Document 7omgD9p92amonaMV2a7jXo3a

FILE NAME: Smoking (SMOK) DATE: 1953 DOC#: SMOK026 DOCUMENT DESCRIPTION: Book Excerpt - The Causation of Cancer - Further Considerations RECENT ADVANCES IN PATHOLOGY SIXTH EDITION By Various Authors Edited by GEOFFREY ^ADFIELD M .D., F.R.C.P. S ir W illiam Collins P rofessor of P athology, R oyal College of Surgeons of England W ith 86 Illustrations THE BLAKISTON New York 1953 COMPANY L u d fo r d , R. J., and B arlow, II. 1945. Cancer Research, 5, 257. MacCallum , W. G. 1903. Bull. Johns Hopk. Hosp., 14, 105. P arsons, R. J., and K id d , J. G. 1936. Proc. Soc. Exp. Biol, and Med., 35, 441. P arsons, R. J., and K id d , J. G. 1943. J. Exp. Med., 77, 233. P a sse y , R . D ., D m ochow ski, L ., R e e d , R ., a n d A s t b u r y , W. T . 1950. Biochimica el Biophysica Acta, 4, 391. P o r t e r , K. R., and T hom pson, H. P. 1948. J. Exp. Med., 88, 15. P d llin o er, B. I). 1949. Lancet, ii, 823. P u llin g er , B. D. 1952. Brit. J. Cancer, 6, 69. Research Conference on Cancer. A.A.A.S. for Advancement of Science, 1945. Washington, D.C. Rous, P. 1911. J. Exp. Med., 13, 397. Rous, P., and K id d , J. G. 1938. J. Exp. Med., 67, 399. Rous, P., Mu rph y , J. B., and T y tler, W. H. 1912. J.A .M .A ., 58, 1840. R u ssell, B. G. R. 1910. J. Path. Bad., 14, 344. Se l b ie , F. R. 1946. Brit. J. Exp. Path., 27, 143. Sh o p e , R. E. 1935. Proc. Soc. Exp. Biol, and Med., 32, 830. Sm ith, W. E., and Rous, P. 1945. J. Exp. Med., 81, 621. " A Symposium on Mammary Tumors in Mice." 1945. Washington, D.C. " Les Ultravirus des Maladies Animales." 1943. Paris. W oglom, W. H. 1913. " The Study of Experimental Cancer," New York. CHAPTER VII TH E CAUSATION OF CANCER : FU R TH ER CONSIDERATIONS SOCIAL AND RACIAL FACTORS IN CANCER T he influence of hygiene, occupational environment and social status on the incidence of cancer has been the subject of a fas cinating series of papers by Kennaway and his co-workers (1947, 1948, 1949). C ancer of th e L ung. This disease has increased sixteenfold from 1921 to 1945 in males (in England and Wales), whereas cancer of the larynx showed little change. In attem pting to explain this great increase of lung cancer Kennaway came to the conclusion th a t " although the incidence of lung cancer on those occupations where tlnSre is exposure to road dust (bearing in mind tarred roads) . . ." is rather, above the general level, it .seems very questionable whether the recent increase in this disease among the general population can be attributed to the tarring of roads. For scores of years before this increase began coal-tar was being discharged into the atm o sphere in the form of soot by the domestic fire in quantities vastly greater than any " th a t could now be derived from roads. Tarring of roads has undoubtedly increased the amount of dust derived from ta r in the air, but this increase appears negligible in comparison w ith the amount of soot already present." " Cotton mule-spinners show an especially small liability to cancer of the lung, althohgh they inhale air sprayed with an oil which produces cancer of the skin." " The high m ortality from cancer of the lung in towns (Stock), the low m ortality in agricultural occupations, and the absence of social gradient (Stevenson) are compatible with an etiological factor in the air such as coal smoke." Kennaway (1947a) is led to conclude th at " coal smoke does not account well for any recent increase in cancer of the lung." " One m ust look, therefore, for some other factors to explain th e increase, if there is a real increase, in cancer of the lung in recent years. Many such factors have been suggested, e.g. influenza, tobacco, popular drugs, tarred, roads, exhaust gases and other emanations, including lead ethyl, motor vehicles 143 222 VOSEASEIS OF THE LUNG Pneum oconiosis due to Silicates 1 Fibrous Silicates : Asbestos, Talc. The question as to whether silicates are toxic when inhaled has been very much debated since Jones (1933) p u t forward the view th a t sericite, a potassium alum inium silicate, is the cause of m uch industrial silicosis. Of recent years, however, his view has received very little support. Certain silicates are noxious, and the chief of these is the group of fibrous mineral silicates known as asbestos. There are two views regarding the mode of development of asbestosis. According to the one, the action of the dust is chemical ; the other view supposes th a t the asbestos fibres act mechanically. Experiments carried out a t the Saranac labora tories (Trudeau A nnual R eport, 1948) do not support the chemical theory, since aluminium hydroxide which neutralizes the toxic action of quartz does not prevent asbestosis. Moreover, asbestos fibres shorter th an 20p, were found to be relatively innocuous, whereas if the action were chemical an increase in potency would have been expected with reduction in particle size below 5p,, as in the case of silica. A comparison of the effect of asbestos fibres 15fj, long w ith those 2-5/x long (King et al., 1946) showed th a t rabbits receiving the long fibres developed a nodular reticulin formation comparable with experimental silicotic nodules ; animals receiving the short fibres developed a diffuse interstitial reticulin formation. The localization of the asbestos lesions appeared to depend oh the size of the fibres ; w ith long fibres, too big for removal by phagocytes, the reaction resulted in the formation of connective tissue within the alveoli ; with shorter fibres capable of being taken into the alveolar walls there was diffuse interstitial fibrosis. These workers suggest th a t if the fibres were shorter than 2-5^ they would be completely removed from the alveolar walls and fail to produce fibrosis. Johnstone (1948) concluded from clinical investigation th a t workers exposed to high concentrations of extremely fine asbestos dust did not suffer from asbestosis. The Saranac workers conclude th at asbestosis is caused by mechanical irritatio n from the asbestos fibres during the movements of respiration, and th a t this peculiarity is related to the flexibility of the fibres not possessed by other foreign bodies. -The view th a t movement of the lungs is a factor is supported by the absence of reaction to asbestos in organs other than the lung (Gardner, 1938). W yers (1949) points out th a t if the fibrous character is absent, as in the case ASBESTOS, TALC AND OTHER SILICATES 223 of serpentine, the chemical equivalent of asbestos, the dust is inert. The association of carcinoma with asbestosis has been mentioned above, b u t more details m ay be given here. An analysis of 235 cases of asbestosis is given in th e 1947 report of the B ritish Chief Inspector of Factories. Cancer of the lung or pleura occurred in 31 (13-2 per cent., average age 52-1 years). These figures were contrasted with the m uch lower incidence of cancer of the lung in 6,884 cases of silicosis, of whom 1-32 per cent, had carcinoma (average age 59-4 years). A high incidence of tuberculosis was also associated with asbestosis, and the Inspector of Factories found 72 instances in 130 cases of asbestosis. Talc. Numerous cases of pneumoconiosis due to talc (hydrated magnesium silicate) have been described in different parts of the world, and the first of this type in Britain, proved by autopsy, was reported in 1949 (McLaughlin et al.). Throughout the lungs there were grey nodules which had coalesced in some places, especially in the lower lobes. Microscopically the nodules showed whorling, b u t this had not the typical appearance of silicosis. W ithin the nodules were fibre-like structures up to 40j. in length arranged singly and in clumps. Some were very similar to asbestos bodies, and the appearances suggested th at talc pneumoconiosis and asbestosis are similar diseases and th a t the former m ay be caused only by th e fibrous varieties of talc. Asbestos is more actively fibrogenic th an talc, and this might be due to the higher proportion of fibres in asbestos. In New York State disabling pneumoconiosis occurred in 14-5 per cent, of the workers in the talc mining and milling industry (Siegal et al., 1943). The dust contained fine, straight, needle-like fibres. The talc fibrosis was associated with an increased susceptibility to tuberculosis. Glahs W ool. Glass in the form of fine fibres is being used in increasing quantities for heat insulation, and during its preparation and use the atmosphere m ay shimmer as a result of floating fibres. No harm appears to result, however, from exposure to this dust, since the fibres do not rem ain suspended in appreciable concen tration owing to the high electrostatic charge on them. Gardner (1942) considers th a t th e m aterial has not the properties required to produce fibrosis. N o n -fib rou s S ilic a te s : F u ller's Earth ; M ica. F uller's earth, composed m ainly of a silicate of aluminium, is found in Surrey, where if is quarried, dried and crushed. Middleton (1940j has given an account of the radiological and pathological changes