Document 2qnkx63G8yEraB78k5KyJYLob

Pulmonary Tumors Induced in Mice by Vinyl Chloride Monomer1 Yasunosukf. Suzuki3 Environmental Sciences Laboratory, Department of Community Medicine, and Department of Pathology, Mount Sinai School of Medicine of the City University of New York, Fifth Avenue and lOOlli Street, New York. New York 10029 Received August 15, 1977 Neoplastic effects of vinyl chloride were studied in Jungs of 27 mice exposed to vinyl chloride monomer at 2500 and 6000 ppm for 5 and 6 months. Pulmonary tumors were observed in 26 of 27 experimental animals. By light microscopy, the tumors were multiple and ar ranged in either tubulo-papillary or adenomatous formations. Although occasional mitotic divisions and invaginations into the bronchiolar lumen were observed, no metastases were found. By electron microscopy, short microvilli, tight junctions between two adjacent cells, appearance of osmiophilic lamellar bodies, large mitochondria of irregular shape, welldeveloped Golgi complexes, continuous or discontinuous basement membranes, occasional appearance of "sequestration" and of crystalloids, and lack of both cilia and mucous secret ory granules were observed as characteristic features of the neoplastic cells. Some of the cells were poorly differentiated and were equipped with poorly developed organoids, with out formation of osmiophilic lamellar bodies. The pulmonary tumors corresponded to "alveologenic tumors or alveologenic cancer." It is suggested that the neoplastic cells were transformed from type IJ alveolar epithelium via its hyperplastic form. It is concluded that mouse lung is an extremely sensitive indicator of the oncogenicity of vinyl chloride. INTRODUCTION Hepatic hemangiosarcoma has been accepted as a serious health hazard as sociated with vinyl chloride exposure among workers in vinyl chloride polymeri zation plants (I -7). A risk of lung cancer has also been reported among the workers on the basis of epidemiological studies (8, 9). Experimental studies in rats, mice, and hamsters have shown that, in addition to liver, various organs such as lung, brain, breast, and skin, including sebaceous glands, were involved in induction of primary neoplasia by vinyl chloride. Al though a number of studies have demonstrated that pulmonary tumors can be induced by vinyl chloride in mice, the significance of such occurrence and the nature of the tumors have not yet been appropriately explored (10-18). We have undertaken a preliminary study of pulmonary oncogenetic effects of vinyl chloride in mice to provide information on these questions. A num ber of significant observations have been made: frequent occurrence of pul monary tumors, unique ultrastructure of the neoplastic cells, findings concerning the precursor of these cells, as well as data regarding the submicroscopic aspects 1 Supported by Center Grant ES 00928 from the National Institute of Environmental Health Sci ences. U.S. Department of Health. Education and Welfare. - To whom requests for reprints and correspondence should be sent: Environmental Science Laboratory. Mount Sinai School of Medicine, Fifth Avenue and 100th Street. New York, N. Y. 10029. 285 0013-9351/78/1613 - 0285S02.00/0 Cop> right i IV78 h\ Aciuictnic Prc-N Uw, All right-H of reprmJiictmn in jn> form rescrvi\J. 286 VASUN'OSLKF. St'/.fKI Fig. 1. Two pulmonary tumors induced by vinyl chloride are seen in the peripheral part of a mouse lung (2500 ppm in group 111). Hematoxylin and eosin: x 64. of the neoplastic transformation from the precursor cells. Details of these findings are reported here. MATERIALS AND METHODS Twenty-seven CD1 Charles River white strain male mice, 4 to 5 weeks old at first exposure, were used. These animals were divided into three groups. In group I, six animals were exposed to vinyl chloride at 2500 (three mice) and 6000 (three mice) ppm/hour, 5 hours/day, 5 days/week, for 5 months. They were then kept for 6 days without exposure before sacrifice. In group II, 13 mice were exposed at 2500 (seven mice) and 6000 (six mice) ppm for 6 months and were kept for an additional 2 days for recovery before sacrifice. In group III, eight animals (seven at 2500 ppm and one at 6000 ppm) were exposed to vinyl chloride monomer for 6 months followed by a 37-day recovery period. Thj: inhalalion^exoasures-were "accomplished at the Industrial Bio-Test Laboratory_N.orthbreokT-Ill. "Tiraddition to the "experimental animals, 16 mice (four for group I, four for group II, three for group III, and five which were 12 months old) were simultaneously maintained as controls. The control mice were primarily of interest for providing data concerning the spontaneous occurrence of pulmonary tumors. Under anesthesia, the mice of both experimental and control groups were sac rificed by decapitation. Lungs were examined under a dissecting microscope after the organs were taken out of the bodies to determine whether tumors had occurred. Fic. 2. A part neoplastic cells ar i For light mic malin and em micrometer sei silver, periodic tin, and Van ( pieces, smaller neoplastic puln | at pH 1.2-1 A j in epoxy resin sections were : croscope was t major organs, i hemangiosarco the hepatic effc A. Cross Atwti Pulmonary tt 6000-ppm serie tumors were ro; PULMONARY TUMORS INDlT.l.O RY VINYl. CHLOKIDL - ^ V*?- CVi1- % . * ^ 0 V ii.J , _ '** ; * . r> i ' > , v - ,X * X **'' e VI >*-** " he -' .--.St:, > **. ; UCl . -j * **#- v - *'#.. -.# 'crT]j*.*** cp-^ - . s,-^*5* .-v*5< vS >' & ,-v^P. '* 4sf?*. **.^*:> 4-.fi k-** pS** V.; .-*-- ^ '-* * %r f 287 ..%: v---.r Jb- Co>N/ Fig. 2. A part of the lower tumor seen in Fig. I. A tubulo--papillary pattern is observed. The neoplastic cells are basophilic. Hematoxylin and eosin: x 400. For light microscopy, the organs were fixed in 109 neutral buffered for malin and embedded in paraffin after dehydration in alcohol. Five- to sixmicrometer sections were made and stained with hematoxylin-eosin, Weigert's silver, periodic acid-Schiffs (PAS) with and without digestion by diastase, elastin, and Van Gieson's picrofuchsin technique. For electron microscopy small pieces, smaller than 1 mm3, were taken from both pulmonary tumors and non neoplastic pulmonary tissues and w ere fixed in 1% phosphate buffered osmic acid at pH 7.2-7.4 for 2 hours. After alcohol dehydration, the blocks W'ere embedded in epoxy resin, Ultrathin sections were obtained with an LKB microtome. The sections were stained with uranyl acetate and lead. A Siemens 101 electron mi croscope was used for ultrastructural observations. In addition to the lungs, other major organs, including the liver, were examined. To the present, three hepatic hemangiosarcomas were observed in the 2500-ppm series of group III. Details of the hepatic effects of vinyl chloride will be reported elsewhere (19). OBSERVATIONS 1. Gross Anatomical Findings Pulmonary tumors were observed in all experimental mice except one from the 6000-ppm series-of group II (26 of 27). None were found in lb controls. These tumors w'ere round, w'hitish in color, multiple in number, and variable in size from 288 vasunosuke si'Zuki Fig. 3. A part of the upper tumor seen in Fig. 1. An adenomatous pattern is seen. Hematoxylin and eosin; x 560. ! to to 5 mm in diameter. No metastases to regional lymph nodes or other organs were observed. Neither parenchymal fibrosis nor fibrotic adhesions of the pleura were detected. B. Light Microscopy As shown in Fig. 1, the tumors were usually seen in the peripheral part of lung parenchyma, although occasionally tumors were found in more proximal parts of the lung. No direct connections of the tumors with bronchi or bronchioles were observed. The neoplastic cells were arranged in various ways, such as tubulo-- papillary (Fig. 2) and adenomatous forms (Fig. 3). Polymorphism and atypical structures were not striking. However, sometimes abnormal mitoses were ob served, as shown in Fig. 4 (arrow labeled M). The nuclei were round in shape and small, and chromatin was generally finely distributed. Nucleoli were generally poor in development. Two different types, eosinophilic and basophilic, were dis tinguished in the neoplastic cells (Figs. 2 and 3). Some of the cells stained with PAS (Fig. 4; arrow), and the substance so stained was digested by diastase, suggesting that it was glycogen. The neoplastic tissue was not encapsulated by connective tissue. Often, air spaces separated neoplastic tissue from normal tis sue. Although malignant invasion, such as destruction of preexisting tissue, was not observed in the animal lungs, invagination of the neoplastic tissue into bron- Fic.. 4. Neor by diastase. Th chiolar air sj and reticular to neoplastic changes of tl In Fig. 5, the lining cells b be alveolar t cells. Hyper shown in Fi lobe of the h not always c dent identifi not feasible C. Electron Figure 7 i 2). Ultrastri round- or i miophilic la cent neopla ri l.MONAKY TUMORS INDICT l> HV VINYL CIII.OKIDi: 289 "v - L?Vi .* ~ n r>Jp-> *1 'it v\u-t&. TO -i ,*P. %-<C 3D v'Xtf'l >v r *6:5* -*v :%W. .V. iili Fi<;, 4. Neop!a>lic cells stained with PAS. An arrow indicates fine PAS-positive material digested hy diastase. The arrow labeled M shows an abnormal mitosis (2500 ppm in group III), x 560. .'hiolar air spaces was detected in instances of extremely large tumors. Collagen .tntl reticular fibers showed little development in the neoplastic tissues. In addition :o neoptastic changes, as shown in Figs. 5 and 6, focal and multiple hyperplastic changes of the alveolar lining cells were noted in lungs exposed to vinyl chloride, in Fig. 5, the hyperplastic cells are seen just beneath the visceral pleura. Since the ining cells beneath the thin connective tissue of the visceral pleura are known to be alveolar epithelium, the hyperplastic cells are assumed to be alveolar epithelial cells. Hyperplastic cells are also found in the deeper part of lung parenchyma, as 'hown in Fig. 6. Occasionally, neoplasia and hyperplasia coexisted in the same lobe of the lung, and the distinction between neoplastic and hyperplastic cells was not always clear, as some cellular similarities were found between the two. Confi dent identification of the cell types of both neoplastic and hyperplastic cells was not feasible at the level of light microscopy. ; . Electron Microscopy Figure 7 is derived from neoplastic tissue of the tubulo-papillary form (see Fig. Ultrastructural characteristics of the neoplastic cell included microvilli, large, ; >und- or rod-shaped mitochondria, well-developed Golgi complexes, and osi iiophilic lamellar bodies. Junctional structures (arrows in Fig. 7) between adja nt neoplastic cells and a basement membrane (B) were usually observed. Figure - 3fi?ftattWBrsrg^ 290 rfW^^frPrTirV' YASUNOSUKK SUZUKI gp-vf* ... '>>$ . ft A v-r Fic. 5. Hyperplastic pulmonary cells are seen beneath the visceral pleura of a mouse lung (2500 ppm in group III). Hematoxylin and eosin; x 430. > I. ' v * *V&>'*4 f--3* * V s rV -V -t 4 Zi* ' * /.w* .V% S .* v %y*.' .*? t, **^V 4..- Fir.. 6. Proliferated alveolar lining cells in the deeper part of lung parenchyma. (2500 ppm in group III). Hematoxylin and eosin; x 170. J--'--ifltf<iwni<*>fiinJii iwf-m(i PI * ',t ; v ,..,1 > < * vT* a.. -.vP'.'/J!: ^--J. - *.' v-w- . iV i>a O ^ 'yv;\. .&. ..^*.D;'_ *-r A. \ f '$. ^ $: JJph Fit;. 7. A low-pc junctional structure 7900. 8 was derived poorly formed: Fig. 7. Howev Golgi complex two. Irregular mitochondria v mic reticulum partments fort compartments scopic observr EC- 1348 I'L LMONAKV TL'MOkS INDLC.KI) 11V VIXV1. ClllOKlUt; 'xv'; ;i .--i **- ,~ 291 !H Ki\ ?''iSSsh?STS -S * " w C*- ; r-t'U *-- ,, 1f~x Jf. 1- *% - , . V,/i .* Fu;. 7, A low-power electron micrograph of a well-differentiated pulmonary tumor. Arrows indicate junctional structures between neoplastic cells. B. Basement membrane (2500 ppm in group III), x 7900. 8 was derived from an adenomatous area shown in Fig. 3. Neoplastic cells had poorly formed tubular lumens and microvilli and were smaller than those shown in Fig. 7. However, other ultrastructural characteristics, such as mitochondria, Golgi complexes, and osmiophilic lamellar bodies, were almost identical in the two. Irregular arrangements of cristae mitochondriales were fairly common, and mitochondria were often wrapped by well-developed smooth-surfaced endoplas mic reticulum (Fig. 9). Some of the neoplastic cells contained cytoplasmic com partments formed by membrane structures (Fig. 10). The occurrence of such compartments has been reported by Svoboda (20), who made electron micro scopic observations on the neoplastic cells in mouse pulmonary tumors induced 3 w'-i.. ft . I? II r 'n: , v v ^< `V "Ke-rS^si.i.3rr^zy 4: wssraasEsteES' :.l 1 34 e: . `M S -! <M s M 1 1349 292 VASL'NOSL'KF. SUZUKI Fig. 8. A differentiated neoplasm seen in the animal lung shown in Fig. 3. Formation of the tubular lumen and microvilli is poor, x 6500. spontaneously or by urethane. Intracytoplasmic vacuoles containing electrondense granules (diameter: approximately 400 A) and amorphous material were frequently observed in the cell cytoplasm (Fig. 11). Since the limiting membrane was attached to ribosomes, the vacuole was identified as a cisterna of endoplasmic reticulum. The intracisternal granules did not stain with uranyl acetate alone and therefore were assumed to be glycogen (Fig. 12). Occasionally, crystalloid struc tures were observed in the cytoplasm of the neoplastic cells (Fig. 13), though their significance has not been clarified. The above-described neoplastic cells were quite similar in ultrastructure to type II alveolar epithelium. Capillaries in the neoplastic tissue consisted of single layers of nonfenestrated endothelium as seen in the normal alveolar capillary. In addition to well-differentiated neoplastic cells, poorly differentiated ones were also recognized (Fig. 14). As seen in Fig. 14, the cells were cuboidal or cylindrical in shape and lacked formation of osmiophilic lamellar bodies. Mitochondria were small in size, although the cells were rela tively rich in rough-surfaced endoplasmic reticulum. These cells seemed to cor respond to the basophilic ones observed by light microscopy. Except for the lack of a large amount of glycogen, these cells resembled immature alveolar epithelium, as observed in fetal lung in late gestation. Neither cilia nor mucinous Fic. 9. A pa mitochondriales secretory gn it was strong epithelium, r illustrated ir were eviden ences in ulti size and inn miophilic lai chrondriales reticulum v. membrane i served in tht was derived type II cell i form betwe pulmonary ; which may 3" IMW)*W'Jwt^iWi>''JM^<iiaii ^iw.lJij{gr^r-l-.!r-TT:,,;v^:/_7^:V-v.^' I'ri.MOXAKV IUMOKS INDlCtO MV VINYL f HI.ORIDL 3 293 Fig. 9. A part of the cell cytoplasm of a neoplastic cell- The arrow indicates irregular cristae mitochondriales (2500 ppm in group III), x 29,400. secretory granules were observed in the neoplastic cells. Based on these findings, it was strongly suggested that the neoplastic cells were derived from the alveolar epithelium, particularly from type II cells. A hyperplastic pulmonary alveolus is illustrated in Fig. 15. Electron microscopically, aspects of the hyperplastic cells were evidently those of type II alveolar cells, although they showed some differ ences in ultrastructure from the normal type II cell. Mitochondria were large in size and irregular in shape (Fig. 16), and, occasionally, retention of huge osmiophilic lamellar bodies was noted in the cell cytoplasm (Fig. 16). Cristae mitochrondriales were arranged irregularly (Fig. 16), and well-developed endoplasmic reticulum was frequently seen in the cytoplasm (Fig. 17). Early stages of the membrane formation responsible for "cytoplasmic compartments" were ob served in the hyperplastic cell (arrow in Fig. 17). It is suggested that the membrane was derived from the endoplasmic reticulum. In many respects, the hyperplastic type II cell is assumed to be the precursor of the neoplastic cell. An intermediate form between type I and II cells was frequently observed in the hyperplastic pulmonary alveoli. The arrow in Fig. 15 indicates a part of the cell cytoplasm which may represent a transitional form between type I and II cells. Though the S.S? EC- 1351 294 YASt'NOSl'KF. SL'ZfKI attenuated cytoplasm corresponded to that of a type I cell, the presence of microvilli on the cell surface was characteristic of a type II cell. DISCUSSION Experimental studies (10-18) on the oncogenicity of vinyl chloride have re vealed that the monomer can induce various neoplasms including hepatic hemangiosarcoma (rat. mice, hamsters), Zymbal gland carcinoma in the external audi tory meatus (rats), breast cancer (mice), nephroblastoma (rats), "lung adenoma" (mice), skin trichoepithelioma (hamsters), lymphoma (hamsters), and fore stomach papilloma (hamsters). Evidence of the pulmonary oncogenicity of vinyl chloride in animals has been obtained: (i) Viola et al. (10, 11) have reporterLthat rats exposed to vinyl chloride exhibited lung cancer (32%). Histological features of the cancers were stated to be those of adenocarcinoma, with the exception of a single epidermoid tumor. Maltoni and Lefemine (12, 13), however, reviewed the histological slides of Viola et al. and stated that the lung cancers reported by the latter were not primarylumors pf the lungs, but metastatic cancers'TTorri"Zy mSaT glands. (it). Maltoni and Lefemine (12, 13) also hav^reported on the ~fnrtTnQttftry-Pficogcnicity of vinyl ! ; ; ! Fig. II. C 60,000. chloride o: carcinoma induced i ("adenom Fir.. 12. : section in if rt I.MONAKV Tl MORS INDL'Cl.l) lY VIXVL CMLOKIUt. X -ids' 295 o Fu,, II. Glycogen granules in a cisterna of the endoplasmic reticulum (2500 pom in croup Jin x 60.000. chloride on the basis of their own data. Though they could not find bronchogenic carcinoma in,rats, rare pulmonary hemanginsarr-nirmc and fibrosarcomas were induced In these animals. Unlike the-sftr.o milmrmarv tn^np ("adenomas") were found in mice (89 of 471). Maltoni and Lefemine (12, 13) 1 *i~3 , t 111 ' !| ''lit : i .lias =l@i' m$r^- Fic., 12. Single staining by uranyl acetate. Glycogen granules are not detected in the cisterna. A step section in the specimen of Fig. II. x 60,000. i -gaffs#. * i "t J : f {&?? G **>* & 2&.'r3s*&& * -_ irJ W i~3 r^LjfcfJ i %*- Essf .* sV EC- 13&3 '--V' liiife 296 YASUNOSL'KE Sl'ZVKI Fic. 13. Crystalloid structure seen in the cytoplasm of a neoplastic cell (2500 ppm in group III), x 30,000. noted that some of the adenomas underwent malignant transformation, (iii) Kcplinger and associates (14) have found "alveologenic adenomas" in the lungs of mice exposed to vinyl chloride (44 of 49). (iv) Lee and associates (15) have stated that "bronchiolar adenoma" developed in mice 2 months after exposure to vinyl chloride at 50-1000 ppm. (v) Holmberg and associates (16) found "alveologenic adenoma" in 13 of 24 mice exposed to vinyl chloride at 50 ppm for 24-52 weeks. Our present study has also confirmed that pulmonary tumors are frequently in duced by vinyl chloride (26 of 27). s, if''?* c l;.'. $ , . V *v*. ;7:' )i Vr. .AoJ TAJ V?/ `33 Fic.. 15. ! epithelium. / 4200. / r< - Fit;. 14. Poorly differentiated neoplastic cells. No osmiophilic lamellar bodies are observed (6000 ppm in group II). x 6200. Fic. 16. nitochondt  .>, lU'I.MOXAKV IIWIORS INIH^I.I) BY V|\VJ. CMl.OKIDK 0- V 297 Vi- \`VaS*K* ,\i tjrf* *f'&' ' f'1 't\/ii^,:*'% 'v"-;!. - .-.' V- ~ " ' v. 'i'i- V-J &;=v;7 .=,' ' : *1 . V^' * ii- * - /A -v`'`> ' ' 7 ' V,, ,/. \ - Fit;. 15. Part of a hyperplastic alveolus. Hyperplastic cells are identified as type II alveolar epithelium. An arrow indicates a transitional form between type I and II cells (2500 ppm in group 1) x 4200. stair '! it m f ,i /..sis as;-. V Tr<i;> `V3. j jAfFtf* jj --Kv ' Si-!' :..?*2^5J .? i :*i3| : iS *:t r- mm Ssa& " .............. .-- Sitri ,C * 11 rvJ.V$S Fit.. 16. A hyperplastic type II cell. A huge osmiophilic lamellar body and irregular cristae mitoeliondrialcs are seen (6000 ppm in group III), x 11.400. J'. * '' ''ytr2*~w ' -i* -. '-'/iv-A, - \Z- .ij-ii -- ''-r' * -" v "^r-t " V,* > t ;.V>V,tr? r^>tr 'Ik.--. * /v*'-** -i , V. fs -ly*,- V *\r % >v ; is -tSii-iSS/- r-- -fs . .'----- .".U.vr -V '" ir -r-i * , . t.'-V; EC- 1355 29S YASUNOSUKK SUZU KI Fic. 17. Cytoplasm of a hyperplastic type 11 cell. Arrows indicate membrane formation. Endoplas mic reticulum is well developed (2500 ppm in group III), x 26,600. The reports by Lee et al. (15) and Hblmberg et al. (16) are noteworthy since the pulmonary tumors are induced by low doses and relatively long exposure and also because these reports demonstrated that the oncogenicity of vinyl chloride is dose related. Based on all the data available, it can be concluded that, of all the tumors induced by vinyl chloride in all species, those in the lungs of mice appear earliest, and that mouse lung is an extremely sensitive organ for demonstrating the on' cogenicity of vinyl chloride. Gross anatomical and histological aspects of the tumors in our investigation corresponded to the "alveologenic tumor or cancer" of Stewart et al. (21, 22), though other designations such as pulmonary adenoma, bronchiolar adenoma, and adenoma becoming malignant have also been used. The alveologenic tumor has been induced by various carcinogens (21-26) such as polycyclic hydrocarbons, urethane, nitrogen mustard, methylcholanthrene, and nitrofur derivates and is known to occur spontaneously with aging (27--29). The cancer induced has been distinguished from that occurring spontaneously by multiple primary foci, occasional formation of huge tumors, and occurrence w-ithout any relation to aging. It is also known that in certain strains, such as A and DD, spontaneous tumors are quite common after 10 to 12 months of age. Spontaneous pulmonary tumors could be excluded in our experimental animals; in addition to the above' mentioned points, neoplastic changes in the lungs were absent in the controls. Electron microscopically, alveolar epithelium, particularly the type II cell, was assumed to be the precursor of vinyl chloride-induced tumor in the mouse lung. This assumption was derived from ultrastructural similarities between the normal type II cell and the neoplastic cell. Similar suggestions have been made by other investigators (20,26, 30) after studying pulmonary tumors induced by agents other than vinyl chloride. It was noteworthy that the processes of transformation of the normal alveolar epithelium into the neoplastic cell could be followed morphologically on the level of ultrastructure; the appearance of an intermediate form between type I and II cells in the alveolar lining, the disappearance of type II cell in the lining due to replacement by the hyperplastic type II cells, which were transformed from the intermediate form, and the neoplastic change of the type II cell were assumed to be a sequen cal conditio prior to cut cally, both t 34). It has fc immature al 34). Some similar in u these persp may be ink alveolar epi Recently, due to lung compared t< cally and w adenocarcir chogenic o cinogenesis Neopiast it is knowi veologenic I tion occurs tion of this fore dubbei Lafemine ( undergo trr ments, we < Alveolog ble to obsc precursor ti Hepatic I vinyl chlori animals (mi are almost i cells of vin;, these differchloride m: chemical. C lie aromati known to ir be associate carcinogens vinyl chlori We wish to EC- 1356 Bsy."BCTO*r. lTI.MONAKV TUMORS IMH'Ct l) UV VINVl, CHIOKIPK 299 be a sequence of the process. The intermediate form appears in certain pathologi cal conditions, such as pulmonary asbestosis (3J) and radiation pneumonitis (32) prior to cuboidal metaplasia of the attenuated alveolar epithelium. Embryologically. both type 1 and II cells are of the same origin, the entodermal epithelium (33. 34). It has been accepted that, at a late stage of gestation, rapid attenuation of the immature alveolar epithelium, similar to the type II cell, occurs in mammals (33. 34). Some of the neoplastic cells, distinguished as poorly differentiated, were similar in ultrastructure to the immature alveolar epithelium of fetal lung. From these perspectives, the process of neoplastic alteration observed in the epithelium may be interpreted as a retrograde process of the normal differentiations of the alveolar epithelium. Recently, VVaxweiler .anri-assoewuag rppnr^H ^p_im:reagg_H_niimher of deaths due to lung cancer among vinylxhloride^vorkers (8): Xhey observed 12 cases compared to the 1.1 cases expected. Eight of the twelve were examined histologi cally and were classifigd-as-undiffcrentiateri large^cell rarcinrjrnTmve cases') and adenocarcinoma (three casesT-Since these human lung cancers are of bronchogemc origin, it may be that target pulmonary cells in vinyl chloride car cinogenesis are "different InTiufnpTaTTaTiTousFlOTif.------ ---------------- --------- ^ Neoplastic invasion and metastases were not found in our material. However, it is known (21, 35-38) that sometimes both induced and spontaneous alveologenic tumors of mice show such changes and that the malignant transforma tion occurs with some delay after initiation of the tumor. In addition, transplanta tion of this tumor has been accomplished (39). Stewart and associates (21) there fore dubbed it an "alveologenic tumor" or "alveologenic cancer." Maltoni and Lafemine (13) have found that some vinyl chloride-induced pulmonary tumors undergo transformation. During the short period of observation in our experi ments, we did not observe this. Alveologenic tumors may be considered unique in some ways, since it is possi ble to observe the process of malignant transformation sequentially from the precursor to the malignant cell via hyperplastic and benign neoplastic states. Hepatic hemangiosarcoma is recognized as a specific malignant tumor related yinvT cruonde exposure. The tumor can be induced in a variety of experimental animals (mice, rats, and hamsters) (12, 13), and histological features of the tumor are almost identical in humans and animals. In contrast, me lntrapulmonary target cells of vinyl chloride oncogenesis may be different in humans and mice. Beyond these differences, moreover, the induction of alveologenic tumors in mice by vinyl chloride may be predictive of a risk of human bronchogenic cancer from the chemical. Consistent with this is the fact that various carcinogens such as polycyc lic aromatic hydrocarbons, nitrogen mustard, and chromate compounds are known to induce alveologenic tumors in mice, on one hand, and, on the other, to be associated with excess bronchogenic carcinoma among workers exposed to the carcinogens (40). It is noteworthy that a similar relation has been suggested for vinyl chloride. ACKNOWLEDGMENTS We wish to thank Mr. C. Din and Mr. R. Ashley for excellent technical assistance. Q 300 YASUNOSl'KK SLZLKI REFERENCES 1. Creech. J. L.. and Johnson, M. N. (1974). Angiosarcoma in the manufacture of polyvinyl chloride. J. On-up. Med. 16, 150-151. 2. Falk, H., Creech. J. L.. Heath, C. W., Jr., Johnson, M. N., and Key. M. M. (1974). Hepaticdisease among workers at a vinyl chloride polymerization plant. J. Amt-r. Med. Ass. 230, 59-63. 3. Block, J. B. (1974). Angiosarcoma of the liver follow ing vinyl chloride exposure. J. Amur. Mud. Ass. 229, 53 -54. 4. Lange, C. E., Jtihe, S., and Veltmun. G. (1974). Uber das Anftreten von Angiosarkomen der Leber von zwei Arbeitern der PVC-herstcllender Industrie. Dent. Med. Wochenschr. 31, 1593-1599. 5. Lee, F, L, and Harry D. S. (1974). Angiosarcoma of the liver in a vinyl chloride worker. Lancet 1, 1316-1319. 6. Thomas, L. B., Popper, H., Berk, P. D.. Selikofl'. I. J., and Falk, H. (1975). Vinyl chloride- induced liver disease. TV. Engl. J. Mud. 292, 17-22. 7. Nicholson, W. J., Hammond, E. C., Seidmqn, H., and Selikoff, I. J. (1975). Mortality experience of a cohort of vinyl chloride-polyvinyl chloride workers. Ann. NY Acad. Sci. 246, 225-236. Waxweiller, R. J., Stringer, W,, Jones, J., Wagoner, J. N., Falk, H., and Carter. C. (1976). Neoplastic risk among workers exposed to vinyl chloride. Ann. TV.)'. Acad. Sci. 21 \, 39-4S. Tabershaw, L. R., and Gaffcy, W. R. (1974). Mortality study of workers in the manufacture of vinyl chloride and its polymer. J. Occttp. Mud. 16", 506-516. 10. Viola, P. L. (1970). 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