Evidence is circumstantial that in animals and, to some extent, in man, an antitumor immune response may be generated after curative
hyperthermia that leads to disappearance of
metastases (abscopal response) and the acquisition of host immunity. In rodents,
tumor regression after heating does not occur in immunosuppressed hosts, and the
tumor cure rate is significantly reduced by inhibition of macrophage activity with
silica; cured immune rats succumb to
tumor inoculation when immunosuppressed. Quantitative data for cellular and humoral immunocompetence in these situations exist for only a few
tumor types, and the bulk of evidence indicates that host response following
tumor heating is nonspecific in type, with a major macrophage component. Little is distinctive about the regression of heated
tumors, i.e., an abscopal response can follow treatment of
tumors by excision or
hypothermia. In man, an immune response is seldom evoked by the heating of the common solid
tumors. Whole-body heating in animals can cause immunosuppression, probably from a direct damaging effect on lymphoid tissue, and enhanced metastatic spread may follow in the
tumor-bearing host, but this has not been proved in man. The differences in response of
tumors to heat in animals and man may be due to variations in
tumor immunogenicity and host tolerance to heat.