Expansile invasive growth pattern is definite evidence for the diagnosis of small hepatocellular carcinomas: a comparative study of 37 cases

Small HCCs, including seHCC and spHCC, are rarely encountered in daily practice. Definite diagnosis is difficult for general pathologists. In this study, we reviewed 1025 cases of HCC and examined the histologic characteristics of small HCCs to facilitate more accurate diagnosis. Slides of archived HCC cases were reviewed by 2 senior pathologists, and small HCCs were identified according to the canonical criteria. Additional immunohistochemical stains were performed. Thirty-seven cases of small HCC were identified, including 22 cases of seHCC and 15 cases of spHCC. We found 2 types of invasive growth patterns in these lesions. The first is the expansile invasive growth pattern, with monomorphic tumor cells penetrating through the incomplete fibrous capsules and expanding into the adjacent noncancerous liver with a spherical, hemispheric, or mushroom shape. The second is the classic stromal invasion pattern. At least one type of invasive pattern was observed in all of the 37 cases of small HCC, and the seHCCs exhibit the expansile invasive growth pattern more frequently than the classic stromal invasion pattern. On the contrary, stromal invasive pattern was more common in spHCC nodules. In conclusion, with the background of chronic hepatitis and cirrhosis, histologic features including crowdedness of hepatocytic trabeculae and the expansile invasive growth pattern are strong evidence for the diagnoses of small HCC.