How can a tumor in the liver be identified and diagnosed?

Include biopsy. As noted, imaging of a lesion >2cm with an elevation of AFP is diagnostic of hepatocellular carcinoma. Depending on the type of lesion, MRI and triple-phase contrast ct can suggest diagnoses, but usually a biopsy is required depending on the level of clinical suspicion and the context to make an actual diagnosis. Detection by itself is most sensitive by intraoperative ultrasound.
Scans. Ultrasound, ct scan with contrast and mri, MRI being the most accurate for anything greater than 2cm. A blood test for AFP can detect hepatocellular carcinoma as well.