Interstitial invasion of well-differentiated hepatocellular carcinoma and subsequent tumor growth

Pathological processes of interstitial invasion of hepatocellular carcinoma (HCC) were investigated in 125 autopsy and seven surgical cases, where selection focused on those occurring in well-differentiated HCC. The invasive pattern of well-differentiated HCC was characterized by the formation of streaks of tumor cell cords running along connective tissue fibers, referred to as a streak pattern. These cell cords were unaccompanied by reticulin frameworks and type IV collagen, which are consistent components of HCC parenchyma. The typical streak pattern was observed only in HCC cases and could be useful in differential diagnosis. Following progressive accumulation or proliferation of the tumor cells within the interstitium, many capillaries appeared between the cell cords while collagen fibers tended to disappear. The tumor cell cords then showed branching and were accompanied by reticulin frameworks, type IV collagen and sinusoidal blood spaces. In the setting of interstitial invasion of well-differentiated HCC, it is suggested that interstitial tissue is converted into HCC parenchyma via the aforementioned steps.