Experimental cancer of the lung in rabbits induced by chemical carcinogens.

Lung cancer was induced in rabbits by the instillation of chemical carcinogens into the lower bronchus, with the use of a bronchoscope. The rabbits were divided into 2 groups. Group 1 received a mixture of 3-methylcholanthrene (3-MCA) and 4-nitroquinoline 1-oxide in rabbit plasma, and Group 2 received 3-MCA alone in distilled water. Doses of 40 mg of 3-MCA and 0.4 mg of 4-nitroquinoline 1-oxide were given every 7 to 10 days. The total doses of carcinogens required for 50% incidence of lung cancer were 1000 ±100 mg of 3-MCA and 10 ±1 mg of 4-nitroquinoline 1-oxide in Group 1 and 1330 ±100 mg of 3-MCA in Group 2. Altogether, lung cancer was induced in 80 of 173 rabbits that received more than 4 doses of carcinogens and survived for more than 30 days. In 55 cases, métastasesand/or invasion of the chest wall and diaphragm were observed. Histologically, the cancers were of various types (e.g., squamous cell carcinomas, adenocarcinomas, undifferentiated cell carcinoma, pleomorphic carcinomas, and mixed types). The main bronchus, in rabbits of another group, was swabbed every 1 to 2 days with cotton wool soaked in a 10% suspension of 3-MCA in Tween 60. Of the 65 rabbits that survived for more than 60 days, only 2 developed lung cancer with métastasesor invasion of tissues adjacent to the lung.