Is immunosuppression at the tumor site mechanism of evasion of a systemic response?

BACKGROUND

Some of the questions still open to investigation are: 1) Does the clinical appearance of a tumor nodule require a prior overwhelming of a systemic host response? 2) Does a palpable growing tumor cause host immunosuppression?

MATERIALS AND METHODS

Observation of tumor growth and regression in syngeneic and allogeneic murine models under various experimental conditions. Autopsy studies of allogeneic mice with terminal progressive tumor growth.

RESULTS

In syngeneic systems, the take of a threshold tumor inoculum is not facilitated by the contralateral take and growth of a simultaneously injected ten-fold larger inoculum. In syngeneic models with a growing tumor, implantation of a threshold inoculum of the same tumor on the contralateral side is not facilitated, actually it is significantly suppressed (p > or = 0.003), compared to control mice. In early or moderately advanced stages of allogeneic tumor growth, a contralateral threshold inoculum is not facilitated, it is modestly suppressed (p = 0.04 and P = 0.05). A skin graft from the strain syngeneic to the growing tumor is rejected as rapidly in mice bearing a progressive growth as in mice without tumor or prior contact with the latter. Autopsy studies of allogeneic mice moribund from locally progressive B16 melanoma (known to metastasize early on and widely in the syngeneic host) revealed that 50% of mice had no detectable metastases, while 20% had a single pulmonary metastasis and 30% had multiple pulmonary metastases.

CONCLUSIONS

The initial appearance and growth of a tumor nodule does not involve overwhelming of a putative systemic host response. There is no systemic (general or specific) immunosuppression caused by a progressive tumor in its early or intermediate stages which apparently succeeds in growing through a local immunosuppression at its site of growth.