A mitomycin C-resistant Jensen rat sarcoma: isolation and transplantation studies.

A transplantable rat tumor, the Jensen sarcoma, has been selected for resistance to the action of mitomycin C. Initial treatment consisted of 0.15 mg/kg. After seven passages through rats, the treatment dose was raised to 0.5 mg/kg. Under normal cir cumstances, this dose of antibiotic completely inhibits tumor growth. The stability of this resistance was proved by passage of the tumor through more than twenty genera tions in untreated rats. The antibiotic-resistant tumor was also found to have the following character istics: (a) growth as a firm mass with less necrosis and central liquefaction than is ordi narily observed in the sensitive sarcoma; (6) a greater tendency to persist for longer periods of time in the rat host before showing drastic signs of regression; (c) a slow growth rate in cortisone-treated Swiss mice; (d) poor transplantability to neonatal mice; and (e) cross-resistance to nitrogen mustard in tests with the cortisone-treated Swiss mouse.