Colorectal small cell carcinoma

Definition

Small cell neuroendocrine carcinoma of the colorectum is a rare highly aggressive tumour.

Epidemiology

Most patients are elderly.

Macroscopic appearances

Tumours usually involve the right colon. There is commonly an adenomatous polyp overlying the small cell carcinoma.

Histopathology

The tumour cells are small with scant cytoplasm. Nuclei vary from round to oval to spindle with granular chromatin and inconspicuous nucleoli. There is nuclear moulding. Combined tumours also show an adenocarcinomatous component.

Immunohistochemistry

Cytokeratins		15/151
NSE		14/141
CD56		8/151
Chromogranin		9/151
Synaptophysin		10/141
DNA mismatch repair enzymes	MLH1	14/151
	MSH2	15/151
	MSH6	15/151

Deficiencies of DNA mismatch repair enzymes do not appear to play a role in the aetiology of colorectal small cell carcinoma.

Prognosis

Most cases have metastases at the time of diagnosis. Tumours with a small cell morphology but lacking a neuroendocrine immunophenotype have a less poor prognosis.

References

1 Stelow EB, Moskaluk CA,Mills SE The mismatch repair protein status of colorectal small cell neuroendocrine carcinomas. Am J Surg Pathol 2006; 30:1401-4

This page last revised 5.1.2007.