Document jgDn1LjLz88YqEkgdL27V4pv9

t.'.ie.i ri,if +. fcturtVUl. 284 27 March 1980 'Twrr'rr 297 f --,' T- ! S-.\:W. -1] - _______ .* BDistorSMg the epidemiology of cancer:. " T-v> j.% ror a morer UiS JL1 TvC i JQ overview *??.& r' 5^;Tne pOiitl:s of cancer are becoming increasingly polarised with V|</:;'>nviron:ncr.talists taking one extreme view and industrialists the T other. Richard Peto argues that a more dispassionate and ft Jisin:e*ested approach is required for a realistic assessment both Jio-i ;he risks from environmental carcinogens and of the s preventative regulations needed -------- :-------- -------------------- ` * hexe exist, botr. ia the general the consumers of their products, their , .ravircnment and i;i certain occupations, immediate response has usually been to :icnical or physical agents which increase delay acceptance of the findings, to V rae likelihood of human cancer. Our minimise their relevance to current t; political rcsocruc to this would, in an ideal practice, and in general to delay or obstruct Si**>ar:d vert -ciflciwLt knowledge was any hygienic measures which will cost ^ \iilat !t. . *ner.rt o;: the direct and indirect money. Even when human danger has been <vT; tjMs o: ui.: /.kriau* possible measures of unequivocally demonstrated, industrial ?j?foc:;c4 me jn r.ow many cancers each : consortia may actively lobby for controls m^ijurv would prevent. In the real so weak that (as with the new UK unimases of the direct finandal government regulations limiting inhaled p*' nr ths control of particular agents can asbestos to 1 fibre/ml from 1981) they w*.;' differ by one or two orders of leave no reasonable safety margin. Large i' r-ijr.itude, the indirect costs may be amounts of money are available to mount :* grossly exaggerated, or some major press or TV publicity campaigns about the v;. '.flairec; costs may be completely homely apple-pie virtues of asbestos, y cwtooked. Worst of all, we have in journals financed by the tobacco industry .4; ptisrai no remotely reliable estimates of run populist articles which misrepresent the numbers of cancers which particular research results to lay readers,' and some legislative controls would prevent. US television journalists are explicit!* told Consequently, there is wide scope for always to ce or all refer *ce w * (be "K ; pressure groups to have considerable dangers of smoKing. influence on public policy, Even the scientific literature is not historically, the most powerful pressure immune from distortion by financial ji- gray?* in US society have been the large interests. The decades-long argument that jJv foweia] interests, which have aimost "threshold" dose levels of carcinogens tfwr/s put financial advantage before must exist below which the general '-V bumu health. Over the past few years the population is absolutely safe has not been major tobacco companies have launched entirely motivated by the scientific swaivc sales drives ia the Third World, plausibility of the hypothesis. With ..Tdch if successful will kill millions of increasing understanding of the derivation : people. (About one in four regular of tumours from single cells acted on by .1 .airette smokers is killed prematurely by mutagenic carcinogens, industry is slowly .^noting.) In the US, where cigarettes abandoning "threshold" arguments in .*sas well over 100,000 deaths every year favour of arguments1*2 (where the fora lung cancer or chronic obstructive biological fallacies1*4 arc somewhat better disease, the tobacco industry refuses concealed by the mathematics) that u :c;u in public that cigarettes cause thousandfold reductions in dose can ..{ dil.jr disease, let alone to collaborate in ' conveniently be "statistically guaranteed" :,, t.` UT,c`jS public information, and no epithet to produce a million-fold or some other s-itabiy describe the collective efforts enormous reduction in risk. .-r .oftheir advertisers. Even if the scientists who propound suejg _ No other industry kills people on models are disinterested, industrial . K the scale that the tobacco endorsement of them ij not. Much . >-;'fllu,IfV does, but where other industries excellent toxicology may be done by ^tbcea found to cause cancer (or dust* industry, and many industrial scientists 'T` usiuced lung disease) in their workers or in and managers may be directly and honestly \l S' is a readtr in cancer studies at the ; -i 0/ Oxford. This article developed '? jT'.*' rrvievf of Samuel Epstein's book. The ^Xtr-fCnncer concerned with the prevention of hazards. But so many examples of financiallymotivated bias exist that the motives and WrtfV nf ! n r411 f p > a 1 (piamitt, consultants are inevitably distrusted. t4 Over the past quarter century', Uve AAmenerviciraonnmsoecniettay lihsats" camp In North pressed for (and achieved) stricter control of particular carcinogens in the work-place, the general environment, and the diet. Usually, their efforts have been directly resisted by the relevant financial interests. Inevitably, in view of the scantiness of reliable quantitative knowledge about the cancer* risks to man of nearly all carcinogens, the argument has polarised. In the politics of cancer, each side takes a very extreme position. Industry usually argues for the irrelevance to man of animal or in vitro cancer tests, or minimisies the quantitative hazards and exaggerates the costs of control. The environmentalists usually exaggerate the likely hazards and are largely indifferent to the costs of controL `The most powerful pressure groups in the US have been the large financial interests which have almost always put financial advantage before human health* The vacuum of reliable scientific know ledge is such that each side can find scientists who will maintain in courts, in public hearings orin thesrientific literature whatever is politically convea' it, and it is important to recognise that scientists on both sides of this debate now have career, interests at stake in it. A particularly good example of the biased writings of politically active environmentalists is Samuel Epstein's 77ie Politics of Cancer (Sierra Club Books, 1978, revised in Anchor Press, 1979). Epstein outlines, for university-educated but not necessarily science-educated readers, his view of our present state of knowledge about prevention of death from cancer. He concludes that the cure rates for the major cancers have not been improving much over recent years, but that we do know enough now about the causes of cancer for the testing and regulation of environmental contaminants to prevent the majority of US cancer deaths, and that the main obstacles to our doing so are political rather than scientific. He therefore reviews the scientific and *'5f>: * ."T 198 .ture Vol. 284 27 March IHo dozen or so disputed consumer products or occupational tuiards, providing much fascinating political detail, and then describes at length the internal politics of the various agencies which research, regulate and litigate in Washington. Epstein's book has been written to inflame political passions against environmental carcinogens, and parts of it -''are well worth reading. However, the political punch is often achieved at the ) expense of scientific accuracy and balance. ) Despite this, the book has already gained wide and apparently uncritical acceptance --even among scientists. For that reason, it is worth considering some of the misrepresentations of scientific evidence which it contains, and some of the more general defects in the environmentalist perspective on cancer. First, a few details, Epstein's book is very useful as a source of reference to original papers, but it is not in itself a reliable secondary reference because the material pr^nrA i rt Sometip^~~^ ^ CfreCtroTEPStein'j vigorous campaigning style on his scientific judgement and is, perhaps, t'orgivap^; at other it appears to be deliberate, which cannot so easily'bd tdfgiven. \ "-Tot example, consider the (by now generally agreed) finding that incor poration of about 57# by weight of saccharin into rat diets gives a few rats bladder cancer, but has no generally accepted effects on any other type of cancer. By human standards, S7o repre sents a vast saccharin intake (and so, of course, the industrial "Calorie Control Council" have tried to shrug off these findings). To refute the eomxnon reaction that "anything given in large enough doses will cause cancer in animals", Epstein's chief argument is to report that 0.017# saccharin has also been shown to be carcinogenic. In support of this extra ordinary claim, he presents in tabular form the control and 0.017# data for selected cancers from certain multi-group feeding experiments, leaving out the observations from those same experiments which would have refuted it (see table). This appears to- be a deliberate attempt to deceive the reader, (t is not a casual slip in a 600-page book, as Epstein devotes twenty pages and two full-page tables to saccharin. His entire table 6.4, entitled ` 'Tumours other than the bladder in rodents fed saccharin", appears to be so subject to artefacts of selection that it provides no evidence that saccharin does cause any rodent tumours other than in the rat bladder. Saccharin is not an isolated example of bias; indeed, I found that in many places where he discussed data with which I was familiar inaccuracies were present, almost always in the direction of accentuating the need for battle with the devils of industry. Turning to more important matters, Epstein asserts that any benefits from the "less dangerous" cigarettes which the tobacco industry has developed will be outweighed by people increasing their consumption to get more nicotine, and he is therefore in many places particularly scathing about (oreven downright opposed to) research into changed cigarette composition. This is a distorted perspective on one of the more promising immediate means of preventing fatal cancers, a quarter of which in America are currently due to smoking. Smokers of "less dangerous" cigarettes have already been found in various epidemiological studies to have disease rates which are materially lower than smokers of other cigarettes4*7; at autopsy they have far fewer "pre-malignant" histological changes in their bronchi* and, perhaps due to the changes in cigarette composition 10 or 20 years ago male lung cancer death rates in early middle age are now decreasing in t^orth America, in Britain and in Finland. After lung, the next commonest fatal cancers in the US are those of the breast and the large intestine, for which the most striking epidemiological finding to date is a 907# correlation between fat consumption in different countries and their breast or colon cancer rates (see figure; similar correlations exist for colon cancer*9). Epstein suggests that dietary fat -may Table: Data from OTA report* on the tumour sites selected for presentation in Epstein's book to substantiate the claim that O.Ot 7* saccharin is carcinogenic. Groups selectively omitted in Epstein's book are marked with an asterisk. Theseomissionssubstantially alter theimplicationsof theoriginal data. Saccharin dose (ft in rat diet; these doses have no material effect on longevity) 0 (control) -04)1 . 7 0.1 0.3 -71 ; s - Male or female ' lymphosarcomas (FDA, 1948) 1 0/20'(0ft) - . 8/14 (57ft) 5/16(3lft)" 2/15 (13ft)* 1/18 (6ft)* 10/17 (S9ft> Female breast (FDA, 1973) 6/26 (23 ft) . 14/30 (47ft) 13/34_(38ft)" 12/30 (40ft)* 12/17 (44ft)" *1 Male breast (FDA, 1973) 6/29 (2lft) 14/25 (56ft) . 9/27 (33ft)" -- 8/27 (30ft)" 7/25 (28ft)" Omitted in Epstein's book. In addition to these 20, since some other sweeteners were being tested concurrently, 34 other control animals were studied in the same experiment, and the 1977 OTA review of these data, considering all the eontrol animals to be equivalent, eited 9/54 control lymphosarcomas. (0/10 saccharin controls of each sex were studied, not ^'*10 as Epstein indvert y indicated.) CQU4#14/10/1KM not "Scientists on both sides of the environmentalist ; ; debate now have career ` . t- interests at stake' > merely be acting as a vehicle forfat-johicle pesticides and industrial chemicalsrVhii ' predictably emerge as his villains yetagaia. However, his suggestion is implausible countries with high levels of contamination do not stand out from the general cancer/fat relationship, colorectal ud breast cancer were common long before the widespread use of pesticides, and in experimental animals high-fat or low-fa diets can greatly enhance or reduce the risk of cancer11. Something more interesting is waiting to be discovered in our diet thaa simple contamination by carcinogens. The fat-associated and smoking-derivd cancers collectively account for more thu half of all cancer deaths, and people concerned with cancer politics should tzyto understand them considerably more accurately than Epstein appears to. One can list many other instances where Epstein's content or style are misleading or unbalanced. For example: The discussion of alcoholism and caacq is entirely erroneous because of failure to standardise properly for age. One of Epstein's chapters ends; "Eisenhower warned against the growing national threat of the military-industrial complex. The medical-industrial compla now appears to be as serious a threat". There is idealisation of the value oflong term animal tests with concomitant denigration of the value of the Ames test and other short-term tests. This is one of Epstein's most inexplicable erron of scientific judgement, unless be wants cancer tests to be difficult and expeasin for industry. He is irritatingly puritanical, sneering at "the plastic age which symbolises how tie value of our lifestyle has been degraded". He seeks by stylistic tricks to attribute w oral contraceptives some ofthe established hazards of hormone replacement therapy and of diethylstilboestrol. He claims that cancer costs the US economy over S25 billion per year. (In fact, cancer must be prevented for humane, mi for economic reasons; without cancer, there would be three or four million more retired North Americans to support, costing over $26 billion per year). And so on. He seems so certain about everything -- how can anybody bejustified in hcuinsoccruifl IbOUrRrmany^ttaih? SometimesJ know he's wrong," out more often (cspeciaUvm,LtKeTHanrqfctCCT>wher incondusive saenfIc~results-igm'esMri as established fac~t)_l knovr-thet-nobodT knows for sure, Lewis Thomas onic wrote, in another' conccxt:~"Thc sceptics s meJione have a hard.UffJSjSfit. itismui more difficult to ' ignorance concerning disease mechanism 1a V--M V '.**N*, .f-JV uuj 7v mrg ickE n m n ri ic 'i _ilun it is to ;r.akc claims for full .comprehension, especially when the comprehension leads, logically or not, (o c od additives. Indeed, one of the most ii. .guing animal findings is the effect in many studies of gross aspects of diet on `Pre it day cancer rates and trends are probably ' joe sort of action. When it comes to : serious illness, the public tends, understandably, to be more sceptical about the sceptics, more willing to believe the true cancer; for example, mice randomised between 5g of food once daily and ad lib consumption averagin g 6g/day of the same food, had respectively S9b and not dominated by 'r: occupational carcinogens or environmental * ..SLi?v*t 4*.rI believers." spontaneous mammary turn out , and tfte pollutants* Epstein (like many others) is role of dietary fat11 has already been unjustifiably definite about three major discussed. issues. He seems certain that even after the Thirdly, Epstein seems certain that at both of whom still seem more ready to ; effects of cigarettes have been allowed for, least a quarter of all cancer deaths are defend than to repudiate it. { Americans live in an era of rapidly attributable to occupational exposure to Entitled "Estimates of the fraction of ' increasing cancer rates. But trends in carcinogens. There is as vet no good cancer in the US related to occupational j "recorded cancer death rates tana, perhaps evidence for hazards of anything like this factors", it shows how a roua of < 'more <o_ rgenrdfri ino^enee rarest over the magnitude, and there is clear evidence that reasonable men can collectively generate a! oast quarter century are biased upwards many of his particular claims, are an unreasonable report. The group (since the gjfft nfg ! improvements in medical care and cancer exaggerated. For example, he says that as&estos has led to approximately 50,000 deaths per year in the US from cancer and multiplied the li milusjrtfbrKers exposed in any way in 1972-4 to any ofasbestos. As, Ni. Cr, benzene or petrochemicals by the .^counting. These improvements have related disease (referencing a paper by very large risk factors (e.g. fivefold lung iWhe NCI-NIEHS report Selikoff1* which actually neither makes nor * cancer excesses) typical of much more implies any such claim). This is sheer extensively exposed industrial populations, ;/shows liow a group of 1I reasonable men can . collectively generate ah ^unreasonable report* 53------------------------------------------------------------^affected all sectors of US society, but most nonsense; of 50,000 asbestos deaths, several thousand should be certified as being due to pleural mesothelioma, yet only several hundred per year are thus certified. Likewise, Epstein cites with approval (indeed, he describes it as being of "epochal significance") Health, finally multiplying again by "4-5" to allow for the additional cancers that will be caused by these six agents among workers exposed to them at times other than 1972-4. (In casual disregard of dosimetry, this ,, , whole process is very like predicting 100.000 occupational lung cancer deaths, per year among non-smokers due to their aj / ' J ' L; ^particularly old people and previously poor Education and Welfare Secretary exposure to other people's dgareue smoke ^people, especially blacks. Epstein, along Califano's absurd 1978 estimate, in a at work, "since 209b of heavy smokers get itviLh most other uS commentators, does t^aoi allow for these biases even to the Baited extent of restricting his attention to speech to labour union leaden, that as many as half of the 8-11 million workers who have been exposed to asbestos could lung cancer"). These assumptions "predict" over .''-'A.''C .-drV 200.000 extra respiratory tract cancers per ^trends in age-specific mortality rates develop serious diseases such as cancer or year in the near future due to the above six tfsmong middle-aged whites, where they . asbestosis. In his second edition, Epstein agents alone (and are the sole source of the h eight be expected to be least prominent. draws extensively on Califano's source, a* currently widespread prediction of Among middle-aged whites during the curious but extremely influential document "20-389#" of cancers being due to Typist quarter century, cancercure rates have which has been circulating privately for the occupation). But, in reality, fewer than i*aot materially improved, but some US past year or more. This unpublished 90.000 males/year get respiratory tract 7-oncer mortality trends seem to be typescript, with no listed authors, was cancer in the US (and most of these are due ft genuinely down (stomach, cervix) while prepared by a working group of nine well- to cigarettes and not to occupation at all), ;`jome seem to be genuinely up (pancreas, known scientists including Arthur Upton and moreover the US male rates in the first t'melanoroa, and certain lymphomas). I can and David Rail, the National Cancer 25 years of working life are currently ^`discern no net pattern other than that due Institute and National Institute of decreasing! A prediction of 100-200,000 f'.tb the massive effects of smoking on lung Environmental Health Sciences directors. extras due to the above six agents is clearly } f cancer, although no extension to 1978 yet ly exists of the excellent 1950-67 trend Figure: data9 plotting for 39 countries age-versus total dietary fat (animal or fir*WJiTfd breast ti analyses in NCI monograph 33. In Britain, cancer death rate vegetable). ..." - r* the same is true12.as long as we examine mortality in middle age. (Interestingly, {' although Epstein emphasises that bladder | cancer death rates among whites in the j' industrial north-eastern US are high, this i; may not be chiefly due to any current r*.industrial hazard, for they have been ft decreasing both relatively and absolutely *r for a quarter of a century12.) |jT Epstein also seems certain that the ' 25 20 IS Female KCTHeoLOPOS *uK aoewAAK Caf**-"* sew ZLfiLAK) .aoSsWmEDaENua' *J5T*N+*O*wr moNca- CTEO i 1 v ^..majority of human cancer is caused by ^/chemical and physical agents in the >. avironment and could be prevented by ;' their testing and regulation. There is no | sound scientific basis for this certainty, t. Since the cancers (lung, breast, large r intestine) which are commonest in the US IV5 4 10 *3 M < eo(*Tuoa. rKjKAttr K5%o*o*o ecLOPO Cx vENCz!uet(-*-aV* .SPUN scwa>A ''VGO^aya ->*eC mpaico ****** & t ve rare in certain other countries, and v/ce [ ww, they probably really are preventable, ThAH-IONO ElSa^v. e .bui (see figure) not necessarily by ;u MJ 60 SO 100 120 140 160 ISO f1 regulation ofany environmental pollutants Total dietary fat intake (f/day) t r _>xot:wwiu942ui.co OtMOMaoUluJmfMli Ud rr vaturt Vol. 28* 27 .Wen ` r. J -very unrealistic. .ath rates'2 should be more widely more iflan the equivalent amount o( 3Z TVs unreality of the whole method is known. dietary saccharin would have done11). further highlighted by the fact that the My criticisms Of Epstein's science, Also, any chemical which causes prolife, "assumptions ''predict" 7,300x4.5 nickel- however, must be viewed in the light of the ation or necrosis in any organ that is' -Toxide induced occupational lung cancers/ continued resistance of many industries to subject to spontaneous cancers is likely to year. Since nickel refining causes a lot of reasonable controls. One has only to read modify the onset rate of rumours in that * nasal as well as lung cancer, we would some of bis descriptions of industrial organ, and since the aim of most animal 1 presumably then also soon "expect" behaviour to see where his passion comes experiments is to study a dose which it < something like 13,000 nasal cancer death from, and a suitably sceptical reader could nearly, but not quite, sufficient to cause . certificates per year among nickel workers. derive much important information from significant weight loss or mortality within Nickel has already been widely used for the dozen or so detailed case-histories of three months, it is not surprising that so .' decades, so many thousands of these particular carcinogens that make up the many chemicals at such doses can cans: /should presumably already be evident. In bulk of this book. But, although 1 cannon cancer in animals. v*; .''reality, each year in the US population prove it, 1 suspect that environments^ft However, itmaybethalwhereadversay : there are only 300-add male and ZOO-odd a whole (including lspstcin and Those US politics operate one needs views at both / female nasal cancer death certificates. The a.n<T"Br'itijh':ra3eunTons'wHrc'h~haYe extremes in order to get a balanced out- *; majority of these are not ex-nickel workers - alrdy"mo<fiIfrd^he:(j)u'blic^staiemeflts come. And there is a possibility that over- .`.'and no marked trends are evident. This v demonstrates the unsoundaess of the NCI--- fiNlEHS methodology, ;' "?...... "3 ' Unfortunately, meh exaggerated closely'oif'fiis book) would _be better `The politics of cancer is V emphasis on the avoidance of scientific ierror would emasculate the environmental- j ist passions and merely lead to my own' rather inactive conservatism. (After aH.oo estimates are so much what_manv people dominated on both sides scruples about scientific certainty ofsafer/ //Srisr- 7. wanllo believe ot modern society that they f, hsCVeTfoVachlevedTlire oFfrieir own, and. by exaggeration* usually precede the widespread introduc- C allhougli*ntHey~*are'"-utTiiiyIlZwiCiout -I: fodWaitfon thcy__are quotcd^yidely. respected and could^thereforejpress more * repeatedly andjepuu^ 'cffect[vcIy"for corTfrojs'ln..particular Environmentalists with biased judge / antf^Vcientiflc^press. In Geneva the instaiiccs iV thclTovcrvicw of cancer was ments and a quasireligious certainty of vrSfeTnatiorial Labour Organisation more balanced! in'tHe'iSlfowmg.ways: right will fight more battles than uy~:T. ^ 'freportedly endorsed them, as did the Toxic - Tf they'acceptetTtha present-day cancer reasonable sceptic .would do, and even if . .'^Substances Strategy Committee in their rates and trends are probably not their victories confer 10 or 100 times less T * recent draft report to the US president14, , dominated by occupational carcinogens or . benefit on humanity than they Imagine, 3? and they have been used in OSHA to environmental pollutants (especially since they will in the long run probably do more VA'/t; '/emphasise the need for stricter laws. Most they could still warn that future rates might good than harm -- unless they materially !;recently, the UK trade union the perhaps be so nominated unless present- reduce food production, distort research Association of Scientific, Technical a. . day expc -esai regulated20); priorities, or direct attention away from the , Managerial Staffs (ASTMS) released a policy if their chief concern' was with the smoking problem in the process. Epstein { document which appears to have been V strongly influenced by Epstein's book, and which is notable for its prominent but identification and control ofthe few major determinants of human cancer (or, in an industrial context, the few major industrial justly quotes, from the I st century AD, the Plutarch chronicles: "He who in time of faction takes neither side shall be disco- erroneous assertion, derived solely from carcinogens) rather than the large frachised". So, I feel, should both environ- the foregoing unpublished US typescript, multitude ofsins which Epstein denounces; mentalists and industrialists who suppress y . that 20-40of current UK cancer deaths if they discussed the costs and benefits of or deliberately misinterpret data, but they are caused by occupational carcinogens. research into the control of toxic probably won't be. For the moment, the t / Epstein now claims that these substances in the context of other possible 'politics of cancer* is dominated on both . .> -^exaggerated estimates seriously ways of improving longevity (bad diet and sidesbyexaggeradon. *.J,nQ ^underestimate the impaet of industrial tobacco in rich countries, malnutrition and ` v carcinogens. There is obviously a valid / political need to exaggerate theimportance infective and parasitic diseases elsewhere); if they took the costs of imposing ------------------------------------;--------- !- ' of the preventive measures we can already restrictions on society more seriously. Epstein's general assertion is that the total I. CoraTM..;.*wcrltt.V3<IVTT). `For most toxic chemicals we now have both qualitative and quantitative uncertainty about the health benefits 'of restriction*. implement, but in the tong run we do also still need to discover the main preventable causes of cancer other than smoking. - direct and indirect costs of failing to regulate usually exceed the real costs of the testing and regulation, but I suspect that this is a slogan to avoid political embarrassment rather than a carefully researched conclusion; if they accepted that for most toxic chemicals we have.both qualitative and vast quantitative uncertainty about the health benefits of restriction. -Particularly, even if the son of grossly biased interpretation which Epstein applied to the animal saccharin data is avoided, the results of animal experiments U79|l*#l. j. lira 4. Guau. W.A.iiat Camr /tarvthJ7, J47J (lT7>, m! ''3. J. Orrwa of TdiftO(ofy AufUfltou of ift US Ceoc ' <*. ( 1>77); flaw TaMt TtrhAoioff jW Str/Itrvr. f 4. Hammond. E.C. H af i* Ongitu ,/Wmw Ctnetr. CflU ' . t:.. -- Sprint Huber NY (1Vtt>. -. ?. Winder. E.U. <*< USfoianuMM OHEWpub&pM .ttV-.' NIH Tf-llll tl>74). I. Au*ibcfc.O.</WMr/nrfr.Aft J0*,MI(19T9|. 9. Cott.lt.UCa*rtrJ*fwrt IS. )J7*|I97J). 10. Ammrea|. B.kl. uid OoU, A. /HLj.C*^err\f. ! ?a'7.'V H. ;M O.C. StdUUtQA CttKir VJ). It (19T9). I Mur other papa, in all tlil9T9Utua oftAuiounuiireofpai fcnrral imtnu .|. tl3)-33, 47 and 17. Jn ii*o pvt 1 * Neva>bc ,197S Cmaf fnotk tenMt *Mlr vt muuueo and anett). II. OoU.fc.J^.Xo/.SocZ*AtajS.Tti9'TV>. 1). Slot. WJ. iad fuuwol. Coocw'/w t. 10H Bearing both these needs in mind, there are limits beyond which it is not even politically wise to distort the science of cancer, and some of today's exaggerations may well transgress those limits. Reliable reviews of the known and suspected eauses,1'i*-'* of human cancer and of trends in British simply are not an uncomplicated key to human hazard identification. First, moderate alteration of gross aspects of the diet of animals greatly modifies their spontaneous tumour onset rates" (so, for example, increasing the sugar content of rat diets may increase their cancer rates 1197IU 14. Ro. r j.C. nd Tockn. M l. ZikiryM Aftdko i.l- Coriiu Strta) ill. 171 (irr). 15. 3tikoff, l.J. in "Ontiuof KubmCumw", CoU Spn* Htrtw NY 11977). 14. Noimui, A. 114. it) < 1979). 17. OoU. X<Von.tr 1*5.119(1*77). kl. OoU. ft. Nvtru>* Ctmt IO>. IS (19791. 19. IA AC vorkiaf prove Ctww fiuorik 40.1 flSfO). . Dam. D.U ud Mbsot, B.H. Sn*nr 104. US4(t*79k OOU4IM/W/I))MI]SOI .00 l940MKiwaw JoumaltUd '