A British Medical Association Lecture ON THE EXPERIMENTAL INQUIRY INTO THE CAUSES OF CANCER

A. Leitch
1923 BMJ (Clinical Research Edition)  
Atn)v as arpec.ea pe'V LcraaL /.LoUvoi 6EOt, EOIKvtav ae Kat aVBpcolToL.-AiIETAEUS. WITH SO much kiiowni of the actual manifestations of tumour growths, anid wvith their antecedents so obscure, it is little wonider that speculation regardinig the causation of cancer has so lonig held its sterile and unprofitable way. The gossamer fanicies of the armchair philosopher nieed scarcely a breatlh of criticism for their destruction; and as for the theories of the greater thinkers, the outcome of
more » ... he outcome of miiuch experienice car efullv interpreted, we may for the pr'esent adopt the (dialectical strategy of Hegel and say that possibly they all represent partial and different aspects of the truth. Anxious as we should be, in view of the poverty of our knowledge, to avoid bound allegiance to any theory, we cannot wholly dispense with working hypotheses, and the recent experimental investigations have been born of the idea that can-cerous growth is the result of some lonig-continlued irritation. That is the oldest theory of them all. The ancient Greek )hysicians imagined that cancer, as well as many other diseases, was due to the irritatiing and acrid properties of the black bile. Are there not some to-day who attribute to intestinal stasis, a notion not less nebulous, a similar wide-embracinig r6le? Virchow, the father of modern pathology, contended that tumouirs were caused by irritation of a chemical or physical nature, not further defining or particularizing, for there had not then accumulated the imposing list of special agents that we now know to be closely associated with the production of cancer. His was a theory that anticipated the evidence. Probably we shall find-our experiments point that way-that few of the substances which we might call tissue irritants are capable of inducing tumour growth, just as out of the myriads of kinds of bacteria there are relatively few which are definitely pathogenic. These specific irritants, or carcinogenief agents, as far as we know them, require a proloniged time to work their effects, and they appear to be selective in that certain animal species, certain strains, certain individuals, anid certain tissues only are vulnerable to their operation. In the human subject we have the well known instances of the cancer of the scrotum to wlhich chimney-sweeps and labourers in the tar, pitch, and paraffin industries are specially prone; the cancer of the urinary bladder in dyeworkers and in the victims of bilharziasis; the epithelioma pmf the abdomen and thighs in natives of Kashmir; the multiple skin cancers in those who have taken arsenic * Delivered before the Nottingham Division of the British Medical Association, January 24th, 1923. f From icapvri'o, a tumour, simple or malignant, and veivao.. to produce. Such adjectives as cancrigenic, cancrogenic, and cancerigenic, which have bAen uked by others, are hybrids to be avoided. -Aj medicinally over long periods; and the epithelioma of the hands in x-ray operators. These and several others seem to show a very intimate relation between particular irritants and tumour formation, but several considerationis lhave long stood in the way of establishlinig a direct cauisal connexion betweeni them. Comparatively few of the subjects exp)osed to the action of soot, tar, paraffin, aniline dves, anid the rest develop malignant tumours; even those whlo become affected lhave been in contact with the noxious substances for maany years: more arresting still is the fact that several of these workers lave retired from such occupations and yet, years afterwards, lhave developed the same peculiarly localize(d cancers. Conisidering, too, the numerous inistances of maligniancy supervening on otlher chroniic lesions, alnd tlhe fact that the so-called irritationi cancers are so rare in comparison with the large numbers of tuliours arisinlg withlout tlhe intervention of any knowin or suspected irritanit, we lhave lhad to admit tllat our carcinogeniic agents miglht onily be the mediate and not thle proximate causal factors of the disease. All that we could claim for them was that they brought about a pathological state of the tissues, oni whiclh piepared soil the undetermined cancer germ or virtus or influence might then exert its action. Sometimes, however, the progression of events was so uininterrupted-as, for examiiple, in arsenic cancer, where skin hypertrophy merges into wart formation and w-arts insensibly into epithelioma-that it was difficult to point to any particular time when one factor could give l)lace to another. But no amount of argument could settle tlho matter. No one had ever produced canicer exporimeintally by the usO of any of the implicated irritants. Of course, nlumerous claimiis to have done so by the injection of this or that parasite lhave been put forward. Let us not resurrect them. The silenit records, too, of our laboratories contain many a failure that we have niot liked to parade. But a new era dawned on canicer research when Joliannes Fibiger of Copenhageni presenited his brilliant experiments on tlhe production of gastric cancer in rats. Then for the first time could it be said that cancer lhad been produiced experimentally beyond all doubt, and explorations into tlhe etiology of cancer became practical problems. SPIROPTERA CARCINOMA. While examining the bodies of three rats that hiad been inoculated witlh tuberele l)acilli Fibiger found in each case a cancer of the fundus of the stomach. Sutch a tlhing lind niever before been seen in time rat, thouighi soores of thousanids of these animals had been examinied for tfmniours. Malignianit new gr;owtlhs (lo exist in rats, abouit onee in a thousand cases, but canicer of tle stomiach had never beeni observed. Fibiger at once endeavoured to piropagate thle tumours b1 inioculationi of fragments inito othler irats, anid failed. Freslh rats were fed with otlier lpieces of tlhe tumour; niotllinig happenied. Aniothier batch was l)ut in tile cages previously occupied by the infected raits; they remained unaffected. Microscopic investigation(of tlhe gastric tumours sllow-ed thieni to be el)itlleliomata, for tile cardiac lhalf of the rat stomachl is lined with squtamous epithelium, and amonigst the PI)ithelial c(ll mass(s thlere were round spaces sometimes containing a peculiar structurie that suggested sectiolns of ani aniimal l)raasite. Tracing [3262]
doi:10.1136/bmj.2.3262.1 fatcat:ura7upgz2ndirmjzzwfmj5fj6q