Role of preoperative irradiation in prolonging concomitant immunity and preventing metastasis in mice

As long as a primary allogeneic tumor was present on a mouse's foot it sustained the concomitant immunity of the host and suppressed the growth of implants of the same tumor. A mouse's immunity to reimplantation of the tumor waned perceptibly within 4 days of the time the tumor was removed, and by the seventh day was barely demonstrable. When the primary tumor was treated by a single large dose of irradiation, its cells, though doomed to die, either released large amounts of sensitizing antigens or continued for from 2 to 3 weeks to produce antigens and sustain the host's immunity against reimplantations of the tumor. In an isogeneic tumor system, the incidence of pulmonary metastasis was much less after destruction of a tumor-bearing foot by irradiation than when the foot was amputated. This suggests that even an isogeneic tumor confers some immunity on the host, and that the rapid waning of this immunity after amputation of the tumor-bearing foot renders the host more susceptible to the development of metastases than it is following its destruction by irradiation.