Induction of Lung Cancers in Animal S

This paper presents clinical, experimental, and epidemiologic evidence to help explain the rapidly increasing incidence of primary lung cancer, with recently observed reversal in leading cell type from squamous cell to adenocarcinoma. It postulates that this may be due to changes in modern cigarettes, with or without filters, which allow inhalation of increased amounts of radioactive lead and polonium and decreased amounts of benzopyrene . This hypothesis is based upon measurements of increased concentrations of radioactive polonium in the lungs of cigarette smokers, in modern tobaccos grown since 1950, and in high-phosphate fertilizers used for tobacco farming in industrialized countries . Critical support for this thesis is based upon experimental animal studies in which lung cancers that resemble adenocarcinomas are induced with as little as 15 rads of radioactive polonium, equal to one fifth the dosage inhaled by cigarette smokers who average twb packs a day during a 25-year period . f PARADOXICALLY, the incidence of lung cancer has greatly increased in the past two decades even though 15 Jo of the population (30 million Americans) have quit smoking. In addition, 90% of American cigarettes now have filters that reduce concentrations of tars and nicotine in the smoke.' 2 Nevertheless, age-adjusted death rates show that twice as many American men died of lung cancer in 1980 than in 1960, and three times as many women . 3 Because at least 85% of lung cancers are reported to occur in cigarette smokers, the major carcinogens must be within the cigarettes themselves .4 Furthermore, incidences of lung cancer are directly proportional to daily cigarette consumptions CRITERIA FOR MAJOR TOBACCO CARCINOGENS Whatever the major tobacco carcinogens, they should prove to be inadequately filtered by cigarette filters and small doses should cause lung cancers in experimental animals . Greater concentrations of these chemicals should be found in the lungs of cigarette smokers than in nonsmokers, and there should be some reason for an increased concentration of these carcinogens in tobacco smoke . 'Read before the Section on Chest Diseases . Southern Medical Association . 78th Annual Scientific Assembly, New Orleans, La . Nov 4-7 . 19114 . From the Department of Internal Medicine, University of Southern Calilornsa College of Medicine, and Santa Barbara Cottage Hospital . Santa Barbara. Calif. Reprint ecquests to femme Marmorstein . MD. 601 E Arrcllaga. Suite 202, Santa Barbara, GA 93103 . INDUCTION OF LUNG CANCERS IN ANIMAL S Of more than 100 carcinogens found in cigarette smoke, three types of substances have been shown to cause lung cancers by inhalation or tracheal instillation into experimental animals .' Since 1957, polyaromatic hydrocarbons such as benzopyrene have been shown to cause lung cancers in experimental animals .6 Benzopyrene caused squamous cell cancers of the lung when it was instilled into the respiratory tracts of hamsters and mice . However, benzopyrene's concentration in tobacco smoke has been greatly reduced in the last 20 years by changes in tobacco processing and use of filters .' Therefore, benzopyrene seems unlikely to be responsible for the continued increase in lung cancer, especially adenocarcinoma . Several nitrosamines found in trace amounts of tobacco smoke can also induce respiratory cancers in experimental animals, but with greater difficulty . Furthermore, since 80% of nitrosamines are eliminated by cigarette filters, these chemicals should be of decreased importance . ' RADIOACTIVE POLONIUM The only other carcinogen in tobacco smoke shown to cause lung cancers in experimental animals is radioactive polonium, which emits the most powerfully carcinogenic form of radiation known, alpha radiation .'-8 Of the three tobacco carcinogens, radioactive polonium is the least reduced by cigarette filters and is the only one shown to cause lung cancers in animals by actual inhalation (Table 1) .9.1 0 Radioactive polonium is completely volatized Marmorstein • LUNG CANCER AND CIGARETTES 145 http://legacy.library.ucsf.edu/tid/uuc38a99/pdf