CEA is the tumour marker for GI tumours and is used as the baseline/follow-up marker in colorectal cancer, so colon cancer is the most likely cause of a raised CEA. However, the sources do not separate 'colon cancer' from 'metastatic rectal cancer' (also colorectal, and metastatic disease gives the highest levels), so E is a defensible alternative. Stomach cancer and UC can raise CEA less commonly; HCC is marked by AFP.