Application of the polymerase chain reaction (PCR) to quantify micro-metastasis in an experimental animal

In vitro cultured r/mHM-SFME-1 cells were injected into the hind foot pads of Balb/c mice. Metastasis was detected in the lungs of tumor-bearing mice by means of both PCR and histological methods. Primers for the PCR were set to amplify a 128 bp exon-1 sequence of the human c-Ha-ras1 gene which had been introduced into the cells. Resulted PCR bands were densitometorically quantified using a bioimage analyzer, and more than 1 x 10(4) tumor cells were detectable in the mouse lung. The number of tumor cells per lung estimated from the amount of PCR products was 1 x 10(5), 15 x 10(5), 1 x 10(5) and 40 x 10(5) on days 7, 14, 21 and 28 respectively after the tumor injection. No metastases were histologically observed on days 7 and 14. Then, the possibility of using this model system for evaluation of a treatment against micro-metastases is discussed.