Mucin in Primary Liver Carcinomas: Combined Hepatocellular‐Cholangiocarcinoma or Variant Hepatocellular Carcinoma

OBJECTIVE: To investigate whether the presence of mucin defines a combined hepatocellular‐cholangiocarcinoma or merely a variant of usual hepatocellular carcinoma (HCC). METHODS: From 1979‐92, 124 cases of usual HCC were studied at Niigata University Hospital, Niigata City, Japan, and several affiliated hospitals. Histological diagnoses were determined according to World Health Organization (WHO) criteria. Hematoxylin and eosin stain, periodic acid‐Schiff (PAS) stain, PAS stain after diastase digestion (D‐PAS) and silver stain tests were performed. Cases containing D‐PAS‐positive substances were also stained by Alcian blue (AB) stain, high iron diamine (HID) stain and concanavaline A paradox‐3 type (ConA3) stain. The classification of mucin was determined by AB, HID and ConA3 stains. RESULTS: Mucin was recognized in the area of HCC by mucin stains in 25 of 124 cases. Two forms of mucin existence were classified: extracellular and intracellular. Mucins were classified by histochemical stains into three types: sulfomucin, sialomucin and neutral mucin. CONCLUSIONS: According to the WHO histological classification of primary carcinoma of the liver, mucin existence is characteristic of intrahepatic cholangiocarcinoma. But if mucin exists in morphologically usual HCC, it is better to diagnose it as a variant of HCC (with mucin) rather than as a combined hepatocellular‐cholangiocarcinoma.