Malignant transformation of hepatocellular adenoma: how frequently does it happen?

Hepatocellular adenoma is a very rare disease in Japan, and institutions encounter only a limited number of cases. This is one of the reasons for the current skepticism in Japan over whether hepatocellular adenoma can truly undergo malignant transformation to hepatocellular carcinoma. However, hepatocellular adenoma is highly prevalent in Western countries, particularly in Europe, and textbooks from these countries have long noted that hepatocellular adenoma carries risks of bleeding and malignant transformation. Most of the cases of hepatocellular carcinoma routinely encountered in Japan occur as a result of chronic liver injury from viral disease, and it is extremely rare to encounter liver cancer that has developed from hepatocellular adenoma in healthy liver. It would be no exaggeration to say that this is almost never seen. Therefore, a survey and literature review was conducted to assess how many cases of hepatocellular adenoma actually undergo malignant transformation in Japan.