Increased metabolic activity of indolent liver metastases after resection of a primary colorectal tumor

In murine models, resection of a primary tumor leads to increased vascularization and accelerated growth of metastases that previously had remained microscopic. To study such a potentially inhibitory effect of primary tumors on the outgrowth of distant metastases in humans, we assessed the metabolic activity of liver metastases by F-18-FDG PET before and after resection of primary colorectal tumors. Methods: Group A consisted of 8 patients with synchronous colorectal liver metastases who were scheduled for resection of their primary tumor. These patients underwent an F-18-FDG PET scan shortly before resection and 2-3 wk after resection of the primary tumor. The patients in a control group (group B, n = 9) underwent an F-18-FDG PET scan at the time of diagnosis of the liver metastases and a second scan several weeks later, before initiating treatment. There was no surgical intervention between the two F-18-FDG PET scans in this group. Results: In group A, the maximum and mean standardized uptake values of the liver metastases clearly increased after resection of the primary tumor, by 38% +/- 55% and 42% +/- 52%, respectively, as compared with the first F-18-FDG PET scan. In group B, the maximum and mean standardized uptake values of the second F-18-FDG PET scan were not significantly higher than those of the first F-18-FDG PET scan; -11% +/- 23% and 1% +/- 29%, respectively. The difference in standardized uptake value increase between the 2 groups was statistically significant (P < 0.05). Conclusion: Our data cannot differentiate between the immunologic sequels caused by the surgical trauma itself and those caused by removal of the primary tumor. The observation itself, however, of increased metabolic activity after surgical resection of the primary tumor may have direct clinical applications and suggests the administration of antiangiogenic therapy after surgery of the primary tumor.