Early invasiveness characterizes metastatic carcinoid tumors in transgenic mice.

The conversion of a normal cell into a metastatic tumor is thought to occur in a stepwise progression of genetic changes that affect both growth control and interactions with the extracellular environment. The development of invasiveness allows tumor cells to escape from their primary site. We have investigated transgenic mice that develop both invasive intestinal neuroendocrine tumors and noninvasive tumors of the pancreatic beta-cells. Visual inspection and gene expression studies indicate that the beta-cell tumors rarely metastasize. In contrast, intestinal tumors that first appear in submucosal areas metastasize with high frequency to the lymph nodes and liver. No evidence of preneoplastic mucosal lesions was seen in the intestine, indicating that invasiveness is acquired early in the tumorigenic progression of these cells. Comparison of intestinal and pancreatic neuroendocrine tumors in transgenic mice suggests that an early requirement for invasiveness may contribute to metastatic potential.