A biopsy of the left colonic mass revealed colonic mucosa infiltrated by poorly differentiated carcinoma based upon the interpretation of immunostaining for anti-cytokeratin (CAM 5.2) as weakly positive as well as negative immunostaining for caudal-type homeobox 2 (CDX2), SRY-box transcription factor 10 (SOX-10), and B-cell-specific activator protein (PAX-5). The gene discussed is SOX10; the disease is carcinoma.