Hyperbaric Oxygen and Radiotherapy of a Fibrosarcoma and of a Squamous-cell Carcinoma of C3H Mice
Experimental studies on the efficacy of exposing mice to high-pressure oxygen at the time of local irradiation of transplanted tumors have been extended to include a fibrosarcoma and a squamous-cell carcinoma, both of which had been induced in C3H mice by methylchol-anthrene applications. Previous reports described results in studies of two mouse mammary carcinomas, one originating in a C3H mouse and the second in a DBA mouse (1–4). Results of those investigations may be summarized as follows: (a) large tumors (≈250 mm3) which had areas of grossly necrotic tissue were employed; (b) respiration of pure oxygen at three atmospheres of pressure absolute for fifteen minutes affected the tumor-lethal response to single-dose irradiation by only a slight degree; (c) however, when the treatments were given in 10 equal doses, using a twenty-four-hour interval between treatments, the respiration of high-pressure oxygen was highly effective in increasing the efficacy of local tumor irradiation. Because of the pertinence of animal tumor data of this type to our planning of a clinical trial of high-pressure oxygen and radiation therapy, similar studies have been completed, using tumors of two different histologic patterns: a fibrosarcoma and a squamous-cell carcinoma. Ideally, the present study would have been based on early generation transplants of a “spontaneously” arising fibrosarcoma and a squamous-cell carcinoma. Unfortunately, such tumors were not available. To induce tumors of these histologic patterns, mice were subjected to special treatments with methylcholanthrene. Despite the fact that these chemically induced tumors undoubtedly carried relatively strong specific antigens, they were useful experimental tools in estimating the relative effectiveness of radiation administered during respiration of either oxygen at high pressure or air at one atmosphere of pressure. There is no evidence, known to authors, which suggests that respiration of oxygen at the pressures employed in our experiments, and for brief periods, would modify the immunological reactivity of the host. Materials and Methods Experimental Animals: Young adult female mice of the C3H/He strain (mammary tumor agent-positive) were obtained from the Texas Inbred Mouse Company, Houston, Texas, and were employed in the carcinogenesis experiments. To serve as recipients of the transplants of the induced tumors, (C3H/He × C57)F1 hybrid or C3BF1 mice of both sexes were obtained from the same source. Animal Tumors: Fibrosarcoma: For induction of sarcomas, 13 C3H/He female mice received 0.1 ml of peanut oil containing 1 mg/cc of methylcholanthrene as an injection into the flank subcutaneous tissue. In all the animals tumors developed at the site of injection.