I had a cat scan and my doctor said they found a mark on my liver. what can these be?

Benign lesions: Incidental marks/spots on the liver are commonly seen on ct scans. Spots under 2 cm are almost always benign unless there is a known history of cancer or chronic liver disease. The most common spot is a cyst. Cyst is a benign collection fluid.

Depends: Odds are a benign finding. Most important question is: did you have prior scan and was it compared? Ultrasound or MRI may be suggested but may not always be necessary. Cysts, blood vessel or fatty tumors, malformations are possible though each may have specific radiology test that can confirm best.