laboratory technique using antibodies linked to colored dyes to detect specific proteins within the cells. Typical carcinoid tumors characteristically show positive staining for chromogranin, synaptophysin, and CD56 (proteins produced by neuroendocrine cells), as well as TTF-1 (a lung lineage marker). The Ki-67 proliferation index — a measure of the fraction of cells actively dividing — is typically very low in typical carcinoid, usually below 5%, which reflects the slow-growing nature of these tumors and helps distinguish them from the high-grade neuroendocrine carcinomas (large cell neuroendocrine carcinoma and small cell carcinoma), in which Ki-67 is dramatically higher.

Once the diagnosis is confirmed, imaging — including chest and abdominal CT and DOTATATE PET-CT (a specialized scan that detects somatostatin receptor-positive tumors) — is used to assess the extent of disease and guide treatment planning.

Histologic grade

Typical carcinoid tumor of the lung is classified as Grade 1 (well-differentiated neuroendocrine tumor) in the 2021 WHO Classification of Thoracic Tumors. This is the lowest grade in the lung neuroendocrine tumor classification system and reflects the tumor’s slow cell division rate, uniform cell appearance, and absence of necrosis — the same features that define the diagnosis itself. Because the Grade 1 designation is built into the diagnostic criteria (fewer than 2 mitoses per 2 mm² and no necrosis), all typical carcinoid tumors are Grade 1 by definition.

Grade 1 corresponds to the most favorable behavior within the neuroendocrine tumor family. Patients with Grade 1 tumors have significantly better outcomes than those with Grade 2 (atypical carcinoid) or Grade 3 (large cell neuroendocrine carcinoma, small cell carcinoma) tumors. This grading distinction is one of the most important pieces of information in the pathology report for a patient with a lung neuroendocrine tumor.

Lymphovascular invasion

Lymphovascular invasion (LVI) means that tumor cells have been found within blood or lymphatic vessels — the small channels that carry lymph — in or near the tumor. These vessels can act as pathways for tumor cells to travel to lymph nodes or distant organs.

• Lymphovascular invasion not identified — No tumor cells are seen within vessels near the tumor. This is the expected and favorable finding in typical carcinoid.
• Lymphovascular invasion present — Tumor cells are found within vessels. This is uncommon in typical carcinoid but, when present, is associated with a higher risk of lymph node involvement and may influence decisions about the extent of surgery and follow-up.

Pleural invasion

The pleura is the thin membrane that covers the outer surface of the lungs and lines the inside of the chest cavity. Pleural invasion means tumor cells have grown into the pleural layers.

• Pleural invasion not identified — The tumor has not extended to the pleural surface. This is the expected finding for most typical carcinoid tumors, which are usually small and centrally located.
• Visceral pleural invasion — Tumor cells have grown through the elastic layer of the pleura covering the lung surface. This increases the T stage and may be associated with a higher risk of recurrence.

Surgical margins

Surgical margins are the cut edges of the tissue removed during the operation. The pathologist examines all margins to determine whether the tumor was completely removed.

• Negative margin — No tumor cells are seen at the cut edge of the tissue. This is the most favorable result and indicates the tumor was fully excised.
• Close margin — Tumor cells are present very near the cut edge but do not reach it. Depending on the location and distance, further treatment may be discussed.
• Positive margin — Tumor cells are present at the cut edge. This raises concern that some tumor remains and may lead to discussion of additional surgery or radiation therapy to the area.

Lymph nodes

Lymph nodes are small immune organs distributed throughout the chest. During surgery for a lung carcinoid tumor, the surgeon typically removes lymph nodes from specific locations within the lung and central chest — called lymph node stations — and sends them to the pathologist for examination.

The pathology report will describe the total number of lymph nodes examined, their station locations, and whether any contain tumor cells. In typical carcinoid, lymph node involvement occurs in approximately 5–15% of cases, less commonly than in atypical carcinoid or the high-grade neuroendocrine carcinomas. When lymph node involvement is found, it influences the nodal stage and may affect decisions about the extent of surgery and the need for additional treatment or closer surveillance.

Biomarker and molecular testing

The biomarker testing landscape for typical carcinoid tumor is different from that of non-small cell lung cancer. Typical carcinoid tumors do not harbor the targetable driver mutations — such as EGFR mutations or ALK rearrangements — that guide treatment decisions in lung adenocarcinoma. Instead, the most clinically relevant biomarkers relate to somatostatin receptor expression, which influences both staging imaging and treatment eligibility, and molecular features that identify hereditary risk.

Somatostatin receptor expression

Somatostatin receptors are proteins on the surface of neuroendocrine tumor cells that bind a hormone called somatostatin. Approximately 80–90% of typical carcinoid tumors express these receptors — most often somatostatin receptor subtype 2 (SSTR2). This expression has two important clinical consequences.

First, it enables a specialized nuclear imaging technique called DOTATATE PET-CT (using a radioactive tracer that binds to somatostatin receptors), which is highly sensitive for detecting carcinoid tumors and their spread throughout the body. DOTATATE PET-CT is now the preferred staging and surveillance imaging modality for lung carcinoid tumors and is far more sensitive than conventional CT for identifying small tumor deposits in lymph nodes or distant sites.

Second, somatostatin receptor expression makes the tumor eligible for treatment with somatostatin analogs — drugs such as octreotide (Sandostatin LAR) and lanreotide (Somatuline Depot) — which can control hormone-related symptoms (such as carcinoid syndrome) and have been shown to slow tumor growth in metastatic, somatostatin receptor-positive neuroendocrine tumors. Somatostatin receptor expression can be assessed by immunohistochemistry on the tumor biopsy or surgical specimen, as well as by DOTATATE PET-CT imaging.

Everolimus

Everolimus (Afinitor) is an oral targeted drug that blocks a growth signaling pathway called mTOR (mammalian target of rapamycin), which is abnormally active in many neuroendocrine tumors. Everolimus is approved for the treatment of progressive, well-differentiated neuroendocrine tumors of lung origin, based on the RADIANT-4 trial, which showed significantly longer progression-free survival compared to placebo in patients with advanced lung and gastrointestinal neuroendocrine tumors. Everolimus is an option when the tumor has grown or spread despite other treatments. It does not require a specific biomarker test for eligibility — the approval applies to well-differentiated NETs of lung origin, which include typical carcinoid.

Germline testing for MEN1

Because typical carcinoid tumors can be the first sign of Multiple Endocrine Neoplasia Type 1 (MEN1) — an inherited condition caused by mutations in the MEN1 gene — your doctor may recommend referral to a genetic counselor, particularly if you have multiple lung carcinoid tumors, a personal history of MEN1-associated tumors (parathyroid, pancreatic, or pituitary), or a family history suggesting MEN1. Identifying an MEN1 mutation has important implications not only for you but for your family members, who may benefit from genetic testing and surveillance for MEN1-associated tumors.

For more information about biomarker testing in cancer, visit the Biomarkers and Molecular Testing section of MyPathologyReport.

Pathologic stage (pTNM)

Typical carcinoid tumor of the lung is staged using the TNM system based on AJCC 8th edition criteria. The T category describes the size of the tumor and whether it has grown into nearby structures. The N category indicates whether cancer has spread to nearby lymph nodes. The M category — which describes spread to distant organs — is determined by imaging rather than the pathology specimen and is typically not reported in the surgical pathology report. Together, T, N, and M are combined to determine an overall stage, ranging from I (earliest) to IV (most advanced).

Tumor stage (pT)

• pT1a — Tumor is 1 cm or smaller, surrounded by lung or visceral pleura, with no involvement of the main bronchus.
• pT1b — Tumor is larger than 1 cm but no larger than 2 cm, otherwise meeting T1a criteria.
• pT1c — Tumor is larger than 2 cm but no larger than 3 cm, otherwise meeting T1a criteria.
• pT2a — Tumor is larger than 3 cm but no larger than 4 cm; or the tumor — regardless of size — has grown into the visceral pleura, involves the main bronchus without reaching the carina, or is associated with partial lung collapse.
• pT2b — Tumor is larger than 4 cm but no larger than 5 cm, otherwise meeting T2a criteria.
• pT3 — Tumor is larger than 5 cm but no larger than 7 cm; or the tumor has grown into the chest wall, phrenic nerve, or parietal pericardium; or a separate tumor nodule is present in the same lobe as the primary tumor.
• pT4 — Tumor is larger than 7 cm; or the tumor has grown into major structures such as the heart, large blood vessels, trachea, esophagus, or spine; or a separate tumor nodule is present in a different lobe of the same lung.

Nodal stage (pN)

• pNX — Lymph nodes were not examined.
• pN0 — No tumor cells found in any lymph nodes examined.
• pN1 — Tumor cells found in lymph nodes within the lung or near the main airway on the same side of the chest (intrapulmonary, hilar, or peribronchial nodes; stations 10–14).
• pN2 — Tumor cells found in lymph nodes in the central chest on the same side (ipsilateral mediastinal or subcarinal nodes; stations 4–9).
• pN3 — Tumor cells found in lymph nodes on the opposite side of the chest or in the lower neck (contralateral mediastinal, contralateral hilar, scalene, or supraclavicular nodes). This indicates advanced nodal disease.

What is the prognosis?

The prognosis for typical carcinoid tumor of the lung is excellent compared to other lung cancers. When the tumor is completely removed by surgery, five-year survival rates exceed 90% for localized disease (stage I or II). Even when lymph node involvement is present, outcomes remain significantly better than for other lung cancer types, reflecting the inherently slow-growing nature of Grade 1 neuroendocrine tumors.

Factors that influence prognosis include:

• Surgical margins — Complete removal with negative margins is the most important determinant of long-term outcome. A positive margin is associated with a higher risk of local recurrence.
• Lymph node involvement — Nodal metastasis increases the stage and is associated with a higher risk of distant recurrence, though outcomes are still substantially better than for other lung cancers with nodal involvement.
• Confirmation of Grade 1 classification — The excellent prognosis applies specifically to tumors meeting the criteria for typical carcinoid. If atypical features are identified on the surgical specimen, the tumor may be reclassified as Grade 2 atypical carcinoid, which carries a meaningfully worse prognosis.
• Lymphovascular invasion — When present, is associated with a modestly higher risk of nodal and distant spread.
• Distant metastasis — Rare in typical carcinoid but does occur, most often to the liver, bone, or adrenal glands. Even with metastatic disease, patients with typical carcinoid can survive for many years, given the slow growth rate of these tumors.

Long-term surveillance is important even after successful surgery, because late recurrences — occurring more than five years after resection — are reported in a minority of patients with typical carcinoid. Annual CT and periodic DOTATATE PET-CT imaging are typically recommended.

What happens after the diagnosis?

Surgery to completely remove the tumor is the primary treatment for typical carcinoid tumor of the lung and is curative in the great majority of patients. The type of surgery depends on the size and location of the tumor and the patient’s overall lung function.

For tumors arising within a central airway, a bronchoplastic procedure — also called a sleeve resection — may be possible. This technique removes the segment of airway containing the tumor and reconnects the remaining airway ends, preserving more functional lung tissue than a standard lobectomy. For tumors that cannot be reached surgically in the conventional sense, bronchoscopic resection — removal through the bronchoscope — may occasionally be appropriate for small, entirely endobronchial tumors, though careful patient selection is required to ensure complete removal. For most tumors, lobectomy (removal of an entire lobe) or segmentectomy (removal of a defined anatomical lung segment) is the standard surgical approach, performed by a thoracic surgeon using minimally invasive techniques (video-assisted thoracoscopic surgery, VATS) where feasible.

For the small proportion of patients with metastatic or progressive disease that cannot be surgically removed, treatment options include:

• Somatostatin analogs — Octreotide LAR or lanreotide, given by injection every 28 days, control carcinoid syndrome symptoms and can slow tumor growth in somatostatin receptor-positive tumors.
• Everolimus (Afinitor) — An oral targeted therapy approved for progressive, well-differentiated neuroendocrine tumors of lung origin.
• Peptide receptor radionuclide therapy (PRRT) — A targeted radiation treatment using a radioactive molecule (lutetium-177 DOTATATE / Lutathera) that binds to somatostatin receptors on tumor cells and delivers radiation directly to them. PRRT is approved for somatostatin receptor-positive gastroenteropancreatic NETs and is used in lung carcinoids in clinical practice, particularly for progressive disease after other options.
• Clinical trials — Several new treatment approaches for neuroendocrine tumors are under active investigation, and your oncology team can advise whether a trial is appropriate.

After surgery, regular follow-up is essential because late recurrences can occur. A typical surveillance approach includes annual CT of the chest and abdomen, along with periodic DOTATATE PET-CT imaging, for at least 10 years after resection. Blood and urine tests for chromogranin A and 5-hydroxyindoleacetic acid (5-HIAA) — markers released by neuroendocrine tumor cells — may also be monitored at follow-up visits.

Questions to ask your doctor

• Is my tumor confirmed as a typical carcinoid (Grade 1), and were any features of atypical carcinoid found?
• What was the mitotic count, and were any areas of necrosis identified in my tumor?
• What is my pathologic stage, and what does it mean for my prognosis?
• Were the surgical margins clear? If not, what are the next steps?
• Were any lymph nodes found to contain tumor cells, and does this affect my treatment plan?
• Was lymphovascular invasion identified in my pathology report?
• Was somatostatin receptor expression tested, and am I eligible for somatostatin analog therapy or DOTATATE PET imaging?
• Should I have a DOTATATE PET-CT scan as part of my staging or follow-up?
• Do I or my family have features that suggest I should be evaluated for MEN1 syndrome?
• What follow-up schedule is recommended, and for how long?
• What symptoms of recurrence should I watch for between appointments?
• Are there clinical trials I might be eligible for now or if the disease returns?