Background. Hepatocellular carcinoma (HCC) ≤2 cm in diameter is considered to have a low potential for malignancy. Methods. A retrospective review was undertaken of 149 patients with primary solitary HCC ≤2 cm who underwent initial hepatic resection between 1994 and 2010. The independent predictors of the microinvasion (MI) such as portal venous, hepatic vein, or bile duct infiltration and/or intrahepatic metastasis were identified by multivariate analysis. Prognosis of patients with HCC ≤2 cm accompanied by MI was compared to that of patients with HCC ≤2 cm without MI. Results. Forty-three patients with HCC ≤2 cm had MI in patients (28.9%). Three independent predictors of the MI were revealed: invasive gross type (simple nodular type with extranodular growth or confluent multinodular type), des-c-carboxy prothrombin (DCP) >100 mAU/ml, and poorly differentiated. Disease-free survival rates of patients with HCC ≤2 cm with MI (3 year 44%) were significantly worse than those for HCC ≤2 cm without MI (3 year 72%). This disadvantage of disease-free survival rate of patients with HCC ≤2 cm with MI could be dissolved by hepatic resection with a wide tumor margin of C5 mm (P = 0.04). Conclusions. Even in cases of HCC ≤2 cm, patients who are suspected of having invasive gross type tumors in preoperative imaging diagnosis or who have a high DCP level (>100 mAU/ml) are at risk for MI. Therefore, in such patients, hepatic resection with a wide tumor margin should be recommended.
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