Improvements and limitations of the subrenal capsule assay for determining tumour sensitivity to cytostatic drugs.

Cyclophosphamide (CY) prevented the host response from occurring in treated animals, and we therefore evaluated CY and other immunosuppressive forms of pretreatment in normal mice using the subrenal capsule assay initially for transplanted and later also for primary tumours. CY pretreatment, 4 or 4.5 Gy whole-body irradiation and cortisone were superior to silica in reducing host cell infiltration, and irradiation as pretreatment has become our routine technique. The addition of cortisone acetate to irradiation was of minor benefit in only 1/3 transplanted lines. When primary tumours were tested, the irradiation was only rarely able to completely prevent cellular infiltration. Only 7/11 ovarian tumours and 3/9 lung tumours were evaluable as tumour specimens (greater than 50% tumour) in preirradiated mice. The degree of infiltration and fibrosis was similar in transplants in irradiated normal mice or in athymic nude mice, suggesting that these phenomena are largely due to properties of the tumours rather than of the host. The limitations of the technique to some cell lines and occasional primary tumours is obvious.