INTRINSIC FACTORS in the ETIOLOGY of NEOPLASMS' It Is

INTRINSIC FACTORS IN THE ETIOLOGY OF NEOPLASMS'

CARL V. WELLER, MS., M.D. (From the Department of Pathology, University of Michigan) It is as true as it is trite that the cause of disease is never a single factor. Two elements always enter into etiology. One of these is inherent in the germ plasm of the individual; the other brought to bear upon the organism from beyond the confines of the germinal elements from which it has developed. Better than internal and external, endogenous and exogenous, or con- stitutional and environmental, to designate these two groups of factors, are the terms intrinsic and extrinsic. Practical experience directs us to seek the relative importance of intrinsic and extrinsic factors whenever the causation of disease is studied, and we find that the two ingredients may be combined in every possible proportion. At one end of the series are diseases such as deaf mutism, transmitted as a simple recessive, in which the intrinsic element almost crowds out all other considerations. In the recessively sex-linked hemophilia, again the intrinsic element is so prominent that we see at once the mendelian significance of the process, although the bleeder may not be made known until the extrinsic factor, trauma, opens his blood vessels. The asthenic, dolichomorphic bodily configuration, which marks the phthisical habitus, is a familial character and therefore intrinsic, but it conditions infection by the tubercle bacillus in such a way as to give it serious or even lethal possibilities. When we consider syphilis, we find that the Treponema is no respecter of genetic constitution, yet sex and race may modify the character of the disease. These four com- monplace illustrations are chosen advisedly to invite attention to a serial arrangement of diseases between those predominantly intrinsic and those predominantly extrinsic. Where in this series does neoplasia belong?

There are several destructively critical attitudes which seem to be incom- patible with an open-minded scientific approach to the question of intrinsic factors in the etiology of neoplasms. (1) The first of these is the assumption that intrinsic factors are not concerned in the causation of neoplasms, because, if they were, it would make popular education about cancer difficult. What other inference can be drawn from the statement, in a deservedly popular monograph on Neoplastic Dis- eases ( l), that the author subscribes to the conclusion : " Nothing authorizes us to affirm that cancer is hereditary; in the interests of the public this doctrine ought to be combated "? (2) The second conception which I believe to be largely fallacious is that information obtained from lower animals is of no value in the oncology of 1 Read in a Symposium on the Genesis of Tumors, American Association of Pathologists and Bacteriologists, Chicago, March 26, 1937. 39 40 CARL V. WELLER man, The problems of neoplasia are biological problems, and the processes of life are so fundamentally similar throughout the Vertebrata, and particularly in the Mammalia, that we cannot afford to disregard knowledge which comes from animal experimentation. That neoplasms of the lower animals and of man are as similar as they are should be occasion for rentark, and not otherwise. This similarity extends through gross and microscopic pathology, comparative age incidence, benignancy and malignancy, power of metastasis and mode of termination. (3) Again, the criticism is sometimes raised that familial incidence of benign neoplasms is of no significance in respect to the etiology of cancer. There are two reasons why this is not true. The first is that no sharp line of demarcation between benign and malignant new growths can be drawn; the second, that benign new growths, sometimes presenting a familial incidence, may furnish the essential preblastomatoid somatic alteration upon which cancer may appear. This seems to be the case with carcinoma developing upon intestinal polyposis, as may be illustrated by the family described by Barker (2). (4) It should be obvious that intrinsic factors are operating whether there be direct transmission of a predisposition to neoplasia or whether the inheritable condition is a somatic structural or functional variation which makes the affected individual more vulnerable to the cancerigenic effect of extrinsic factors. Neither a gene for " cancer " nor a " cancer-resisting " gene is essential for exemplification of intrinsic factors in the etiology of neoplasms. (5) Finally, a necessary change in the point of view of many must come with the realization that both proponents and opponents of intrinsic factors in the etiology of cancer have, in years gone by, limited their discussions too rigidly to questions of genes and of mendelism. Achievements with Droso- phila and Oenethera may have provided alluring vistas, but there is accumu- lating evidence that very broad conceptions of the transmission of certain qualities must be entertained. The specialists in the field of genetics are fully aware of this trend. I quote from Baur (3) : "We have likewise reason to expect that hereditary transmission in accordance with other laws than the mendelian will occur in the case of all social differences which are based, not upon peculiarities of the chromosomes, but on those of some other part of the idioplasm. Differences in the structure of the remainder of the thread equipment of the cell nucleus, in the structure of chromosomes, etc., must certainly produce differences in the finished organism. . . . Very numerous observations on plants combine to show that hereditary differences in their vitality are transmitted in accordance with other laws than the mendelian. . . . The mendefian laws of separation do not prevail universally, and . . . in the case of man no less than in that of other organisms, we are likely to encounter phenomena of hereditary transmission which do not occur in accordance with these laws." Marsh (4) recognized the importance of this broad view when he wrote in 1929: " One might infer from the discussions of cancer heredity in which dominance and re- cessiveness are set off against each other that cancer must belong to one or the other in inheritance. This would be to forget that dominance is no essential of the mendelian system and that both members of an allelomorphic pair may appear in F,." And MacDowell (5) has recently made a vigorous statement of this view: INTRINSIC FACTORS IN THE ETIOLOGY OF NEOPLASMS 41

" It is highly regrettable that, outside the immediate circle of geneticists, there seems to be an impression that the gene is self-sufficient and is either dominant or recessive. Espe- cially as applied to neoplasia this misunderstanding has led to erroneous conclusions both on the part of hostile critics and ardent believers. Dominance is only a special case at the end of a continuous series of interrelations between pairs of genes. No gene can produce its effect without cooperation of many other genes. . . . And genes and extrinsic conditions co- operate in all cases."

CLINICALEVIDENCE FOR AND AGAINSTINTRINSIC FACTORS IN THE ETIOLOGYOF NEOPLASMS From the clinical side there are several classes of evidence for and against the significance of intrinsic factors. From each of these only illustrative samples can receive specific reference. (1) Cancer Families: The occurrence of several cancers in the same family attracts both lay and medical attention. Since approximately one-tenth of the population dies of cancer, the operation of the laws of chance should give some families with no cancer at all and others with an excess of cancer. It is doubtful if the basic data are as yet available by which to determine through statistical methods the degree of familial concentration which is mathematically significant of transmitted predisposition. Yet, practical experience gives at least a temporary answer, and the general opinion is that there are families in which the mass incidence of cancer is significantly in excess of the normal expectation. More than a hundred such families can be collected from the world's literature, but many such reports lose part of their value in that often only affected individuals are indicated. Perhaps the most thoroughly studied cancer family is that twice reported by Dr. Warthin and recently brought up to date by Hauser and myself (6). Of 174 members of this family attaining an age of twenty-five years, 41 developed 43 malignant neoplasms. Of even greater importance than the total number of malignant neoplasms are the facts (1) that in some branches of this family cancer has never occurred, and (2) that with two exceptions all cancers in the family have been of the gastro- intestinal tract and uterus. Twenty males have shown cancer, all of the gastro-intestinal tract. It is expecting too much of chance distribution that 20 men with gastro-intestinal cancer should be found in one family without a single example of cancer of the lips, tongue, mouth, esophagus, bronchus, or penis. The only example of a squamous-cell carcinoma in this large family was a small lesion of a woman's nose, treated successfully by local eradication. (2) Family History of Cancer Patients: The family histories of large groups of cancer patients should be of value in determining whether effects of intrinsic factors are revealed through heredity. Evidence from this source is somewhat contradictory. Hunter (7) reviewed family histories from the insurance application blanks of those who subsequently died of cancer, in comparison with those of insured persons dying from other conditions. He found that there was no significant difference between the two groups. If anything, those dying of non-cancerous conditions were somewhat more apt to have given cancer as a cause of death of parents or siblings than were those who had died of cancer. Lack of accurate knowledge of causes of death of ancestors, reluctance to admit deaths from cancer, and preponderance of males among the insured, are obvious difficulties in a study conducted in this manner. 42 CARL V. WELLER

Deelman (8) utilized questionnaires, with a non-cancer case of the same sex and age balanced against each case of cancer. He found cancer to be more than twice as frequent among the parents, and three times as frequent among the siblings, of cancerous individuals as in the families of the non- cancerous. This excess of cancer in the families of cancer patients, however, was accumulated by comparatively few families. With these " cancer families " eliminated, there was left a large group of cancer patients in whose families cancer was absolutely not more frequent than agrees with the " normal " chance of dying of cancer. The most elaborate investigation of this nature, particularly in its mathe- matical treatment of the data, was that of Waaler (9). He obtained 6,000 schedules, the starting point of each of which was a cancer patient. A corps of 115 specially instructed medical students collected data on the cancer history of parents, spouse, children, and siblings of each patient. -4s to spouses, he found that no excess cancer mortality over the general population existed. The incidence of cancer was significantly greater among the sisters of cancer patients than among the wives of the patients or in the general population. Among males, the difference was considered inconclusive. Waaler's figures show that the proportional cancer mortality in the siblings varies with cancer incidence in the parental generation. When one or the other parent had cancer, the proportions for male and female sibs were 40.7 and 53.8 per cent. When both parents died at ages over sixty years, of disease other than cancer, the corresponding figures were 21.7 and 23.1 per cent. The female sibs of patients with cancer of the breast, uterus, or ovaries showed a larger proportion of cancer than the male sibs, and the type of tumor from which the patient suffered was largely represented in her female sibs. For instance, cancer of the breast appeared in 44.7 per cent of the cancerous sibs of patients with cancer of the breast, and in but 16.5 per cent of the cancerous sibs of females with cancer other than that of the breast. However, no such relationship was found to exist when the siblings of males with cancer of the lip were considered. Cancer of the lip appeared to be distributed quite independently of inheritable Anlagen. Wassink (10) obtained results largely in accord with those of Waaler. He also found a marked surplus of similar malignancy in the female relatives of patients with cancer of the breast and uterus, while with cancer of the lip there was some, but much less strong, evidence of organ susceptibility. The female relatives of 660 patients with breast cancer yielded 112 cancers of the breast and 14 of the uterus. The female relatives of 403 patients with cancer of the uterus yielded 15 cancers of the breast and 29 of the uterus. (3) Multiple NeopEasms in the Same Patient: The incidence of multiple neoplasms in the same patient is much higher than was formerly believed. The question has been surveyed by Warren and Gates (ll), who conclude that multiple malignant tumors occur more frequently than can be explained on the basis of chance. My associate, Dr. Bugher (12), has computed from cancer mortality statistics the expected occurrence of coincidental multiple primary malignant neoplasms. After collecting our cases and those from the literature, he, also, found that the actual incidence must exceed that expected from chance alone. Inherent susceptibility is, of course, not the only possible INTRINSIC FACTORS IN THE ETIOLOGY OF NEOPLASMS 43 explanation of this excess, but at present it seems to be the most satisfactory one. (4) Familial Concentration of Particular Neoplasms: Medical literature is replete with examples of the familial occurrence of particular neoplasms, both benign and malignant. In this category are found nevi and neuro- fibromas of all types, the tumor acusticus, gliomas, retinoblastorna, carti- laginous exostoses, epithelioma adenoides cysticum, adenoma sebaceum, fibro- adenomas of the breast, uterine leiomyoma, cerebellar hemangioma (Lindau's disease), osteogenic sarcoma, choroidal sarcoma, leukemia, Hodgkin's disease, intestinal polyposis, xeroderma pigmentosum, complex teratomas, and carcinoma of the breast, uterus and gastro-intestinal tract. Some of these are of such rarity that the probability of two examples falling within the same family by chance alone is extremely small, as has been emphasized by Macklin (13). She notes, for example, that of 60 cases of retinal angioma recorded up to 1930, 6 were in one family and 3 each in two other families; yet not once has it been recorded in husband and wife. Special reference should be made to retinoblastoma because it affords strik- ing demonstrations of familial concentration, and because it is not generally known that there may be a vertical as well as a horizontal distribution of retinoblastoma in a family line. There are numerous examples of isolated retinoblastoma, but all are familiar with the tendency for this terrible neoplasm to appear in siblings. For instance, Newton (14) reported 10 of 16 children involved; Thompson (IS), 5 of 14; Wilson (16), 8 of 8. How significant this distribution is, is shown by the fact that retinoblastoma has an incidence of 0.01 per cent, not in the total population, but in those having diseases of the eyes-1 1 cases in 114,764 admissions according to Letchworth (17) ; 131 cases in 1,259,452 admissions according to Berrisford (18). There are now a considerable number of reports in the literature of persons who survived enucleation for retinoblastoma only years later to see their children or grandchildren afflicted. Berrisford (la), for instance, reports the case of Thomas G., who survived the enucleation of his left eye when five months old. From his son, Frank, one eye was removed at five months. There was no recurrence, but the child died of paralysis at fifteen years. (Survivors following enucleation for retinoblastoma seem to die with other neoplasms more frequently than chance distribution would explain.) Beatrice, a daugh- ter of Thomas G., was apparently normal, but of her eight children, three required bilateral and one unilateral exenteration for retinoblastorna. There are but two alternatives for a child with this neoplasm: exenteration, frequently bilateral, or death. Even though a majority of cases occur without retinoblastoma in the forbears, sterilization of those surviving exenteration would seem to be a wise and justifiable procedure. (5) Monochorial Twins: Since monochorial twins develop from a single ovum fertilized by a single spermatozoon, they should receive similar hereditary equipment; and the large number of uniovular twins in which neoplasms have been similar, simultaneous, and symmetrical is impressive. Such a list has been compiled recently by Militzer (19). When, first, the great variety of possible neoplasms is considered; secondly, the possible variations in ana- tomical site; and, in the third place, the possible extent in time, coincidence 44 CARL V. WELLER in all these respects, occurring in a considerable number of twins, must be determined by factors other than chance. The evidence here favors intrinsic factars. Versluys (20) not only collected case reports but also made a statistical study of unselected material. Of 32 pairs of monochorial twins with tumors, in 9 both partners bore tumors and in 23 only one. Of 35 pairs of dichorial twins, in 9 tumors occurred in both and in 26 in one only. Statis- tically approached, of 27 pairs of monochorial twins, both had tumors in 8 pairs, while in the remaining 19 pairs only one twin in each developed a neoplasm. Of 35 pairs of dichorial twins both had tumors in 12 instances, whereas only one twin of each of the other 23 pairs had a new growth. From these results Versluys came to the conclusion that hereditary influences have little or no effect in the causation of neoplasms. He found, however, that when both monochorial twins have tumors these are of the same type and involve the same or homologous organs. Thus hereditary factors seemed to determine the site. EXPERIMENTALEVIDENCE Experimental studies of intrinsic factors in the etiology of neoplasms fall into several fields, which can be touched upon but briefly. Tyzzer (21), in 1907, produced the first significant study of heredity in relation to the tumors of mice. Through his work and that of Loeb, Slye, Lathrop, Little and his associates, Strong, Lynch, Zavadskaia, and many others, it was established that high-cancer or low-cancer strains of mice could be developed by selective breeding, and that there was definite evidence of inheritable specificity in respect to tumor type and tumor site. It is a pleasure to pay tribute to the indefatigable perseverance of Dr. Slye, whose labors of more than twenty-five years, involving the breeding, recording, and autopsy of more than 125,000 mice, have made nearly a half-hundred scientific reports possible. In retrospect, it is not surprising that various workers came to different conclusions as to the mendelian implications of their results and as to the number of genes concerned. Strict mendelian ratios could not be obtained, for, as has been often said, cancer is not a permanent somatic character like coat color, determinable soon after birth. The action of extrinsic factors and death before the demonstration of neoplasia interfered. It became evi- dent that all cancer could not be considered together; and more precise methods with animals approaching chemical reagents in genetic purity are now the rule. The demonstration of an hereditary basis for melanotic tumors in hybrid fishes by Gordon (22) confirmed in another zoological class and for another neoplasm the importance of intrinsic factors. From another form of experimental attack has come evidence which promises to be extremely important. Murray and Little (23) have found by reciprocal crosses between cancerous and non-cancerous lines of mice that the tendency to produce mammary tumors of epithelial origin is transmitted largely by means of extrachromosomal influences, while some other neoplasms do not follow this law. Similarly, MacDowell (5) found for spontaneous leukemia in mice a difference in hybrid generations dependent upon whether INTRINSIC FACTORS IN THE ETIOLOGY OF NEOPLASMS 45 the leukemic heredity is transmitted by mothers or fathers. The incidence of spontaneous leukemia in the first hybrid generation was 19 per cent higher when the mother came from the leukemic strain; and in the back-cross, 26 per cent higher when the mother was the hybrid parent. Since the chromo somal mechanism was shared equally by fathers and mothers, the implication is clear that besides the familiar chromosome transmission, some extrachromo somal mechanism also is involved, and that this is probably cytoplasmic. The relationship between intrinsic and extrinsic factors in the etiology of neoplasms is being actively investigated in many laboratories. Reference may be made to the reports of Fekete and Green (24); Kreyberg (25); Zavadskaia and Garrido (26); Dunning, Curtis and Bullock (27); Andervont (28), and C. F. Branch (29), for type studies in this field. In general, this work has shown that intrinsic factors condition the response to extrinsic cancerigenic agents; but that the extrinsic factor, if sufficiently potent in its action, may induce malignancy in strains of animals ordinarily non-cancerous. In conclusion, I summarize my personal views in respect to the part which intrinsic factors play in the etiology of neoplasms, fully realizing that in the time available for this presentation, I have not been able to present supporting evidence for each point. ( 1) Since cell division and tissue growth are intrinsic attributes of every metazoan organism, every organism possesses the basic intrinsic factors es sential for neoplastic growth. (2) Neoplasms, like all other disease processes, result from the combined action of intrinsic and extrinsic factors. (3) If the extrinsic factor is sufficiently potent, it is conceivable that neoplasia may be induced in any organism. (4) In addition to this universal intrinsic attribute, the actual occurrence, the type, and the site of neoplasms is determined, in part by specific intrinsic factors, but to varying degrees and in different ways for different new growths. (5) There is no gene for "cancer" as a whole, or for "non-cancer." The significance of intrinsic factors, the part played by genes and by extra chromosomal factors, and the mendelian implications, if any, must be worked out separately for each kind of neoplasm. (6) In certain instances neoplasia develops upon morphological or func tional abnormalities which are themselves intrinsic and inheritable. Some . of these are dominant and some recessive in the mendelian sense, and the resulting neoplasms tend to approximate the hereditary pattern of the lesions upon which they develop. REFERENCES 1. EWING, JAMES: Neoplastic Diseases, W. B. Saunders Co., Philadelphia, 3d ed., 1928, p. 112. 2. BARKER, L. F.: Polyposis of the colon, Med. Clinics North America 14: 77, 1930. 3. BAUR, E., FISCHER, E., AND LENZ, F.: Human Heredity, translated by Eden and Cedar Paul, Macmillan Co., New York, 1931, pp. 93-94. 4. MARSH, M. C.: Spontaneous mammary cancer in mice, J. Cancer Research 13: 313, 1929. 5. MACDOWELL, E. C.: Genetic aspects of mouse leukemia, Am. J. Cancer 26: 85, 1936. 6. HAUSER, 1. ]., AND WELLER, C. V.: A further report on the cancer family of Warthin, Am. J. Cancer 27: 434, 1936. 46 CARL V. WELLER

7. HUNTER, ARTHUR: The inheritance of cancer in mankind, Am. J. Cancer 19: 79, 1933. 8. DEELMAN, H. T.: Heredity and cancer, Ann. Surg. 93: 30,1931. 9. WAALER, G. H. M.: Ueber die Erblichkeit des Krebses, Skrifter utgitt av Det Norske Videnskaps-Akademi i Oslo. 1. Mat.-Naturv. Klasse No.2, 1931. Abst. by M. Greenwood in Cancer Review 7: 464, 1932. 10. WASSINK, W. F.: Cancer et heredite, Genetica 17: 103, 1935. 11. WARREN, S., AND GATES, 0.: Multiple primary malignant tumors. A survey of the literature and a statistical study, Am. J. Cancer 16: 1358, 1932. 12. BUGHER, J. C.: The probability of the chance occurrence of multiple malignant neo plasms, Am. J. Cancer 21: 809, 1934. 13. MACKLIN, M. T.: Heredity in cancer, and its value as an aid in early diagnosis, Edin burgh M. J. 42: 49, 1935. 14. NEWTON, R. E.: Glioma of retina-a remarkable family history, Australasian M. Gaz. 21: 236, 1902. 15. THOMPSON, J. L.: Glioma of the retina, J. A. M. A. 31: 628, 1898. 16. WILSON, H.: Quoted by Clausen in Zentralbl. f. d. ges. Ophth. u. ihre Grenzgeb. 13: 32, 1924. 17. LETCHWORTH, T. W.: Four cases of glioma retinre in one family, Brit. Med. J. 2: 656, 1928. 18. BERRISFORD, P.O.: Statistical notes on glioma retinae, with a report on forty-one cases, Royal Lond. Ophth. Hosp. Reps. 20: 296, 1916. 19. MILITZER, R. E.: Carcinoma of the stomach in identical twins, Am. J. Cancer 25: 544, 1935. 20. VERSLUYS, J. J.: Zwillingspathologischer Beitrag zur Atiologie der Tumoren, Ztschr. f. Krebsforsch. 41: 239, 1934. 21. TYZZER, E. E.: A study of heredity in relation to the development of tumors in mice, J. M. Research 17 (n, s. 12): 199,1907-08. 22. GORDON, MYRON: Hereditary basis of melanosis in hybrid fishes, Am. J. Cancer 15: 1495, 1931. 23. MURRAY, W. S., AND LITTLE, C. C.: Extrachromosomal influence in relation to the inci dence of mammary and non-mammary tumors in mice, Am. J. Cancer 27: 516, 1936. 24. FEKETE, E., AND GREEN, C. V.: The influence of complete blockage of the nipple on the incidence and location of spontaneous mammary tumors in mice, Am. J. Cancer 27: 513, 1936. 25. KREYBERG, L.: On the genetic factor in the development of benign tar tumours in mice, Acta path. et microbiol. Scandinav. II: 174, 1934. 26. DOBROVOLSKAIA-ZAVADSKAIA, N., AND GARRIDO, F.. Existe-i-il des lignees du Souris refractaires au cancer du goudron, Compt rend Soc. de bioI. 122: 509, 1936. 27. DUNNING, W. F., CURTIS, M..R., AND BULLOCK, F. D.: The respective roles of heredity and somatic mutation in the origin of malignancy, Am. J. Cancer 28: 681, 1936. 28. ANDERVONT, H. B.: The production of dibenzarrthracene tumors in pure strain mice, Pub. Health Rep. 49: 620, 1934. Further studies on the production of dibenzan thracene tumors in pure strain and stock mice. Pub. Health Rep. 50: 1211, 1935. 29. BRANCH, C. F.: Dibenzanthracene tumors in controlled strains of mice, Am. J. Cancer 26: 110,1936.