Rectal Carcinoid Tumor

• Most common site of colonic carcinoid is rectum

• Gross: usually < 5 mm, round, no ulceration

• Morphology

  • Islands, trabeculae, glands or sheets of monotonous cells.

  • Scant, pink granular cytoplasm and round-oval stippled nuclei, small nucleoli.

  • Minimal pleomorphism, minimal mitotic activity; rarely mucin secretion or anaplasia; no necrosis

• Positive stains: chromogranin, synaptophysin, neuron specific enolase, PAP (80%), CEA, hCG

• Negative stains: PSA

• DDX: prostate carcinoma (PSA+, neuroendocrine markers-)

• 5 year survival 90%. Poor prognosis: 2 cm or larger, invasion of muscularis propria, 2+ mitotic figures/HPF, angiolymphatic invasion, anaplasia.

• Treatment: local excision; partial colectomy if malignant potential.

Reference: pathologyoutlines.com

IHC 1: synaptophysin

IHC 2: chromogranin A