Surgical Pathology Criteria

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

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