*Purpose: Explant pathology (EP) is an important prognostic factor after liver transplantation (LT) for hepatocellular carcinoma (HCC). The purpose of this study was to correlate EP findings with outcomes following LT over a 10-year period in a region 5 institution.

*Methods: All LT cases with HCC on EP from Jan. 1, 2010 through Dec. 31, 2019 were identified. Retrospective review was conducted and the following data collected: EP including size, number, histology and differentiation of the tumor(s) as well as the presence of lymphovascular invasion. Additional data included patient demographics, pre-operative imaging and outcomes. Survival was analyzed using the standard Kaplan-Meier method. Separate analysis was conducted for patients in whom HCC was an incidental finding.

*Results: 285 patients met the above inclusion criteria including 19 (6.7%) who did not have a formal diagnosis of HCC pre-operatively. Among the 19 patients, 3 had suspicious lesions, 1 had an elevated serum alpha-fetoprotein with a negative imaging study, and the remaining 15 patients had no evidence of HCC. Among the 16 patients with no radiographic lesions, the incidental tumor on explant was small (Median 1.2cm, Average 1.3cm [0.8cm to 2cm]) with the median value of one tumor per patient (average 1.5). 6 patients had well-differentiated HCC, and the remaining 10 had moderately differentiated HCC. Overall, these 19 patients had an excellent survival when compared to all the study patients as a group (Figure 1). Among the 285 explants, 239 met Milan criteria (MC), and 46 patients did not for the following reasons: lymphovascular invasion (n=20), number and/or size of tumors or local direct invasion (n=14), and non-HCC tumors (n=12). Patients who met the MC had 1 and 5-year survivals of 95% and 90% compared to 78% and 62% for those who did not meet the MC (p < 0.0001) (Figure 2). Survival analysis of the 3 sub-groups showed that those patients with non-HCC or microscopic invasion had a significantly worse outcome than those who did not meet the MC due to the tumor's macroscopic features alone (Figure 3).

*Conclusions: Incidental HCC on EP did not appear to have a negative survival impact likely due to the early nature of the cancer disease. Among the patients who did not meet the MC, those with non-HCC or microscopic invasion had a worse outcome, suggesting that tumor biology and evidence of microscopic invasion are more critical prognostic factors than macroscopic aspects of the tumor including direct local extrahepatic invasion.

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