Tumor cells transfected with the neomycin resistance gene (neo) contain unique genetic markers useful for identification of tumor recurrence and metastasis.

Studies in tumor biology often require techniques to accurately identify tumors or tumor cell lines. Transfection of plasmid DNA into mammalian cells has been shown to introduce unique genetic markers into recipient cells. These unique genetic markers are detected by Southern transfer. To determine the usefulness of such markers for in vivo studies, a bacterial gene, neo, was transfected into mouse and guinea pig tumor cells. Inbred mice and guinea pigs were injected with syngeneic tumor lines marked with neo. DNA extracted from primary and recurrent tumors and metastases was tested for the presence of the characteristic markers. Integration of neo in cell lines was shown to be stable during tumor growth, recurrence and metastasis, and therefore to be useful for identification of tumors growing in vivo.