Progression of a Weakly Tumorigenic Mouse Fibrosarcoma at the Site of Early Phase of Inflammation Caused by Plastic Plates

To elucidate tumor progression‐enhancing factor(s), we examined the effects of host inflammation and host immunological status on in vivo tumor progression. One × 10 4 cells of QR clones (QR‐32, ‐20 and ‐18), regressor tumor clones of 3‐methylcholanthrene‐induced fibrosarcoma, were unable to grow when injected s.c. into C57BL/6 mice in cell suspension form. However, QR clones grew and were lethal when s.c. implanted, attached to plastic plates. Furthermore, the tumor lines (QRpP) obtained from the tumors which had arisen from the plate‐attached QR‐32 clone cells no longer required plastic plates for their growth in normal mice, and had acquired stable malignant phenotypes. Although QR‐32 cells became lethal when injected at the site of plastic plate implantation 1, 5 and 10 days before tumor injection, few tumors developed when plastic plates had been implanted 20 or 30 days before tumor injection. We established culture clones from the tumors arising in normal mice and mice immunosuppressed by irradiation. Clones derived from the tumors which had arisen in normal mice after implantation with plastic plates were lethal when re‐implanted in normal mice (71%). On the other hand, clones derived from the tumors that arose in irradiated mice with or without plastic plates were lethal in only a few normal mice, when re‐implanted (20 and 8%, respectively). These results indicate that QR clone cell progression is enhanced by the early phase of inflammation at the site of plastic plate implantation and that the progression‐enhancing activity of co‐implantation with a plastic plate is inhibited by previous whole‐body irradiation of hosts.