Carcinoid Tumors

Slide 1 · Carcinoid Tumors

Pulmonary neuroendocrine neoplasms

Morphology • Grading • Clinical consequences

Dr Abu Suraih Sakhri

MBBS, MD (Pathology)

www.abusuraihsakhri.com

Slide 2 · Learning objectives

Place pulmonary carcinoids within the neuroendocrine spectrum of lung lesions.

Recognize characteristic gross and microscopic growth patterns.

Apply Robbins morphologic criteria for typical versus atypical carcinoids.

Explain how bronchial obstruction, secretory activity, and tumor spread shape clinical findings.

Slide 3 · Normal pulmonary neuroendocrine cells

Normal airway epithelium contains scattered neuroendocrine cells.

These cells may occur singly or in clusters termed neuroepithelial bodies.

This cell lineage provides the background for the pulmonary neuroendocrine spectrum.

Typical

Lower-grade morphology

Atypical

Intermediate-grade morphology

Slide 4 · Reactive neuroendocrine cell hyperplasia

Most pulmonary neuroendocrine hyperplasias accompany airway fibrosis or inflammation.

Their association with damaged airways distinguishes reactive proliferation from an independent neoplasm.

Do not automatically classify every neuroendocrine cell cluster as a carcinoid tumor.

Clinicopathologic interpretation

The surrounding airway pathology is part of the interpretation: Inflammatory scarring is a common setting for reactive hyperplasia.

Slide 5 · Diffuse idiopathic hyperplasia: The exception

Diffuse idiopathic pulmonary neuroendocrine cell hyperplasia is rare.

Unlike most hyperplasias, it occurs without an inflammatory stimulus.

This as an exception to the usual reactive setting.

Clinicopathologic interpretation

“Idiopathic” identifies the absence of a recognized inflammatory trigger in the supplied source, not a molecular cause.

Slide 6 · Tumorlets: The benign end of the spectrum

Tumorlets are small nests of pulmonary neuroendocrine cells.

They are usually encountered with scarring or chronic inflammation.

These as benign and inconsequential compared with malignant neuroendocrine tumors.

Clinicopathologic interpretation

Site, extent, and tissue context separate a small benign tumorlet from a clinically significant pulmonary mass.

Slide 7 · Pulmonary neuroendocrine spectrum

Hyperplasia

Usually fibrosis / inflammation

Tumorlet

Small benign nests

Carcinoid

Typical or atypical

Carcinoma

Small cell or large cell NEC

The entities belong to one cellular lineage but differ markedly in clinicopathologic behavior.

Slide 8 · Why carcinoids form a separate category

Carcinoids are distinguished from highly aggressive pulmonary neuroendocrine carcinomas.

They differ in incidence, clinical and epidemiologic behavior, histology, and molecular characteristics.

A shared neuroendocrine phenotype does not imply equivalent clinical aggressiveness.

Clinicopathologic interpretation

Neuroendocrine differentiation is a lineage feature; Malignant potential and grade require separate assessment.

Slide 9 · Definition: Pulmonary carcinoid tumor

A pulmonary carcinoid is a low-grade malignant epithelial neoplasm with neuroendocrine differentiation.

It is subdivided into typical and atypical carcinoids.

The word “malignant” recognizes the potential for local invasion and metastasis even when the course is indolent.

Typical

Lower-grade morphology

Atypical

Intermediate-grade morphology

Slide 10 · Frequency within lung neoplasms

Carcinoids as 1%–5% of all lung tumors.

They are less common than conventional bronchogenic carcinomas.

The proportion is a descriptive textbook estimate, not a patient-level probability.

Clinicopathologic interpretation

Reported textbook frequency: 1%–5% of lung tumors. Denominator is all lung tumors; No registry year or method is specified.

Slide 11 · Age and sex distribution

Most affected patients are younger than 60 years.

Incidence is approximately equal in both sexes in the Robbins description.

Neither age nor sex establishes the diagnosis without morphology.

Clinicopathologic interpretation

Demographic trends contextualize a clinical presentation, but do not substitute for histologic classification.

Slide 12 · Smoking exposure is not universal

Approximately 20%–40% of patients in the cited source are nonsmokers.

Pulmonary carcinoids therefore must not be dismissed solely because tobacco exposure is absent.

The textbook passage does not define a smoking-related molecular pathway.

Clinicopathologic interpretation

History is supportive contextual information—not a prerequisite for identifying a carcinoid.

Slide 13 · Two anatomic settings

Carcinoids may arise in central conducting bronchi or more peripherally.

Central lesions commonly project into the bronchial lumen.

Peripheral lesions are more often solid nodules.

Location

Central or peripheral

Appearance

Polypoid or nodular

Consequence

Obstruction or incidental lesion

Slide 14 · Central tumors: Polypoid growth

Central bronchial carcinoids form finger-like or spherical polypoid masses.

They project into the lumen and may narrow the airway.

A gross description should capture the endobronchial component and any wall extension.

Bronchial wall

Lumen

Schematic — conceptual, not a specimen

Slide 15 · Why the overlying mucosa matters

The mucosal covering is commonly intact, despite the underlying tumor mass.

A smooth surface does not exclude an epithelial neoplasm.

This distinction is important when linking bronchoscopic appearance to histology.

Bronchial wall

Intact mucosa

Lumen

Schematic — conceptual, not a specimen

Slide 16 · Mainstem bronchial location

Most centrally situated lesions are confined to mainstem bronchi.

A centrally positioned mass is especially capable of obstructing a large airway.

Record the relationship between the lesion and the bronchial lumen.

Bronchial wall

Lumen

Schematic — conceptual, not a specimen

Slide 17 · Gross size: A useful description

Central carcinoids rarely exceed 3–4 cm in the Robbins description.

Size describes the mass but does not by itself distinguish typical from atypical histology.

Mitotic activity and necrosis remain the source-defined grading criteria.

Clinicopathologic interpretation

Do not convert this typical gross size into a diagnostic cutoff or an eligibility threshold.

Slide 18 · Growth can cross the bronchial wall

Some lesions penetrate the bronchial wall into peribronchial tissue.

The endobronchial and extrabronchial components may coexist.

This explains why the full gross extent can exceed the lumen-facing polypoid portion.

Bronchial wall

Lumen

Schematic — conceptual, not a specimen

Slide 19 · Collar-button lesion

Robbins calls a polypoid component with outward peribronchial spread a “collar-button” lesion.

The name describes the gross shape and relationship to the bronchial wall.

It is a configuration—not a separate carcinoid grade or molecular subtype.

Bronchial wall

Lumen

Schematic — conceptual, not a specimen

Slide 20 · Peripheral carcinoids

Peripheral pulmonary carcinoids are described as solid, nodular masses.

They lack the conspicuous lumen-projecting growth of central lesions.

Central versus peripheral is an anatomic distinction, not a grading system.

Peripheral lung parenchyma

Solid nodule

Schematic — conceptual, not a specimen

Slide 21 · Central and peripheral lesions: Gross comparison

Feature

Central bronchial lesion

Peripheral lesion

Predominant shape

Polypoid; Finger-like or spherical

Solid, nodular

Relationship to lumen

Often protrudes into a bronchus

May not be endobronchial

Typical mucosal finding

Often intact over the tumor

Not the defining feature

Functional consequence

Potential airway obstruction

Depends on location / extent

Slide 22 · Gross assessment: What to document

Localize the mass as central or peripheral.

Describe polypoid versus solid-nodular configuration.

Record mucosal covering and extension through the bronchial wall.

Do not assign typical/atypical status from gross appearance alone.

Clinicopathologic interpretation

Gross examination establishes location and extent; The typical–atypical distinction comes from microscopy.

Slide 23 · Microscopy: A recognizable architecture

Neoplastic cells form organoid nests, trabeculae, palisades, ribbons, and rosettes.

These arrangements are separated by delicate fibrovascular stroma.

A single tumor can show more than one neuroendocrine architectural pattern.

Schematic — conceptual, not a specimen

Slide 24 · Organoid arrangement

Tumor cells are grouped in cohesive, organ-like nests.

A fine supportive stromal network separates the nests.

This pattern is one of several morphologies compatible with pulmonary carcinoid.

Schematic — conceptual, not a specimen

Slide 25 · Trabecular architecture

Tumor cells may form elongated cords or trabeculae.

Intervening fibrovascular tissue separates the cellular strands.

Architecture suggests neuroendocrine differentiation but is not an independent grade criterion.

Schematic — conceptual, not a specimen

Slide 26 · Palisading architecture

Cells may align in palisading arrays.

This directional organization belongs to the textbook architectural repertoire.

Assess mitoses and necrosis independently of the attractive palisaded pattern.

Schematic — conceptual, not a specimen

Slide 27 · Ribbon-like growth

Cells may form curved, elongated ribbons.

Ribbon-like arrangements can coexist with organoid or trabecular structures.

Recognition is useful when sampling is small and a classic nest is absent.

Schematic — conceptual, not a specimen

Slide 28 · Rosette-like arrangements

Tumor cells can organize around small central spaces in a rosette-like configuration.

This is another manifestation of neuroendocrine morphology.

A rosette-like pattern alone does not establish the typical versus atypical category.

Schematic — conceptual, not a specimen

Slide 29 · Delicate fibrovascular stroma

A thin fibrovascular framework separates the tumor cell aggregates.

This architecture differs from a single uniform solid sheet of cells.

Observe the relationship between cellular nests, vascular spaces, and stromal septa.

Schematic — conceptual, not a specimen

Slide 30 · Cytology: Relatively uniform cells

The original figure description emphasizes small, rounded, uniform nuclei.

Tumor cells have moderate cytoplasm.

Cytologic uniformity fits a well-differentiated carcinoid pattern but does not replace formal grading.

Schematic — conceptual, not a specimen

Slide 31 · An integrated microscopic reading

First, recognize the neuroendocrine architectural pattern.

Second, assess cytology, mitotic activity, and necrosis.

Third, examine for disorganized growth and lymphatic invasion.

The final typical/atypical category follows morphology, not a single visual impression.

Clinicopathologic interpretation

Architecture and grade provide different information: Pattern establishes character; Mitoses and necrosis help classify it.

Slide 32 · Pulmonary carcinoid grading is morphologic

Grading using histologic criteria.

Typical and atypical categories correspond approximately to lower and intermediate neuroendocrine grades.

Proliferation-marker measurement is not required in the source-defined lung system.

Clinicopathologic interpretation

Do not import a Ki-67-based grade from gastrointestinal or pancreatic neuroendocrine tumors.

Slide 33 · Mitotic activity: The formal denominator

The Robbins criteria are stated as mitoses per 10 high-power fields (HPF).

Typical carcinoid: Fewer than 2 mitoses per 10 HPF.

Atypical carcinoid: 2–10 mitoses per 10 HPF and/or necrosis.

Use the specified field denominator when quoting this textbook.

Clinicopathologic interpretation

This lecture reports the 11th-edition textbook wording. Field area calibration and current reporting standards are not provided in the excerpt.

Slide 34 · Necrosis changes the classification

Typical carcinoids lack necrosis.

Foci of necrosis support the diagnosis of atypical carcinoid.

Necrosis is a formal histologic discriminator, not merely a descriptive afterthought.

Clinicopathologic interpretation

A tumor with low mitotic activity but focal necrosis falls into the atypical category under the stated “and/or” criterion.

Slide 35 · Typical carcinoid: Qualifying morphology

Organized neuroendocrine architecture may be present.

Mitotic rate is fewer than 2 per 10 HPF.

Necrosis is absent.

Clinical behavior is generally more favorable than that of atypical carcinoid.

Schematic — conceptual, not a specimen

Slide 36 · Atypical carcinoid: Qualifying morphology

Mitotic rate is 2–10 per 10 HPF and/or focal necrosis.

Cytologic pleomorphism and nucleolar prominence may increase.

Growth can be less organized, and lymphatic invasion is more likely.

Schematic — conceptual, not a specimen

Slide 37 · Atypical cytology: Additional clues

Atypical carcinoids may display increased pleomorphism.

Nucleoli may be more prominent.

These changes support the overall impression but the defined distinction still rests on mitoses and/or necrosis.

Clinicopathologic interpretation

Avoid assigning atypical grade on cytologic appearance alone if the defining information is missing.

Slide 38 · Disorganized growth and lymphatic invasion

Atypical carcinoids are more likely to show disordered architecture.

Lymphatic invasion is more frequent in the atypical group.

Invasion is a biologic warning; It should be separately documented from mitoses and necrosis.

Clinicopathologic interpretation

Lymphatic invasion indicates a route for dissemination but does not establish distant metastasis by itself.

Slide 39 · Typical versus atypical carcinoids

Characteristic

Typical carcinoid

Atypical carcinoid

Mitoses / 10 HPF

< 2

2–10; Fewer if necrosis is present

Necrosis

Absent

Focal necrosis may occur

Cell pleomorphism

Generally less conspicuous

May be increased

Nucleoli

Usually less prominent

May be more prominent

Growth / invasion

Relatively organized

More disorganization; More lymphatic invasion

Reported 5-year survival

95%

70%

Slide 40 · Ki-67: A system-specific distinction

The lung carcinoid scheme is based on morphologic criteria.

It does not currently require proliferation markers such as Ki-67.

Other organ systems may use proliferation markers differently; Do not transfer those rules uncritically.

Clinicopathologic interpretation

“Not required for grading” does not mean a proliferation index could never be measured for a separate clinical purpose.

Slide 41 · Ultrastructure: Dense-core granules

On electron microscopy, carcinoid cells contain dense-core neurosecretory granules.

The granules support neuroendocrine differentiation.

They are not identified by H&E pattern alone.

Clinicopathologic interpretation

The electron-microscopy finding is reported in the source; The slide uses no synthetic EM image.

Slide 42 · Immunohistochemical evidence of secretion

Immunohistochemical detection of serotonin and other products.

Listed examples include neuron-specific enolase, bombesin, and calcitonin.

Different tumors can express different substances; One peptide does not define every carcinoid.

Clinicopathologic interpretation

These are examples in the supplied Robbins passage, not an exhaustive modern immunohistochemical panel.

Slide 43 · Marker role must be interpreted correctly

Evidence of neuroendocrine differentiation helps characterize the tumor lineage.

Histologic mitoses and necrosis, not any listed secretory peptide, define typical versus atypical in this source.

The ability to produce a peptide does not guarantee a clinical secretory syndrome.

Clinicopathologic interpretation

Keep lineage markers, grading criteria, and functional secretion as separate diagnostic questions.

Slide 44 · Morphologic grading: A decision framework

Neuroendocrine morphology

Recognize architecture

Assess mitoses

Count per 10 HPF

Assess necrosis

Absent or present

Typical carcinoid

<2 mitoses / 10 HPF AND no necrosis

Atypical carcinoid

2–10 mitoses / 10 HPF AND/OR necrosis

Apply this distinction only after establishing pulmonary carcinoid morphology.

Slide 45 · Three mechanisms of clinical disease

Intraluminal growth can impair airway patency and drainage.

Some tumors can metastasize.

A minority can produce vasoactive amines and a systemic syndrome.

The mechanisms must be evaluated separately in individual patients.

Clinicopathologic interpretation

Mechanical obstruction, dissemination, and hormone-mediated symptoms are distinct clinical pathways.

Slide 46 · Persistent cough: Local airway effects

Cough is one manifestation of intraluminal bronchial growth.

A central mass can alter the airway lumen without a large external lung lesion.

Correlate cough with the bronchial location, not with endocrine secretion by default.

Bronchial wall

Lumen

Schematic — conceptual, not a specimen

Slide 47 · Hemoptysis: Another local manifestation

Hemoptysis appears among the source-described symptoms of bronchial carcinoids.

A lesion projecting into the bronchial lumen may present with visible airway bleeding.

The symptom does not by itself distinguish typical from atypical carcinoid.

Bronchial wall

Lumen

Schematic — conceptual, not a specimen

Slide 48 · Impaired drainage causes secondary infection

A lumen-occupying tumor can compromise distal airway drainage.

Retained secretions can be associated with infection beyond the obstruction.

In such presentations, the apparent infectious problem may coexist with an underlying tumor.

Clinicopathologic interpretation

A localized infection pattern should prompt consideration of the bronchial obstruction mechanism when supported by imaging or bronchoscopy.

Slide 49 · Bronchiectasis downstream of obstruction

Bronchiectasis among consequences of bronchial carcinoid obstruction.

The associated airway change may reflect prolonged impairment of drainage and recurrent injury.

Describe bronchiectasis as a secondary manifestation, not as the histologic grade.

Clinicopathologic interpretation

Mechanistic explanation of prolonged drainage impairment is inferential; The association itself is source stated.

Slide 50 · Emphysema may accompany an obstructing lesion

Emphysema is among the reported complications of intraluminal carcinoid growth.

Airway narrowing may produce regional abnormalities in ventilation.

The source does not specify an imaging pattern or quantify the risk.

Clinicopathologic interpretation

Do not claim a particular radiologic subtype of emphysema solely from this textbook list.

Slide 51 · Atelectasis: A consequence of blocked airflow

Atelectasis is listed among the complications of bronchial luminal obstruction.

Loss of airway patency can be associated with distal loss of aeration.

Intraluminal tumor growth can therefore have effects larger than the mass itself.

Clinicopathologic interpretation

Local anatomic disturbance and distal functional effect should be interpreted together.

Slide 52 · Mechanical obstruction: Clinicopathologic cascade

Bronchial mass

Endoluminal component

Reduced patency

Poor airflow / drainage

Secondary injury

Infection or atelectasis

Other associated effects: Cough, hemoptysis, bronchiectasis, and emphysema.

Slide 53 · Metastatic potential must not be forgotten

Although usually low-grade, pulmonary carcinoids have malignant potential.

Clinical manifestations can result from their capacity to metastasize.

A relatively indolent course does not make staging or follow-up irrelevant.

Clinicopathologic interpretation

Atypical carcinoids show more lymphatic invasion in the source, supporting greater concern for dissemination.

Slide 54 · Functional tumors: Endocrine activity

Some carcinoids contain functional cells capable of elaborating vasoactive amines.

Secretory activity can produce symptoms remote from a mass in the bronchus.

Most bronchial carcinoids are not functionally secretory description.

Clinicopathologic interpretation

Tumor presence and clinical secretory activity are different properties.

Slide 55 · Vasoactive mediators in carcinoid syndrome

Serotonin and bradykinin are associated with carcinoid syndrome in the adjacent Robbins paraneoplastic section.

Amines or related mediators can generate systemic vasomotor and intestinal symptoms.

Do not infer a specific analyte concentration or laboratory threshold from this excerpt.

Clinicopathologic interpretation

The source names mediators but provides no biochemical diagnostic algorithm.

Slide 56 · Carcinoid syndrome: Clinical manifestations

Classic pulmonary carcinoid syndrome can produce intermittent diarrhea.

Episodic flushing is another characteristic manifestation.

Cyanosis is also included in the Robbins triad.

The syndrome is a functional phenomenon rather than a measure of tumor grade.

Clinicopathologic interpretation

In the Robbins source: Intermittent diarrhea + flushing + cyanosis.

Slide 57 · How often is the syndrome reported?

Approximately 10% of bronchial carcinoids produce carcinoid syndrome.

Therefore, the syndrome is not present in the large majority of cases.

Absence of flushing or diarrhea does not exclude the tumor.

Clinicopathologic interpretation

The 10% figure is the book-reported estimate; It is not a diagnostic sensitivity estimate.

Slide 58 · Avoid conflating local and systemic symptoms

Cough, hemoptysis, and postobstructive infection chiefly reflect local bronchial growth.

Diarrhea, flushing, and cyanosis indicate a potential mediator-driven syndrome.

Metastatic disease represents a third pathway with separate consequences.

Clinicopathologic interpretation

One patient may have overlapping mechanisms; Classify symptoms by the underlying process.

Slide 59 · Clinical course is often indolent

Most bronchial carcinoids neither secrete clinically significant products nor metastasize distantly.

Many follow a relatively benign course over prolonged periods.

The course is nonetheless heterogeneous: Histologic subclassification matters.

Clinicopathologic interpretation

“Relatively benign course” must not be rewritten as a universal absence of malignant risk.

Slide 60 · Surgical resection and disease extent

Because many pulmonary carcinoids remain localized, they are often amenable to resection.

Intraluminal location and wall extension are relevant to operative assessment.

The source does not provide a regimen-specific treatment algorithm.

Clinicopathologic interpretation

The textbook supports the general resectability statement—not particular operative techniques or guideline-based treatment thresholds.

Slide 61 · Reported survival differs by carcinoid subtype

Robbins quotes 95% five-year survival for typical carcinoids.

The corresponding reported value for atypical carcinoids is 70%.

These are descriptive textbook rates and not individual patient predictions.

Clinicopathologic interpretation

The excerpt does not specify stage distribution, treatment, study population, or confidence intervals.

Slide 62 · Context: Survival across pulmonary neuroendocrine tumors

95%

Typicalcarcinoid

70%

Atypicalcarcinoid

30%

Large cellNE carcinoma

5%

Small cellcarcinoma

Robbins-reported five-year survival

Slide 63 · What the prognostic contrast demonstrates

Typical and atypical carcinoids have substantially better reported outcomes than neuroendocrine carcinomas.

Typical carcinoid has the more favorable course of the two carcinoid grades.

A survival percentage summarizes groups; It cannot substitute for individual staging and clinical context.

Clinicopathologic interpretation

The four percentage values come from one Robbins comparison; Avoid claiming a causal effect of any particular therapy.

Slide 64 · Application case: A central endobronchial mass

Hypothetical scenario: Persistent cough, intermittent hemoptysis, and a smooth polypoid bronchial lesion.

Question: Which gross characteristics favor pulmonary carcinoid as a diagnostic consideration?

Reason through lumen projection, mucosal covering, and potential obstruction.

Bronchial wall

Intact mucosa

Lumen

Schematic — conceptual, not a specimen

Slide 65 · Application case: Interpret histologic grading

Hypothetical tumor: Organoid/trabecular growth, 1 mitosis per 10 HPF, and no necrosis.

What carcinoid category follows morphologic criteria?

Which measured findings carry grading weight, and which are architectural clues?

Schematic — conceptual, not a specimen

Slide 66 · Application case: Low mitoses with focal necrosis

Hypothetical tumor: A carcinoid pattern with 1 mitosis per 10 HPF but focal necrosis.

Question: Does the low mitotic count alone justify “typical” carcinoid?

Apply the source’s “and/or” formulation for the atypical category.

Clinicopathologic interpretation

The focal necrosis means the case should not be labeled typical using the provided criteria.

Slide 67 · Application case: Intermittent systemic symptoms

Hypothetical patient: An endobronchial carcinoid with episodic flushing and diarrhea.

Question: Which clinical mechanism differs from simple airway obstruction?

Explain why the absence of this syndrome in another patient would not refute carcinoid.

Clinicopathologic interpretation

The hormonal syndrome is uncommon (~10%) and mechanism-distinct from bronchial obstruction.

Slide 68 · Common classification errors to avoid

Do not use an intact bronchial mucosa to declare the mass benign.

Do not grade a pulmonary carcinoid solely with Ki-67.

Do not equate a rosette-like pattern with typical carcinoid.

Do not overlook focal necrosis when mitoses are low.

Do not assume that every carcinoid causes carcinoid syndrome.

Slide 69 · Integrated diagnostic summary

Recognize a pulmonary neuroendocrine lesion through site, architecture, and cytology.

Assign typical or atypical using mitoses and necrosis as.

Assess local obstruction, dissemination, and functional secretion as separate clinical axes.

Relate subtype to the broadly different textbook-reported outcomes.

Slide 70 · Source and interpretive limits

Primary text: Robbins, Cotran & Kumar, Pathologic Basis of Disease, 11th ed. (2026), “The Lung,” pp. 658–659.

Parent context: “Neuroendocrine Proliferations and Tumors,” p. 658; mediator list: “Paraneoplastic Syndromes,” p. 657.

Diagrams illustrate gross and cellular organization; they are schematics rather than actual histologic specimens.

The typical/atypical distinction is morphologic; site and clinical presentation supply complementary information.