Introduction

Previously, hepatocellular carcinoma (HCC) was a major problem only in Asian and African countries, but it has become a common problem for gastroenterologists, radiologists, and pathologists in Western countries as well. Until 30 years ago most HCCs were detected at an advanced stage, and the survival time after diagnosis was no longer than 1 year. Remarkable advances in clinical diagnostic approaches, in particular the development of various diagnostic imaging techniques and the establishment of a follow-up system for high-risk populations, have made it possible to detect small HCCs at an early stage. The characteristic clinicopathologic features of early-stage HCC, which are very different than those of classical advanced-stage HCC, have now been well documented in humans, and much has been discovered about the process of hepatocarcinogenesis and the morphological evolution from early to advanced HCC. The most characteristic pathological feature of small early-stage HCCs, up to around 2.0 cm in diameter, is that many of them are well differentiated. Such well-differentiated small HCCs are not yet encapsulated and contain portal tracts inside the nodule, meaning that they receive portal blood supply as well. Well-differentiated HCCs at the early stage show dedifferentiation along with an increase in tumor size, and many HCCs larger than 3 cm become moderately differentiated and show the clinicopathologic features of classical HCC.

Pathology of hepatocellular carcinoma

The establishment of a follow-up system for patients at high risk for the development of hepatocellular carcinoma and advances in diagnostic imaging techniques in recent years have led to the detection of an increasing number of small nodular lesions of the liver.