Medullary Carcinoma of the Colon and Rectum
Differential Diagnosis
| Colorectal Medullary Carcinoma | Colorectal Poorly Differentiated Carcinoma NOS |
| Lacks any gland formation | At least 5% gland formation |
| Uniform small to medium sized nuclei | Pleomorphic large nuclei |
| Uniformly prominent nucleoli | Variable nucleoli |
| Pushing border | Infiltrative border |
| Prominent lymphoid infiltrate in virtually all cases | Lymphoid infiltrate variable |
| Colorectal Medullary Carcinoma | Colorectal Undifferentiated Carcinoma NOS |
| Lacks any gland formation | May have <5% gland formation |
| Uniform small to medium sized nuclei | Pleomorphic large nuclei |
| Uniformly prominent nucleoli | Variable nucleoli |
| Pushing border | Infiltrative border |
| Prominent lymphoid infiltrate in virtually all cases | Lymphoid infiltrate variable |
| Colorectal Medullary Carcinoma | Poorly Differentiated Neuroendocrine Carcinoma, Large Cell Type |
| Chromogranin and synaptophysin at most focal or scattered | Chromogranin or synaptophysin must be positive in at least 20-50% of cells |
| Vesicular nuclei | Chromatin finely granular, stippled |
| Prominent nucleoli | Inconspicuous nucleoli |
| Does not form rosettes | May form rosettes |
