Rare variants of primary liver cancer: Fibrolamellar, combined, and sarcomatoid hepatocellular carcinomas.

Hepatocellular carcinoma (HCC) constitutes 80% of all primary liver cancers. Based on key developments in the understanding of its carcinogenesis and the advancement of treatment options, detailed algorithms and practice guidelines have been published to guide the clinical management of HCC. Furthermore, several subclasses of HCC have been described based on molecular profiles and linked to pathological characteristics, clinical features, and disease aggressiveness. Most recently, the combination of the checkpoint inhibitor atezolizumab plus bevacizumab has significantly increased treatment response in the first line systemic treatment of HCC. Unfortunately, rare HCC variants, in particular fibrolamellar liver cancer (FLC), combined hepatocellular carcinoma and cholangiocarcinoma (cHCC-CCA), and sarcomatoid hepatocellular carcinoma (sHCC), were excluded from phase III studies. Therefore, data for decision-making and treatment allocation for these distinct entities, representing 1-5% of all primary liver cancers, is scarce. Moreover, most of the knowledge available for these rare HCC variants is based on registry data and retrospective studies. In this position paper, we briefly summarize the current clinical knowledge regarding FLC, cHCC-CCA, and sHCC. Based on our summary, we propose future clinical research activities within the framework of the European Reference Network on Hepatological Diseases (ERN RARE-LIVER).