The liver is a highly vascularized organ which frequently hosts metastases in patients with colorectal adenocarcinomas. The hypothesis of this study is that the hypoxic drive of angiogenesis might be minimal or absent in those growing liver metastases which are capable of preserving the stromal structure, including the numerous sinusoidal blood vessels. Representative paraffin sections of liver metastases from 26 patients with colorectal adenocarcinoma were investigated. Three different growth patterns were found. In the desmoplastic and in the pushing growth patterns (42% and 46% of all metastases, respectively), the architecture of the liver parenchyma was not preserved. In the replacement growth pattern (12% of all cases), the reticulin pattern of the liver parenchyma was conserved within the metastases at the tumour-liver parenchyma interface. The endothelial cells of the blood vessels near the interface in the metastases of the replacement type did not express CD34, nor were they surrounded by alpha-smooth muscle actin-positive mural cells. In the desmoplastic and in the pushing growth patterns, 23% and 52% of all blood vessels in this area were covered by pericytes. The fraction of proliferating endothelial cells was low in the metastases with a desmoplastic or a replacement growth pattern (about 3%), compared with metastases with a pushing growth pattern (11%). Tumour cell apoptosis was highest in the pushing-type metastases and was inversely correlated with microvessel density in liver metastases. The ratio of the proliferating tumour cell fraction and the proliferating endothelial cell fraction, roughly representing the degree of angiogenesis-dependent growth, was three- to four-fold higher in the replacement-type metastases compared with the other metastases. In summary, the present study has demonstrated that liver metastases are a heterogeneous group, with different growth patterns which predict the fraction of immature blood vessels, the fraction of proliferating endothelial cells, and the fraction of apoptotic tumour cells. The replacement growth pattern expands with minimal angiogenesis by co-opting the stroma with the sinusoidal blood vessels of the liver.
Copyright 2001 John Wiley & Sons, Ltd.