INTERSTITIAL TUMOR-CELL INVASION IN SMALL HEPATOCELLULAR-CARCINOMA - EVALUATION IN MICROSCOPIC AND LOW MAGNIFICATION VIEWS

In order to study the process of hepatocellular carcinoma (HCC) develo pment, and to search for a clue to histologic diagnosis of well-differ entiated HCC (wd-HCC), interstitial invasion in small HCC was evaluate d. The study material consisted of 35 cases of HCC that were smaller t han 3 cm that comprised 17 cases of wd-HCC, 18 cases of moderately or poorly differentiated classical HCC (cl-HCC), and 20 cases of large re generative nodules (LRN). Interstitial invasion was microscopically cl assified into three patterns: (i) crossing type, in which HCC was inva ding across fibrous septa of tumour nodules; (ii) longitudinal type, i n which tumour cells were growing longitudinally within fibrous septa; and (iii) irregular type, in which the portal area was irregularly in vaded by HCC. The crossing type was found in two cases (12%) of wd-HCC and 10 cases (56%) of cl-HCC while the longitudinal type was observed in 16 cases (94%) of wd-HCC and eight cases (44%) of cl-HCC. The irre gular type was frequently seen in wd-HCC (15 cases, 88%), and cl-HCC ( 12 cases, 67%). No interstitial invasion was observed in LRN. Intersti tial invasion could be recognized even in the low magnification view o f histological specimens, with a detection rate of 59% (10 cases) in w d-HCC and 72% (13 cases) in cl-HCC. These results suggest that evaluat ion of interstitial invasion is useful in diagnosing wd-HCC independen t of cellular atypia. In addition, such invasive growth is revealed to play an important role in destroying original hepatic architecture du ring its developmental process from the early to advanced stages.