Establishment and characterization of a new spontaneous metastasis model of human gastric carcinoma in nude mice.

A poorly differentiated medullary carcinoma of human stomach, designated HY-1, was successfully transplanted to nude mice by either the subcutaneous or intramuscular route for five generations. The transplanted tumor showed spontaneous lung metastases in nearly 100% of KSN and Balb/c female nude mice. There were over 20 visible lung metastatic nodules in KSN and Balb/c nude mice bearing tumors for over 80 days. Immunostaining of type IV collagen and electron microscopy revealed that tumor cells were often in direct contact with basement membrane (BM) of tumor blood vessels in the primary tumor tissue. At the site of contact between tumor cells and vascular BM, focal disappearance of the BM, disruption of endothelial cells and entry of tumor cell clusters into vascular lumen were observed. Immunostaining of 72 kDa gelatinase/type IV collagenase demonstrated that tumor cells expressed this enzyme in their cytoplasm. These results suggest that spontaneous metastasis of this tumor may be partly due to a marked tendency to vascular invasion involving the following sequential events: tumor cell contact with vascular BM, BM degradation possibly by 72 kDa gelatinases and endothelial disruption. This model could be a useful tool for understanding the mechanism of hematogenous metastasis of human gastric cancer.