Tumor DNA circulating in the plasma might play a role in metastasis. The hypothesis of the genometastasis

Background: Clinical and experimental observations suggest that more than o ne pathway might be involved in the development of metastases. In the prese nt study, we examined the presence of tumor DNA in plasma using an experime ntal model in which tumor cells were modified with a genome-associated tag. We also investigated whether plasma of tumor-bearing rats had any effect o n cultured cells and healthy animals. Methods: Transfected cancer cells (DH D/K12-PROb stably transfected with pCDNA3.1CAT.) were injected subcutaneous ly into the chest of BD-IX rats. Animals were divided into ten groups accor ding to the time between injection of tumor cells and euthanasia. Prior to euthanasia (2-14 week), blood samples were collected by cardiac puncture. T o detect circulating tumor cells and CAT-encoding DNA in plasma, we perform ed PCR with nested primers. Fifty samples of plasma were chosen at random t o supplement the medium of fifty cultures of DHD cells for 10-12 days. PCR for the detection of CAT DNA in cells was performed approximately one to tw o months later. Four healthy rats received an intraperitoneal injection of plasma from a tumor-bearing rat five times at week for 4 to 6 weeks. Animal s were sacrificed and samples of liver, kidney, spleen, omentum, blood and lung were processed by PCR for the detection of CAT DNA. Results: Detection of CAT DNA in plasma was slightly more frequent than in the buffy-coat fra ction. All surviving cultures that had been supplemented with plasma were p ositive at some point for CAT DNA. In all four healthy animals injected wit h plasma of tumor-bearing rats, the marker gene for CAT was found in extrac ts of lungs. Conclusion: Our present observation lead us to propose the fol lowing hypothesis. Metastases might develop as a result of transfection of susceptible cells in distant target organs with dominant oncogenes that are present in the circulating plasma and are derived from the primary tumor.