Definition/General

Introduction:
-Gastric carcinoid tumors are neuroendocrine neoplasms arising from enterochromaffin-like (ECL) cells
-They represent 1-2% of gastric tumors
-Three distinct types based on pathogenesis
-Cytological diagnosis requires recognition of neuroendocrine features.
Origin:
-Arise from ECL cells in gastric mucosa
-Type I: Associated with chronic atrophic gastritis
-Type II: Associated with MEN-1, Zollinger-Ellison syndrome
-Type III: Sporadic, most aggressive.
Classification:
-WHO 2019 classification: Grade 1 (G1), Grade 2 (G2), Grade 3 (G3)
-Type I (70%): Hypergastrinemia, multiple small tumors
-Type II (5%): MEN-1 associated
-Type III (25%): Sporadic, large solitary.
Epidemiology:
-Peak age 50-60 years
-Female predominance (Type I)
-Equal gender distribution (Type III)
-Increasing incidence
-Associated with PPI use.

Clinical Features

Presentation:
-Often asymptomatic
-Dyspepsia
-Abdominal pain
-GI bleeding
-Carcinoid syndrome (rare)
-Incidental finding.
Symptoms:
-Epigastric discomfort
-Nausea
-Early satiety
-Anemia
-Flushing (rare)
-Diarrhea (rare).
Risk Factors:
-Chronic atrophic gastritis
-H
-pylori infection
-Pernicious anemia
-MEN-1 syndrome
-Long-term PPI use.
Screening:
-Chromogranin A levels
-Gastrin levels
-Endoscopic surveillance
-MEN-1 screening.

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Gross Description

Appearance:
-Small polypoid lesions (Type I, II)
-Large solitary mass (Type III)
-Yellow-brown color
-Smooth surface
-Multiple lesions (Type I).
Characteristics:
-Firm consistency
-Well-circumscribed
-Homogeneous cut surface
-No necrosis (G1, G2)
-Central necrosis (G3).
Size Location:
-Fundus and body (Type I, II)
-Any location (Type III)
-Size <1 cm (Type I)
-Size >3 cm (Type III).
Multifocality:
-Multiple tumors (Type I, II)
-Single tumor (Type III)
-Synchronous lesions
-Metachronous development.

Microscopic Description

Histological Features:
-Uniform round cells
-"Salt and pepper" chromatin
-Moderate cytoplasm
-Organoid pattern
-Trabecular arrangement
-Nested pattern.
Cellular Characteristics:
-Round to oval nuclei
-Finely granular chromatin
-Inconspicuous nucleoli
-Eosinophilic cytoplasm
-Cellular uniformity
-Neuroendocrine granules.
Architectural Patterns:
-Organoid nests
-Trabecular cords
-Rosette formation
-Solid sheets
-Ribbon pattern
-Perivascular arrangement.
Grading Criteria:
-Grade 1: <2 mitoses/10 HPF, Ki-67 <3%
-Grade 2: 2-20 mitoses/10 HPF, Ki-67 3-20%
-Grade 3: >20 mitoses/10 HPF, Ki-67 >20%.

Immunohistochemistry

Positive Markers:
-Chromogranin A
-Synaptophysin
-CD56
-Neuron-specific enolase
-Somatostatin receptor 2
-Ki-67 (grading).
Negative Markers:
-Cytokeratins (usually)
-TTF-1
-CDX2
-Calcitonin
-Insulin.
Diagnostic Utility:
-Confirms neuroendocrine differentiation
-Grading assessment
-Differential diagnosis
-Therapeutic targeting.
Molecular Subtypes:
-Type I: Well-differentiated
-Type II: Well-differentiated
-Type III: Variable grade.

Molecular/Genetic

Genetic Mutations:
-MEN1 mutations (Type II)
-TP53 mutations (high-grade)
-RB1 mutations
-ATRX mutations
-DAXX mutations.
Molecular Markers:
-Chromogranin A
-Somatostatin receptors
-mTOR pathway
-Notch signaling.
Prognostic Significance:
-Grade most important
-Size and invasion
-Type classification
-Lymph node status.
Therapeutic Targets:
-Somatostatin analogs
-mTOR inhibitors
-PRRT
-Chemotherapy (high-grade).

Differential Diagnosis

Similar Entities:
-Adenocarcinoma
-Lymphoma
-Stromal tumors
-Metastatic NET
-Reactive changes.
Distinguishing Features:
-NET: Neuroendocrine markers positive
-Adenocarcinoma: Glandular features
-Lymphoma: Hematopoietic markers.
Diagnostic Challenges:
-Small biopsy specimens
-Crush artifacts
-Grade assessment
-Type classification.
Rare Variants:
-Mixed adenoneuroendocrine carcinoma
-Large cell neuroendocrine carcinoma
-Small cell carcinoma.

Sample Pathology Report

Template Format

Sample Pathology Report

Complete Report: This is an example of how the final pathology report should be structured for this condition.

Specimen Information

Gastric cytology, adequate for evaluation

Diagnosis

Neuroendocrine tumor (Carcinoid)

Neuroendocrine Features

Uniform cells with [salt and pepper chromatin] and [organoid pattern]

Grading

Grade: [G1/G2/G3] based on mitotic count and Ki-67

Type Classification

Type: [I/II/III] gastric NET

Special Studies

Neuroendocrine markers: [Chromogranin A+, Synaptophysin+]

Ki-67 index: [percentage]

Final Diagnosis

Gastric cytology: Neuroendocrine tumor, Grade [1/2/3]