The differential diagnosis of poorly differentiated carcinoma of the colon include:
- Poorly differentiated adenocarcinoma
- Medullary carcinoma of the colon &
- Large cell neuroendocrine carcinoma
Medullary carcinoma will usually have sheets, nest or trabecular of small to medium sized cells with a pushing border and a lymphocytic infiltrate with Crohn’s like lymphoid aggregates at the tumour edge. Negative for neuroendocrine markers. Associated with microsatellite instability.
Poorly differentiated adenocarcinoma may show areas with glands.
Neuroendocrine carcinoma – positivity to CD56, synaptophysin & chromogranin.