GENERAL CHEMICAL AND EXPERIMENTAL DATA ON CARCINOGENESIS AND TOBACCO SMOKE Polynuclear Aromatic Hydrocarbons Ascriteria for the presence of polynuclear aromatic hydrocarbons in tobacco smoke, the list of J. W. Cook (20) has been widely accepted by tobacco chemists. The Surgeon General’s 1964 Report and Cook’s paper are in agree- ment with respect to the presence of benzo(a)pyrene (3: 4-benzopy- rene), dibenz(a,h)-anthracene (1,2: 5,6-dibenzanthracene),’ benzo(c) phenanthrene (3: 4-benzophenanthrene), and dibenzo(a,i)pyrene (3,4: 9,10-dibenzopyrene), all having carcinogenic activity. Cook considers, furthermore, as identified : Benz(a) anthracene (1,2- benzanthracene) marginal carcinogenic activity; chrysene, benzo(e) pyrene (1,2-benzopyrene), questionable carcinogenic activity; benzo (g,h,i)-perylene (1,12-benzoperylene) , benzo(b)fluoranthene (3,4- benzofluoranthene) carcinogenic (59, 106), and benzo(j) fluoranthene (10,11-benzofluoranthene) carcinogenic (106). Indeno (1.2.3-cd) pyrene (2,3-phenylenepyrene) has since been iso- lated from tobacco smoke (45). This polynuclear aromatic hydrocar- bon was found to be carcinogenic (44, 59). The following carcinogens, or questionable carcinogens, were isolated by Kiryu and Kuratsune (55) in the smoke of cigarettes smoked by human volunteers: benz (a)anthracene, chrysene, benzo(a)pyrene, benzo(e) pyrene, benzo(b) fluoranthene and benzo(k)fluoranthene. The carcinogenic polynuclear aromatic hydrocarbons are regarded as the major initiating car- cinogens in tobacco smoke. N-Heterocyclic Aromatic Hydrocarbons The Surgeon General’s 1964 Report lists as carcinogenic compounds three N-heterocyclics, dibenz(a,j) acridine, dibenz(a,h) acridine and 7 H-dibenzo-(c,g)carbazole. An independent investigation has con- firmed the presence of the first named compound in cigarette smoke (107). N-Nitrosamines _N-nitrosamines are among the most powerful known animal car- cinogens. Since tobacco smoke contains secondary amines (57, 71) *Dibenzo (a,h)anthracene in the Surgeon General's 1964 Report should be replaced by dibenz(a,h) anthracene (24). 2 Benzo(g,h,i)perylene was not tested for carcinogenicity until 1966 and then was found to be inactive (44). 127 and most tobaccos, certainly Burley and Maryland varieties, contain nitrates (64), tobacco smoke can be considered as a potential environ- ment for the formation of N-nitrosamines. The major nitrates in tobacco are alkaline nitrates. Neurath, et al., isolated three aliphatic N-nitrosamines from the smoke of a cigarette rich in volatile basic components and high in nitrate content. One of them tentatively has been identified as methy- n-butyl-nitrosamine (72). When the particulate matter, “tar,” was collected from cigarettes not enriched with basic components or when the smoke particulate matter was collected without aging and not in cold traps, N-nitros- amines could not be isolated from cigarette smoke (72). Since the only other publication concerned with the isolation of nitrosamines in cigarette smoke was based on cold trap collection of “tar,” the positive finding of three N-nitrosamines appears questionable (86). In summary, tobacco smoke can be regarded as a potential environ- ment for the formation of N-nitrosamines. However, additional infor- mation is needed to substantiate their presence in tobacco smoke. Polonium 210 _ Several investigators (33, 35, 50, 76, 92, 93, 112) have found trace amounts of Po”! in tobacco leaf and cigarette smoke. The concentra- tion of Po*** in lung tissue is relatively high (33, 67) as compared to other body tissues and is higher in smokers than in nonsmokers (33, 43,65, 66). ; Lung tumors have been induced experimentally by intratracheal implantation of various radioactive substances. These radioactive sub- stances must, however, be present in the respiratory environment above a certain threshold level and must be in contact with the target organ long enough to be effective (68, 77, 88, 107). Because Po?” emits alpha particles, it has been implicated as a lung cancer initiator (48, 68, 76, 77). More research is needed before definitive conclusions can be made. Until such time, however, Po?!° should be considered as a potential tumor initiator in tobacco smoke. Selenium Selenium has been mentioned as possibly being important in the pathogenesis of human lung cancer (100). Preliminary reports suggest that selenium may be present in some cigarette papers. Because earlier reports (17, 34, 97) indicated the ingestion of selenium caused cancer of the liver in mice, a recent investigation (101) by the National Can- cer Institute was conducted, with negative results. So far the earlier reports of the carcinogenicity of selenium have not been substantiated. Additional information is needed on the possible carcinogenicity of selenium and its presence in cigarette smoke before selenium can be indicted as an agent in human cancer. 128 Phenols Tobacco smoke contains a large number of phenols (107). Several of them are known to be tumor promoting agents when applied in high concentrations to mouse skin previously treated with a tumor initiator (24). In Vrrro CeLtuLar CHances By Topacco SMOKE Lasnitzki (60) extended her studies with tobacco smoke condensate on cultured human fetal lung tissue to include a “highly purified fraction of hydrocarbons” isolated from cigarette smoke condensate. In 33 out of 50 treated lung tissue explants, the epithelium of the bronchi was hyperplastic and sometimes showed squamous changes. These changes were not observed with the untreated controls. Although a hydrocarbon-free fraction was weakly active by producing some squamous metaplasia in these explants, these tissue culture tests point strongly to carcinogenic hydrocarbons as the active group in the smoke. The findings with purified carcinogenic hydrocarbons in organ culture (22) support the finding that polynuclear aromatic hydrocarbons are one group of active smoke constituents. Carcinogenic hydrocarbons are also the only group of chemical components that have been demonstrated in vitro to induce malignant conversion of single cells (7, 13). In summary, tobacco smoke has been demonstrated in vitro to induce pathological changes in tissue explants. Although such changes may be induced by different smoke constituents, as yet the carcinogenic hydrocarbons are the only agents identified in tobacco smoke which have been shown to induce malignant changes in’ tissue cultures. In Vivo Tumor Formation sy Topacco SMOKE Passive inhalation experiments with tobacco smoke have not yet led to fully established squamous carcinoma in mice (109). This method of application has resulted only in papillomatous growth in the tracheobronchial mucosa of a few hamsters. None of the tumors, however, was found to be invasive (30, 111). It appears that passive inhalation may not lead to the induction of squamous cell bronchogenic cancer in experimental animals. This conclusion can also be applied to passive inhalation studies in which the animals are infected by a virus before long-term smoke exposure (62, 210). The pathological changes seen in the mice were reversible whether or not the animals were previously infected with a virus. The hyperplasia and metaplasia seen in mice and rats after passive inhalation appears, at least in part, to be secondary to viral or bacterial infection that is enhanced by exposure to tobacco smoke. The relatively negative findings with pas- 129 sive inhalation experiments probably relate to the relatively smal] amounts of smoke aerosols that bypass the nasal passages. The defen- sive nature of the upper respiratory tract against airborne irritants has to be fully appreciated in the evaluation of any passive inhalation study. Active inhalation studies with tracheostomized dogs, as carried out by Rockey, (79, 80) and Auerbach (2), suggest that this approach may lead to the induction of bronchogenic carcinoma. The change in the bronchial epithelium after 1 year of active smoking indicates early pathological changes that may, upon continued smoke exposure lead to tumors in the bronchi. So far, neither passive nor active inhalation studies have contributed to our knowledge about the nature of the tobacco smoke carcinogens. Studies with the particulate matter, tar, of cigarette, pipe, and cigar _ smoke, however, have clearly demonstrated that at the site of applica- tion tumors can be induced. Tumors have been induced on the skin of mice and rabbits, the ears of rabbits, the subcutaneous tissue and hilum of rats and the cervices of mice (9, 11, 22, 31, 32, 46, 48, 61, 74, 82, 83, 8h 107, 108). Only relatively few investigators have been concerned with the nature of chemical carcinogens in tobacco smoke (47, 84, 107). Al- though the acidic and nicotine-free basic portions of tobacco tar had been found to have weak tumorigenic activity, the only fraction shown to have induced significant numbers of tumors is fraction B of the neutral portion (2 percent of the whole condensate) (107). This B fraction was further fractionated into three subfractions from which only B, was shown to have tumorigenic activity (47). The B, frac- tion equals 0.6 percent of the tar and combines all aromatic hydro- carbons with three to seven rings including the carcinogenic ones. This can be considered as evidence that in in vivo studies, the poly- nuclear aromatic hydrocarbons are the major carcinogens in tobacco smoke. Although these compounds alone can account for only a small portion of the tumorigenic activity of tobacco tar, they are, neverthe- less, the only identified carcinogens and tumor initiators in tobacco smoke shown by experimentation to be biologically active. Their tumorigenic effect is enhanced by the presence of tumor-promoting agents in the smoke. Tumor -Promoting AcENTs In Tospacco Propucts In the experimental setting, the tumorigenicity of tobacco smoke condensate cannot be solely explained by the presence of known car- cinogens. In assays on mouse skin and rat subcutaneous tissue, the known carcinogens must be enhanced by other components such as tumor-promoting agents. In fact, it has been demonstrated that to- 130 bacco extract and tobacco smoke condensate can act as promoters to mouse skin previously treated with tumor-initiating carcinogenic polycyclic aromatic hydrocarbons (10, 12, 96, 107). Although some tumor-promoting activity of tobacco “tar” can be explained by some phenols and carboxylic acids, additional tumor promoters in tobacco products remain to be isolated and identified. It is important, however, that a significant decrease of the poly- nuclear aromatic hydrocarbons in tobacco “tar” leads to a significant decrease of the overall activity of the “tar” on mouse skin (9, 46, 108, 109). m summary, experimental studies have demonstrated that the par- ticulate matter of tobacco smoke, “tar,” is tumorigenic. Some poly- nuclear aromatic hydrocarbon-carcinogens have been identified as con- tributing significantly to the overall tumorigenic activity of tobacco smoke condensates in the experimental setting. LUNG CANCER Morrauiry Data* The annual number of deaths in the United States from cancer of the lung (International Classification of Diseases, Codes 162, 163) rose from 18,313 deaths in 1950 to 45,838 in 1964 (94). In this 15-year period, deaths from lung cancer totaled 467,442. During this same time period the death rate for cancer of the lung almost doubled, a rise from 12.2 deaths per 100,000 population in 1950 to 24 deaths per 100,000 population in 1964. (The corresponding age-adjusted rate has also nearly doubled, therefore the increase in the death rate cannot be attributed to the changing age composition of the population.) The lung cancer mortality in the male population increased from 19.9 deaths per 100,000 population in 1950 to 41.4 in 1964, while in the female population the deaths increased from 4.5 to 7.1 per 100,000 population over the same time period. The mortality experience of the individual male cohorts during 1949-64 (fig. 1) shows that at any given age the risk of dying from lung cancer was almost always higher for the more recently born cohort. Within each cohort, the death rate for lung cancer increased steadily to the end of the life span. Figure 2 shows the death rate for women by cohort groups and age at death. One can see the increasing death rate slope for each more recently-born cohort, starting with cohort F—those women who were 26-30 years old in 1930. This corresponds to the time when smoking became increasingly popular among women. 1 AN death rates throughout this chapter are per 100,000 population unless otherwise indicated. 131 SST (76) SOHSHVIG |TVeH 10j JazUeD [BUOWEN : eomN0g 4000 2000 >— g 3 °o I COHORT OF PERIOD OF MALES BIRTH = ° a o NUMBER OF DEATHS PER 100,000 POPULATION » a AOS -1079 -Betore 1875 I | J | ! I ! I I | 40 “4 so 58 60 8 To ws 80 aSene AGE IN YEARS 4000 60.0 200 109 eo 60 40 20 oe oe oe Os Fieurg 1.—Cancer of the lung among men, by birth cohort and age at death; 1949, 1954, 1959, and 1964. eT aainog . (76) BIASHBIP DBI JOJ J9}UVH [BUONEN NUMBER OF DEATHS PER 100,000 POPULATION 1000 1000 800 }— 800 600 600 409 400 200 —200 100 109 sok COWORT OF PERIOD OF leo FEMALES BIRTH of | 6 oI 925=182B 60 1920-1924 4or- 1915-1919 —40 1910-1914 1908-1909 20 .. 1900-1904 20 1895-1899 onuenee es 1BBO= 1894 10 1885-1889 10 oe fh a rn 1aao- 1884 oa ost . 1875-1879 tos De ceeceesenecs reteset - Before 1075 on os az oz ou l 1 | | l l ! | | Ol 20 45 30 38 60 6s 70 75 80 AGE IN YEARS @5 ond over Fucure 2.—Cancer of the lung among women, by birth cohort and age at death: 1949, 1954, 1959, and 1964. In the female population the greatest percentage increase (116 per- cent) over the 15-year period, 1949-64, occurred in the 35-44 year age group. The next highest percentage increase was noted in the age group 45-54 years. The death rate from lung cancer among women, 25 years and over, rose steadily with advance in age for each year during 1950-64, and the cohort experience shows that these death rates continued to increase for each cohort to the end of the life span. Hammond’s (40) prospective study provides extensive information about the lung cancer mortality experience of both men and women in relation to cigarette-smoking history as presented by mortality ratio? and by death rates per 100,000 person-years. (Table 1). TasLe 1.—Lung cancer mortality ratios and death rates * of smokers by sex and specific age groups 45-64 years 65-79 years Females Males Females Males Mortality ratios____........__- 2.17 7. 84 11. 76 11. 59 Death rates_.._.-..---- 22-2 e 2(7)15 | 2 (11)87 | 2(17)30] 2 (23)262 1 Computed from app. table 19. 2 Numbers in parentheses indicate death rate for nonsmokers. Sourcr: Hammond, E. C. (tables 24 and 26, app. table 19 (40). Tables 2 and 3 below show the relationships of number of cigarettes smoked per day, degree of inhalation, and age smoking began, to lung cancer mortality ratios and death rates for males and females, respectively. Generally, mortality ratios and death rates increase with increasing amount of cigarettes smoked and degree of inhalation, and with a longer lifetime history of smoking. Table 3 shows the relatively lower lung cancer mortality among women as contrasted to men, but reveals, for the most part, the same relationship to amount smoked, degree of inhalation, and age when smoking began. Table 4 illustrates the fact that cessation of cigarette smoking is associated with a decline in lung cancer death rates. * The mortality ratio is the ratio of the death rate of smokers to that of non- smokers—the mortality ratio of nonsmokers always being one, by definition. 134 TABLE 2. —Lung cancer (men). Number of deaths, and age-standardized death rates and mortality ratios, by current number of cigarettes smoked per day, degree of inhalation, and age began smoking, by age at start of study * Age 35-54 Age 55-60 Age 70-84 All ages, 35-84 Number of cigarettes a day, degree of inhalation, and age began smoking Num- | Death | Num- | Death | Num- | Death | Num- Death ber of | rate | berof| rate | berof] rate { ber of | rate deaths deaths deaths deaths Current number of cigarettes a day: 9 38 12 ci] 5 134 26 56 15 4 &7 168 10 23 82 90 138 88 216 204 27 446 381 159 26 47 50 334 6 754 82 201 Degree of jnhalation: None or slight... -----.----------- 19 2 87 203 4 193 120 102 114 52 17 224 20 401 311 138 Deop-..------------0-------2---- 55 55 3 206 13 63s wi 178 Age began cigarette smoking: 25 or older. 5 7 12 65 3 85 20 30 20 to 24... 31 36 72 212 7 306 110 118 15 to 19.-.- 112 4 176 250 2 490 318 155 Less than 15. 35 n 87 302 9 424 101 183 Never smoked regularly. i 6 a 10 u 25 49 12 Lung cancer mortality ratios (men) Current number of cigarettes a day: 1 tO 9.-- 2 nnn n ee een ne nen nne en nee eee 6.17 |.....--- 3. 53 5.32 4.60 10 to 19. - -- 3.90 -| 8.77 9. 62 7.48 20 to 30._...---.-------- +--+ --- | ---- => 9.37 -| 13.82 -| 17.62 13.14 40 plus ....---.------------------]----2 2° 7.67 |_.---.-- 17.47 }..------ 20.84 |..----.. 16. 61 Degree of inhalation: None or slight. 4.75 |.------- 10, 60 }..------ 7.65 |-------- 8,42 Moderate_....--- 8.48 -| 11.72 15.88 11.45 Deep.....----------------------- 9.00 13.93 25.26 j_.----- 14.31 Age began cigarette smoking: 25 or older. 2.77 3.39 j-.------ 3.38 |-------- 3.21 20 to 4... 11.11 ~} 12,11 J-_.----- 9.72 15 to 19._--..--..------ 13. 06 19.37 -| 12.81 Less than 15...---.------------ 15.81 {--..---- 16.76 |..-.-.-- 15.10 1 Mortality ratios are based on death rates carried out to 1 more significant figure than shown. Source: Hammond, E. C. {table 20 (40)]. 271-394 O—67——10 185 TABLE 3.—Lung cancer (women). Number of deaths, age-standardized death rates, and mortality ratios, by type of smoking (lifetime history), current number of cigarettes smoked per day, degree of inhalation, and age began smoking, by age at start of study } Age 40-54 Age 55-74 All ages, 40-74 Type of smoking (lifetime history) Number | Death | Number| Death | Number/ Death of rate of rate ot rate deaths deaths deaths 25 4 77 12 102 7 48 u 3 23 81 16 Current regular cigarette smoking 15 8 5 7 20 8 2B 7 2 50 50 35 16 13 9 18 2 13 7 i 18 48 45 2 7 6 16 21 23 2 35 14 i 43 46 7 Lung cancer mortality ratios (women) Never smoked regularly... 1.00 |-......... 1.00 [.......--. 1.00 History of cigarette smokin: 2.82 jee. 1.08 [.......... 2.20 Current regular cigarette smoking 2.08 [-....----. 0.62 |.---...... 1.06 4.43 |. 2222. 4.91 |..-..-.-.. 4% 3.33 1.12 178 2.90 4.04 3.70 1.55 1% 1.70 3.78 3.60 3.65 1 Mortality ratios are based on death rates carried out to 1 more significant figure than shown. Source: Hammond, E. C. [table 23 (40)]. 186 TABLE 4. tality ratios for ex-cig only, by former numb last cigarette smoking. Death a history of cigarette smoking only. Men are shown for comparison. Men aged 50-69. —Lwung cancer (men). Age-standardized death rates and mor- arette smokers with a history of cigarette smoking er of cigarettes smoked per day, and years since rates for current cigarette smokers with who never smoked regularly Smoked 1-19 cigarettes aday | Smoked 20+ cigarettesaday Mortality ratio, cigarette smokers (years eee last cigarette smoking) Number | Number| Death | Number | Number Death | 1-19 2+ of men | ofdeaths} rate | of men | of deaths rate 7468 3 108 2, 244 3 487 |_.--.---|-------- 1,844 5 cc") 5, 435 33 190 |......--|-------- 1,770 1 15 5, 803 22 108 |__..-.--|-------- 4,209 1 6 8, 142 5 16 j.---.---|-------- Total ex-smokers. -..-- 8, 569 10 30 21, 624 8 119 12.0 7.9 Current cigarette smokers...) 22, 808 80 97 56, 886 351 205 6.5 13.7 Never smoked regularly--..- 55, 728 32 15 55, 728 32 15 }..------|-------- 1 Computed from source. Source: Hammond, E. C. [table 21 (40). The Dorn study (49) of U.S. veterans provides additional informa- tion on the relationship of dosage to mortality ratios and death rates for males who smoked cigarettes only (table 5). TABLE 5.—Lung cancer mortality ratios and death rates for U.S. veterans by age, type, and amount of smoking Number of cigarettes/day 0 19 10-20 21-39 40+- pr'| mri |pR| MR |DR| MR |DR/} MR | DR; MR Current cigarette smokers only: Age 45 to $4_....---..----|------|--------|---2--| eee eee 24 52 72 |._.----- Age 55 to @4.___....-----. 10 1.00 70 7.00} 123 | 12.30! 206) 20.501 338 33.80 Age 65 to 74.._.--...----- 30 1.00} 135 4,50 | 265 8.83] 432 | 14.40] 696 23.20 Age 75 plus. 1.00 |-...-- Total. ---....-----.---- 1.00 j.--.-. 5.49 9.91 17,41 23.93 Ex-cigarette smokers only...-|.-----|--------]------ 95 248 9.33 |_..... 8. 24 1 DR, Death rate; MR, Mortality ratio. Source: U.S. veterans study [app. table A (49)]. 187 The mortality ratios of the Dorn (49) study can be compared with those of the Canadian veterans study, in table 6: TaBLe 6.—Lung cancer mortality ratios for Canadian veterans by age, type, and amount of smoking Number of cigarettes/day 0 | 1-9 10-20 214 Current cigarette smokers only: Age 30 to 49... 22-2 1. 00 2. 47 4.15 4. 08 Age 50 to 69__._--_----- ee 1. 00 10. 71 26. 92 26. 83 Age 70 plus____-_.__---...----.-_- 100] 12.15 9. 43 24, 53 Total__..---2 ee 1 00 10. 00 16. 41 17. 31 Ex-cigarette smokers only total_.____.__- 6. 06 Source: Canadian Pensioners study [(8), Table 8.1 and 8.2]. From the data shown in table 2 mortality ratios of 17.47 and 29.84 may be noted for smokers of 40+ cigarettes per day, age 55-69 and 70-84, respectively. The Dorn (49) study (see table 5) similarly shows mortality ratios of 33.80 and 23.20 for smokers of 40+ cigarettes per day, age 55-64 and 65-74, respectively. The Canadian study (see table 6) shows mortality ratios of 26.83 and 24.53 for smokers 50-69 and 70 years of age and older respectively who smoked over 20 cigarettes per day. There is rather close agreement among the three large prospec- tive studies for the general range of mortality ratios observed in heavy smokers. From the data supplied by the Doll and Hill survey of British physicians (28, 29) a mortality ratio of 31.86 can be calcu- lated for all smokers of more than 25 cigarettes per day, as com- pared to a mortality ratio of approximately 8, for smokers of 1-14 cigarettes per day (see table 8). There is relatively little risk of lung cancer associated with pipe or cigar smoking, probably because smoke from these sources is rarely inhaled. “Mixed smokers,” i.e., smokers of cigarettes, pipes, and/or cigars, have less risk than do smokers of cigarettes only, also suggest- ing that they may smoke fewer cigarettes or inhale less tobacco smoke than do smokers of cigarettes only (see tables 7 and 8). 138 TABLE 7.—Lung cancer mortality ratios by type and amount smoked Current smokers of cigarettes only pipe andjor Exemokers of Allamounts 1-9 10-20 21-39 40+ nipe and{o ¥ per day 12. 14 5, 49 9. 91 17, 41 23, 93 1 67 5. 00 Source: U.S. veterans study (app. table A (49)]. TABLE 8.—Lung cancer death rates by type of smoker and amount smoked Cigarette smokers An —| Given up | Mima | Pipe or Nonsmokers | SMoKets |, mounts| 1-14 | 15-24 | 25+ | smoking per day : 7 71 120 57 129 223 24 52 43 Source: Study of British physicians [tables 23 and 24 (28)). Taste 9.—Lung cancer death rates for ex-smokers of cigarettes by length of time stopped smoking Continuing Ex-amokers cigarette Nonsmokers smokers Less than 5 years 5-9 years 10-19 years 20-+- years 128 67 49 18 19 7 SouRcE: Study of British Physicians {table 25 (28)}. The preceding studies show appreciably lower mortality ratios and death rates from lung cancer with the cessation of cigarette smoking (see tables 4, 5, 6, 7, 8, 9). This lower risk is evident irrespective of the quantity of cigarettes formerly smoked. The Doll and Hill study (28) of British physicians is of particular interest in respect to ex-smokers. Over the 10-year period of the study (1951-61) 29 percent of the smokers of cigarettes only, had signifi- cantly decreased (one-half pack cigarettes or more) their smoking (in- cluding those who stopped) and 5 percent had switched to pipes and/or cigars. While the overall lung cancer mortality of men over age 25 in England and Wales had increased 22 percent over this 10-year period, that for the physician group decreased 7 percent. Since the total physician group is involved in these figures, we can compare this population group to the entire population of England and Wales where there was no general decrease in amount of smoking. This can be thought of as a controlled cessation experiment and the beneficial 139 effects of stopping or decreasing the amount of smoking become quite evident. Wicken (102), in a retrospective study of lung cancer mortality in Northern Ireland during the period 1960-62, reported the following results (Table 10) : . TaBLE 10.—Lung cancer mortality ratios and death rates, by sex, age 36 and over, by type and amount of smoking, Northern Ireland, 1960-62 Cigarette smokers Non- amount per day Cigarettes | Pipe and smokers and pipe | cigar only and cigar 1-10 11-22 | 238+ Male: Mortality ratios_.______ 1,00 | 483 | 9.33 | 21.2 5, 22 2.27 Death rates_._._.__.___ 18 87; 168) 383 94 41 Female: Mortality ratios. _._____ 1.00 | 2.27) 6 72) 19.0 ].-_-.._}L Death rates..___-_______ 11 25 74 | 210 |... ote SouxcE: Wicken, A. J. ((108), Table 17). Wicken also analyzed the proportion of lung cancer deaths which would have occurred if the lung cancer mortality rates of the least susceptible groups had been applied to the whole population of North- ern Ireland, and found that. males would have had only 18 percent of the lung cancer mortality if none smoked and that if they lived in truly rural areas they would have only 10 percent of the mortality. Thus, the difference—8 percent—may be attributable to the urban or suburban residence factor, possibly air pollution. If no females smoked, they would have had only 65 percent of the total female lung cancer mortality, and 53 percent if they lived in truly rural areas. Thus, for females, the difference of 12 percentage points might be attributed to the urban environment. The magnitude of these differ- ences depends on the prevalence of lung cancer in the various sub- groups of the particular population studied. Hisroparuoiocy or Lune Tumors Classification of lung cancer by histologic type was discussed in the Surgeon General’s 1964 Report with the conclusion that the squamous, undifferentiated, and oat-cell carcinomas were far more frequently found in smokers than in nonsmokers, while adenocarcinoma was rela- tively more frequent in nonsmokers, especially women. Changes in the bronchial mucosa resulting from the inhalation of cigarette smoke in- cluded loss of cilia, basal cell hyperplasia, and the appearance of atypical cells with irregular hyperchromatic nuclei. These changes, it was concluded, were related to the premalignant process of the de- 140 velopment of invasive carcinoma. Auerbach (6) has more recently reported on a study of the pathology of the tracheobronchial trees of 339 men who died from causes other than lung cancer and of 63 men who died from lung cancer. Up to 55 cross-sections of the tracheo- bronchial tissue were studied in each case. The 389 non-lung cancer cases included 65 men who had never smoked cigarettes and 274 men who had smoked in various amount. Figure 3 shows that only 1.38 percent of the slides from those who never smoked regularly have 60 percent or more atypical cells, whereas 76 percent of the slides of those smoking more than two packs a day had 60 percent or more atypical cells. (See figs. 3 and 4). PERCENT OF SLIDES WITH LESIONS SHOWING 60% OR MORE ATYPICAL CELLS 92.1 76.8 34.9 3.4 4.7 3 cCm71 1 Never Smoked 6 24 211 Adenocarcinoma. ..---------------------- 2 1 56 source: Ashley, D. J. B., et al. [(/) Table 4.] Insufficient information is provided in this study to specify in detail the past smoking histories, but the data suggest that cigarette smoking may be related to adenocarcinoma in some instances. . The preceding studies indicate that squamous, undifferentiated, and oat-cell carcinoma rarely occur in nonsmokers. However, it appears that cigarette smoking may also be associated with alveolar cell car- cinoma and glandular carcinoma of the bronchi. This relationship has been previously suspected. In fact as early as 1950 Wynder and Gra- ham (105) demonstrated this relationship. This was also shown in the study by Haenszel (39). Greater standardization and precision of diag- noses are needed to establish how few cases of undifferentiated or squa- mous carcinoma occur in nonsmokers who have been established to have never smoked appreciable amounts during their lifetimes. If 100 per- cent accurate smoking histories were obtainable on every case of lung cancer, it is suspected that very few cases of undifferentiated or squa- mous cancer would be found in persons who had never smoked. A report (98) on lung cancer in uranium miners noted a frequency of lung cancer, occurring almost entirely in the cigarette-smoking miners, greater than the frequency to be expected in a similar sized cigarette-smoking nonuranium mining population. A recent report (85) on bronchogenic carcinoma in asbestos workers also noted an in- creased frequency of lung cancer, occurring entirely in the cigarette smoking asbestos workers. This frequency was greater than the fre- quency to be expected for a similar population of cigarette smokers who were not asbestos workers. These reports suggest that cigarette smoking may interact with certain other environmental exposures to increase the frequency of lung cancer occurrence still further. Analysis of occupation and other environmental exposures must be performed simultaneously to detect which interactions with smoking seem to be especially dangerous. 148 EXPERIMENTAL PutmMonary CARCINOGENESIS Experimental attempts to produce lung cancer involve the admin- istration of tobacco smoke condensates and of carcinogens known to be present in tobacco smoke, either in vitro to preparations of cells or im vivo in experimental animals. Difficulties are encountered with the viability of tissue cultures and experimental animals when subjected to these various substances. Studies of human tissue from lung cancer patients indicate that abnormalities of the tracheobronchial mucosa, such as loss of cilia, basal cell hyperplasia, squamous metaplasia, and cellular atypism are important in the pathogenesis of human lung cancer caused by smoking. These changes have been experimentally produced in dogs exposed to cigarette smoke through a tracheostomy (2, 79, 80). A large number of dogs is now being studied to determine if lung cancer can be experimentally produced by this technique; if the dogs continue to smoke for a longer time, malignant changes may ap- pear subsequent to the already noted premalignant changes. The squa- mous metaplasia involved in the premalignant changes may explain why cigarette smoke condensate most readily produces cancer in the squamous epithelium of the skin of laboratory animals. AppitionaL Evipence ConcerNING EXPERIMENTAL CARCINOGENESIS The inhalation of tobacco smoke by mice was reported to increase the frequency of glandular tumors (37, 41, 63, 70). Syrian hamsters exposed to cigarette smoke developed a small number of tumors in the tracheobronchial epithelium (30, 1/0). Cigarette smoke condensate has been studied in tissue culture preparations (38), and implantation of cigarette smoke condensate exposed lung tissue subcutaneously has been reported to cause malignant growths (26). Cigarette smoke con- densate also causes skin tumors when applied topically (9, 11, 46, 48, 61, 74, 82, 107, 108). This was confirmed by a large-scale study with about 8,000 mice by the Tobacco Industry Research Council of England (22). Repeated injections of cigarette smoke condensate in rats produced sarcomas (32, 82, 83, 84). Since 1963 two studies have reported nega- — tive results when cigarette smoke condensate was administered intra- tracheally to rats and Syrian hamsters (25, 42) , respectively. Bronchoscopic painting of cigarette smoke condensate rapidly causes squamous metaplasia in dogs and may accelerate carcinogenesis (91). Carcinogens, known to be present in tobacco smoke, have been applied to cells in tissue culture with the observation of malignant changes (7) and other effects (22), such as differential growth inhibition of normal but not malignant cells (2%). Inhalation (53, 78, 90), intratracheal administration (25, 36, 42, 54, 81), subcutaneous, intraperitoneal and intravenous injection, oral administration, and skin painting of car- cinogens have all induced pulmonary tumors (87). 144 The search continues for an experimental animal system in which the inhalation of tobacco smoke will produce malignant tissue changes closely approximating those observed in human pulmonary cancer. When dealing with passive inhalation of tobacco smoke, however, a problem of the defensive barrier of the nasal passage is introduced. So far, dogs inhaling cigarette smoke through tra- cheostomies seem to be the most promising system, but there are problems in keeping the experiments going for the length of time nec- essary for lung cancer to develop. Additional research is needed. using cultured lung tissue together with autograft and homograft studies to determine in vivo results. Additional insight may thus be gained into in vivo systems. It should be noted, however, that it may not be possible ever to achieve histologic identity in pulmonary cancer production, not only because of difficulties in duplication of man’s smoking action for reasons of anatomic and physiologic differences, but also because of inherent species’ differences in cellular response. CANCER OF THE BUCCAL CAVITY AND PHARYNX (LIP, MOUTH, THROAT) The Surgeon General’s 1964 Report concluded that the causal re- lationship of pipe smoking to the development of cancer of the lip appeared to be established. Although there were suggestions of a relationship between cancer of other specific sites of the oral cavity and the several forms of tobacco use, their causal implications could not be stated at that time. The National Center for Health Statistics (94) reports that during 1964, 28 female and 157 male deaths occurred from cancer of the lip. During the period 1950-64, male mortality from this disease declined about 67 percent. This was partially due to changes in the diagnostic classification but was mainly due to increased early diagnosis and therapy. During the period 1958-64 when the seventh revision of the International Classification of Diseases was in use, total mortality from cancer of the lip remained about the same, but when analyzed by age, substantial decreases occurred in this death rate for each 10- year age group from 55-84 years. As for cancer of the oral cavity, other than the lip, the total death rate showed no marked variation from 1950-64 (3.1 and 3.3 deaths per 100,000 population, respectively). In 1964, the death rate for cancer of these sites in the male population was about three times the cor- responding rate in the female population (5.1 and 1.6 deaths per 100,000 population, respectively). 145 Morratrry Data From tae Larce Prosrecrive Sruprs Hammond (40) has reported data for males having cancer of the buccal cavity or pharynx, as the underlying cause of death, by mor- tality ratio and age-standardized death rates (table 12). TABLE 12.—Buccal cavity and pharyngeal cancer mortality ratios and death rates for male smokers, by type and specified age groups Cigarettes Pipe and/or Males Males Males 45-04 years 65-79 years 55-84 years Mortality ratio. _-__...--.--_____. . 9. 90 2. 93 4,94 Death rates____.-....22-- 222 +e 1(1) 8 '(7) 20 1(3) 15 ' Numbers in parentheses indicate death rates of persons who had never smoked cigarettes regularly. Source: Hammond, E. C. (40). The Dorn study (49) also has provided information with relation to amount and type of smoking on males dying from cancer of the buccal cavity and pharynx (table 13) : TaBLEe 13.—Buccal cavity and pharyngeal cancer mortality ratios and death rates for U.S. veterans, by age, type, and amount of smoking Current smokers of cigarettes only Pi Cigars Pipe Number of cigarettes per day and/or| only | only cigars 0 1-9 10-20 | 21-39 | 40+ Buccal Cavity: Mortality ratio....-......--.-.-. 10 0.86 2.93 7. 34 5.73 3. 89 4.11 3.12 Death rates: Age 45 to 54__ - 2B 97 Age 55 to 64__. 222 2 3 6 12 9 5 3 2 Age 65 to 74. _. 222-22 2-8. 4 fee 10 19 9 15 18 u Age 75 plus. -- 12