Histopathology of the host response to Lewis lung carcinoma: modulation by pyran

The growth and metastasis of sc transplanted Lewis lung carcinoma were inhibited in C57BL/6J mice by treatment with pyran copolymer. The mean volume of the tumors of pyran-treated animals was 15% that of the saline-treated controls at day 33 post transplantation. Thereafter, the carcinomas gradually increased in volume. Pulmonary metastasis was first observed histologically at day 28 after pyran treatment, compared to day 15 after saline administration. All saline-treated animals died by day 48, whereas 70% of those given pyran remained alive. Tumor necrosis was much more extensive in the lesions of pyran-treated mice. Although neutrophils and monocytes, but few lymphocytes, infiltrated the subcutaneous connective tissue above the neoplasms of animals receiving saline, few leukocytes were present in other connective tissue sites around the tumor. In contrast, treatment with pyran was characterized by a shift at an early interval from a predominance of neutrophils to a predominance of histiocytes and some lymphocytes in the connective tissue above and around the subcutaneous tumor. These cells were often closely associated with degenerate-appearing tumor cells. Additionally, activated macrophages removed from the peritoneal cavity of pyran-treated, tumor-bearing mice exhibited nonspecific cytotoxicity for tumor cells in vitro.