Rectal Carcinoid / Well Differentiated Neuroendocrine Neoplasm / Tumor
Definition
- Low grade neoplasm of the the rectum and distal colon demonstrating neuroendocrine differentiation
Note
- Most other colonic carcinoids arise in the cecum near the ileocecal valve and are considered with the ileal carcinoids
- High grade / poorly differentiated neuroendocrine carcinoma is covered separately
Alternate/historical Names
- Hindgut carcinoid
- Well differentiated (neuro-)endocrine tumor/carcinoma are equivalent terms
Diagnostic Criteria
- Most large intestine carcinoids arise in the rectum with smaller numbers in the descending and sigmoid colon
- Most others are cecal, from near the ileocecal valve
- Such neoplasms share histopathologic and clinical features with ileal carcinoids
- Most cells show evidence of neuroendocrine differentiation
- Synaptophysin stain positive in nearly all cases
- Chromogranin frequently negative in rectal carcinoids
- Argyrophil stain positive in nearly all cases
- Argentaffin frequently negative in rectal carcinoids
- Neuron specific enolase, PGP9.5 and CD56 are sensitive but not specific
- Most well differentiated neoplasms exhibit characteristic cytologic and architectural features
- Round regular nuclei
- Stippled (salt and pepper) chromatin
- Moderate to abundant cytoplasm
- Various growth patterns
- Insular growth pattern
- Round nests of cells
- May palisade
- Trabecular
- Rows and strands of cells
- Cells are “stacked” with their long axis perpendicular to the long axis of the row
- Tubular
- Lined by single layer of uniform cells
- True glands with intracytoplasmic mucin not seen
- May form rosette-like pseudo-glandular structures
- True glands with intracytoplasmic mucin not seen
- Usually involves only base of crypts, leaving mucosa largely intact
- Carcinoids can be subdivided by pattern and secretory products
- L cell glucagon-like peptide and pancreatic polypeptide (PP/PYY) producing carcinoid is the dominant pattern in the rectum
- Predominantly tubular and/or trabecular
- Most produce GLP-1, GLP-2, glycentin, oxyntomodulin, PP/PYY
- Serotonin may be positive (30%)
- Synaptophysin positive, may be chromogranin A negative
- Chromogranin B positive (not detected by most common anti-chromogranin antibodies)
- Argyrophil positive, may be argentaffin negative
- Prostatic acid phosphatase positive in >80% of cases
- Enterochromaffin (EC) cell serotonin producing carcinoid is uncommon in the rectum
- Predominantly insular
- May have S100 positive sustentacular cells around nests (16%)
- Produce serotonin and substance P
- Synaptophysin and chromogranin A positive
- Argentaffin and argyrophil positive
- Frequent invasion
- Muscularis propria and serosa
- May elicit desmoplastic response
Robert V Rouse MD
Department of Pathology
Stanford University School of Medicine
Stanford CA 94305-5342
Original posting / updates: 7/27/10, 12/28/11
