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Influence of genetic strain on the induction of lung cancer in hamsters by alpha radiation
Europ. J. Cancer Vol. 9, pp. 825-828. Pergamon Press 1973. Printed in Great Britain
Influence of Genetic Strain on the Induction of Lung Cancer in Hamsters by Alpha Radiation* JOHN B. LITTLE, BARBARA N. GROSSMAN, ROBERT B. McGANDY and WILLIAM F. O'TOOLE Department of Physiology, Harvard University School of Public Health, Boston, Massachusetts 02115 U.S.A. Abstract--The response was studied of four inbred strains of Syrian hamsters to multiple intratracheal instillations of the alpha emitting radionuclide polonium-210 adsorbed onto hematite particles. Marked differences occurred among strains in their tolerance to the instillations. There also appeared to be significant differences in the tumor induction times, but thefrequency of lung tumors was similar in thefour strains-varying between 33~ and 50~o. The influence of genetic strain might well be more marked with chemical carcinogens in which mechanisms of activation or detoxification become importantfactors which come under genetic control.
would allow us to study factors which control sensitivity to carcinogens. We have investigated the influence of genetic strain on the response to repeated intratracheal instillations and on the susceptibility to lung tumor induction by polonium-210 (2a°Po, a naturally occurring radionuclide which emits a 5.3 MeV alpha particle) in four inbred hamster lines. 21°Po was chosen as a carcinogen because its activity does not depend on chemical activation or degradation in the animals, and it has been found reproducibly to yield a high incidence of lung tumors in random bred hamsters [10, 11 ].
INTRODUCTION SYRIAN golden hamsters have been widely used as test animals in carcinogenesis studies [1,2]. These investigations have employed random bred animals, although all laboratory hamsters are in reality derived from three animals originally brought to Israel from Syria in 1931 [3]. Recently, studies with inbred hamster lines have indicated an influence of genetic strain on susceptibility to polynuclear hydrocarbons following subcutaneous and gastric administration [4, 5] and on the response to adenovirus type 12 [6]. Syrian hamsters have received increasing use in the past several years in studies of experimental respiratory carcinogenesis [7]. The occurrence of spontaneous lung tumors in hamsters is rare, and the incidence of infectious and other pulmonary complications is also low [8, 9]. It would therefore be important to know whether an inbred line might be a better model for such studies on respiratory carcinogenesis. In addition, the occurrence of significant differences in response among strains
MATERIAL AND M E T H O D S Male and female hamsters in about equal proportions from four inbred lines were kindly supplied by Dr. Freddy Homburger of the BioResearch Institute, Cambridge, Massachusetts. These lines were identified as BIO 2.4 (originally LSH), BIO 4.22, BIO 15.16 and BIO 87.20, and are now available from TELACO, Bar Harbor, Maine 04609, U.S.A. At the time of this investigation, brother-sister matings had been carried out for 28-30, 39-41, 17-18 and 18-20 generations respectively in these lines. Further details as to the origin and character-
Accepted 9 October 1973. *Supported by Grants P-613 from the American Cancer Society, and ES-00002from the National Institutes of Health. 825
826
John B. Little, Barbara N. Grossman, Robert B. McGandy and William F. O' Toole
istics of these B I O hamsters have been reported [5]. The animals were housed 3-4 to a cage according to sex in an environment controlled room, and were fed Purina chow and water ad libitum. Intratracheal instillations were begun when the hamsters reached 10 weeks of age. Each animal received 15 weekly instillations of 0"2# Ci 210po absorbed on 1.5 mg of hematite particles and suspended in 0-1 ml of isotonic saline. Hamsters were lightly anesthetized with sodium brevitol i.p. prior to each instillation. Details concerning the preparation and intratracheal instillation of 21°Po suspensions have been described [10, 11]. The surviving animals were weighed either weekly or biweekly from the 4th through the 30th week after the beginning of treatment. The hamsters were sacrificed when moribund, the inflated lungs and trachea removed together, fixed in alcohol-formalin fixative and embedded in paraffin blocks. Sections 8 # thick were cut and stained with hematoxylin and eosin for pathological study. Sections were obtained from each lobe of the lungs, as well as at several levels in the trachea.
130" 120"
~
.
2
0
It0" 100" (.9
"-'-¢
o7
90" 80" 70"
60
TREATMENT PERIOO
,I
TIME (WEEKS) AFTER FIRST INSTILLATION
Average weight of hamsters of 4 genetic strains during and after a course of 15 weekly intratracheal instillations of O.2g Ci 21°Po on 1.5 mg hematiteparticles suspended in O"1 ml isotonic saline.
~/g°
1.
100" .j 80" 60-
w ~" 20 m
io zo so 40 so 60 To 8o 90 i~o TIME(WEEKS)AFTERFkRSTINST~LLATION Fig. 2. Cumulativesurvival of hamsters of 4 genetic strains during and after the course of 15 weekly intratracheal instillations of O.2p Ci =l°po. o
RESULTS
The changes in the average weight of the hamsters in the four groups during and after the course of intratracheal instillations are shown in Fig. 1. The initial weights are similar to those reported by Homburger et al. [5] for comparably aged animals. In each group the average weight of the males was slightly lower than that of the females. The 87-20 and 15.16 strains continued to gain weight during the treatment period, while that of the 4"22 hamsters remained constant. The 2.4 strain, however, showed a rapid decline in weight during the treatment period which continued until 5 weeks after the last instillation. The cumulative survival for each strain vs time after the first instillation is shown in Fig. 2. The lung tumor incidence data are
tabulated in Table 1, and data indicating the time of death for each animal and the presence or absence of lung tumors at autopsy are presented in Fig. 3. Only one tracheal tumor was found among these animals: a carcinosarcoma occurring in an 87"20 hamster which died 7 7 weeks after the first instillations. There were no sex related differences in tumor incidence or induction time. With the exception of the single carcinosarcoma of the trachea, the induced tumors all involved peripheral lung parenchyma. We categorize these as "combined" tumors [10, 11]
Table 1. Lung tumor incidence in hamsters receiving 15 weekly intratracheal instillations of 0.2# Ci polonium-2 i0
Tumor incidence No. of animals dead with no lung tumor
Strain
No. of animals autopsied*
2"4 4"22 15-16 87"20
39 32 33 40
No. of animals dead with malignant 5-15 wks 15-92wks lung tumors 18 11 0 8
11 13 22 16
10 8 11 16
*Does not include hamsters which died before fifth week of t r e a t m e n t .
% of all animals
% of animals surviving 15 wk treatment period
26% 25% 33% 40%
48% 38% 33% 50°/0
Influence o f Genetic Strain on the Induction of Lung Cancer in Hamsters by Alpha Radiation
.
2.4
.
.
.
4.22
.ai~
o ~'[~;~;;~b~o o
15.16
87.20
0
+-DIED WITH TUMORI
.
~+
80~o+ o+ 8
o-,,o ~ ~ 005
o +o
+$o$1+ , d ~ +
/+ +,~-+ +8
I
o oo
+o o
+o + ~ + ~ o
t~ o
I0 20 3(3 40 50 60 "gO 60 90 TIME OF DEATH (WEEKS) AFTER FIRST INSTILLATION
Fig. 3. Time of death of individual hamstersfrom each of the 4 groups. Crosses or zeros indicate whether or not lung tumors werepresent at the time of death.
because both adenomatous and epidermoid features are found in different fields of the same tumor (Fig. 4). Only three of the total tumors showed epidermoid characteristics alone; two of these appeared to be bronchial in origin. Categorization of these lesions as tumors was based on their replacement of supporting lung tissue. As in our previous report [11], invasion of bronchi, blood vessels and pleura was seen in instances of extensive involvement. There were no notable differences in the histopathologic detail of these tumors among the four experimental groups, though, on the whole, tumors in the 87"20 group appeared more extensive.
DISCUSSION These results indicate that significant differences do exist in the response of gentically inbred strains of Syrian hamsters to intratracheaUy administered 21°po. These differences appear to involve the tolerance of the animals to multiple intratracheal instillations, and the carcinogenic response to alpha radiation. As can be seen in Fig. 2, over 50% of animals of strains 2"4 and 4"22 died during the treatment period, whereas no deaths occurred amongst the 15-16 group. In parallel experiments, about 20% of random bred hamsters died during the treatment period [10], comparable to the results with the 87.20 strain in these experiments. The more resistant strains actually gained weight during the treatment period (Fig. 1); this gain was similar to that observed in untreated control animals (F. Homburger, personal communication). The reasons for the marked differences in the mortality experience after treatment are not entirely clear. It is possible that the 2"4 and 4"22 strains were more sensitive to the toxic (noncarcinogenic) effects of radiation on lung tissue, although pathological evidence to support this hypothesis was not present. The degree of inflammatory change, fibrosis and necrosis appeared grossly similar in animals of similar ages. Interestingly, the 87.20 strain is normally
827
an unusually long-lived hamster; its longevity under standard conditions is 670 days, as compared with 532 days for the 2.4 and 481 days for the 4-22 strain [5]. The differences in the frequency of lung tumors among the four strains were small (Table 1), although the overall tumor incidence was slightly higher among the 87.20 animals. In this regard, Homburger et al. [5] found that bronchiolar adenocarcinomas developed in 10% of 87.20 hamsters following subcutaneous administration of benz[a]anthracene, whereas no lung tumors developed in untreated controls nor in similarly treated hamsters of several other strains including 4.22 and 15.16. In general in their study, Homburger et al. [85] found that 87"20 hamsters were more susceptible to the induction of tumors by subcutaneous and gastric administration of polynuclear hydrocarbons than were the other strains. Although the frequency of lung tumors was similar, a difference in tumor induction time was apparent among the four strains in the present study. As can be seen in Fig. 3, lung tumors were found in eight of the seventeen 87"20 animals which died between weeks 51 and 80, whereas only one of nine 15.16 hamsters which died after week 51 had a tumor. Tumors found in 15.16 animals were grouped primar!ly between weeks 35 and 51 (Fig. 3); only one tumor occurred before week 35. Tumors in the 4.22 hamsters tended to group before week 25, however, and tumors occurred in only two of the nine hamsters which died between weeks 25 and 60. Both within and among all strains, late occurring tumors did not appear on the whole to be more extensive or advanced histologically than earlier tumors, although tumors in 87-20 hamsters dying at all times appeared more extensive than those in the other strains. These findings suggest that the induction time effect is real, and that it cannot be explained simply on the basis that tumors were recognized earlier in those strains in which the animals died sooner from other causes. Furthermore, they suggest that the tumor incidence in the 2"4 and 4"22 strains would not necessarily have been greater had the animals survived longer. The results indicate that genetic strain does have some influence on the response to multiple intratracheal instillations of 21°po. Radiation, however, deposits its energy at random in cells and thus acts directly to initiate the carcinogenic process. The influence of genetic strain might well be more marked with chemical carcinogens in which mechanisms of activation or detoxification become important factors which may come under genetic control
828
John B. Little, Barbara N. Grossman, Robert B. McGandy and William F. O' Toole
~ G l g l g 1. 2. 3. 4. 5.
6. 7. 8. 9.
10.
1 1.
F. HOMBURGER,Chemical carcinogenesis in the Syrian golden hamster. Cancer 23, 313 (1969). F. HOMBUROER,Chemical carcinogenesis in Syrian hamsters. Prog. exp. Tumor Res. 16, 152 (1972). S. ADT.ER, Origin of the golden hamster Cricetus auratus as a laboratory animal. Nature (Lond.) 162, 256 (1948). F. HOM~UROERand S.-S. HSUEH, Rapid induction of subcutaneous fibrosarcoma by 7,12-dimethylbenz(a)anthracene in an inbred line of Syrian hamsters. CancerRes. 30, 1449 (1970). F. HOMBUROER,S.-S. HSUE~, C. S. KERR and A. B. RUSSFXELD,Inherited susceptibility of inbred strains of Syrian hamsters to induction of subcutaneous sarcomas and mammary and gastrointestinal carcinomas by subcutaneous and gastric administration of polynuclear hydrocarbons. CancerRes. 32, 360 (1972). G.L. VAN HoosmR, JR., J. G. BuRrd~ and J. J. Tm~NTIN, Comparative susceptibility of non-inbred and strain LSH inbred Syrian hamsters to the oncogenic adenoviruses. Proc. Soc. exp. Biol. (N.Y.) 134, 427 (1970). P. NETTESHEX~, Respiratory carcinogenesis studies with the Syrian golden hamster: a review. Prog. exp. Tumour Res. 16, 185 (1972). U. SAFFIOTTI,F. CEFISand L. K. KOLB, A method for the experimental induction of bronchogenic carcinoma. CancerRes. 28~ 104 (1968). W. DONTENWILL,Experimental investigations on the effects of cigarette smoke inhalation on small laboratory animals. In Inhalation Cardnoger~sis (Edited by M. G. HANNA,JR., P. Nm"rESHEIMand J. R. GI~P.RT, AEC Symposium Series 18, 389 (1970). J.B. LITTLE, B. N. GROSSMANand W. F. O'TooLE, Respiratory Carcinogenesis in hamsters induced by polonium-210 alpha radiation and benzo[a]pyrene. In Morphology of Experimental Respiratory Carcinogenesis (Edited by P. NErrEsHEIM, M. G. HANNA,JR. and J. W. DEATHE~OE, JR., AEC Symposium Series 21, 383 (1970). J . B . LITTLE, B. N. GROSSMANand W. F. O'TooLE, Factors influencing the induction of lung cancer in hamsters by intratracheal administration of polonium-210. In Radionudide Carcinogenesis AEC Symposium Series (In press, 1973).
Fig, 4.
Peripheral lung Jield f rom 15.16 hamster which died 45 weeks after first instillation with an extensive tumor. This jield shows a poorly daxerentiated efiidermoid pattern x 400, H C? E).
(to face p. 828)
Influence of Genetic Strain on the Induction of Lung Cancer in Hamsters by Alpha Radiation* JOHN B. LITTLE, BARBARA N. GROSSMAN, ROBERT B. McGANDY and WILLIAM F. O'TOOLE Department of Physiology, Harvard University School of Public Health, Boston, Massachusetts 02115 U.S.A. Abstract--The response was studied of four inbred strains of Syrian hamsters to multiple intratracheal instillations of the alpha emitting radionuclide polonium-210 adsorbed onto hematite particles. Marked differences occurred among strains in their tolerance to the instillations. There also appeared to be significant differences in the tumor induction times, but thefrequency of lung tumors was similar in thefour strains-varying between 33~ and 50~o. The influence of genetic strain might well be more marked with chemical carcinogens in which mechanisms of activation or detoxification become importantfactors which come under genetic control.
would allow us to study factors which control sensitivity to carcinogens. We have investigated the influence of genetic strain on the response to repeated intratracheal instillations and on the susceptibility to lung tumor induction by polonium-210 (2a°Po, a naturally occurring radionuclide which emits a 5.3 MeV alpha particle) in four inbred hamster lines. 21°Po was chosen as a carcinogen because its activity does not depend on chemical activation or degradation in the animals, and it has been found reproducibly to yield a high incidence of lung tumors in random bred hamsters [10, 11 ].
INTRODUCTION SYRIAN golden hamsters have been widely used as test animals in carcinogenesis studies [1,2]. These investigations have employed random bred animals, although all laboratory hamsters are in reality derived from three animals originally brought to Israel from Syria in 1931 [3]. Recently, studies with inbred hamster lines have indicated an influence of genetic strain on susceptibility to polynuclear hydrocarbons following subcutaneous and gastric administration [4, 5] and on the response to adenovirus type 12 [6]. Syrian hamsters have received increasing use in the past several years in studies of experimental respiratory carcinogenesis [7]. The occurrence of spontaneous lung tumors in hamsters is rare, and the incidence of infectious and other pulmonary complications is also low [8, 9]. It would therefore be important to know whether an inbred line might be a better model for such studies on respiratory carcinogenesis. In addition, the occurrence of significant differences in response among strains
MATERIAL AND M E T H O D S Male and female hamsters in about equal proportions from four inbred lines were kindly supplied by Dr. Freddy Homburger of the BioResearch Institute, Cambridge, Massachusetts. These lines were identified as BIO 2.4 (originally LSH), BIO 4.22, BIO 15.16 and BIO 87.20, and are now available from TELACO, Bar Harbor, Maine 04609, U.S.A. At the time of this investigation, brother-sister matings had been carried out for 28-30, 39-41, 17-18 and 18-20 generations respectively in these lines. Further details as to the origin and character-
Accepted 9 October 1973. *Supported by Grants P-613 from the American Cancer Society, and ES-00002from the National Institutes of Health. 825
826
John B. Little, Barbara N. Grossman, Robert B. McGandy and William F. O' Toole
istics of these B I O hamsters have been reported [5]. The animals were housed 3-4 to a cage according to sex in an environment controlled room, and were fed Purina chow and water ad libitum. Intratracheal instillations were begun when the hamsters reached 10 weeks of age. Each animal received 15 weekly instillations of 0"2# Ci 210po absorbed on 1.5 mg of hematite particles and suspended in 0-1 ml of isotonic saline. Hamsters were lightly anesthetized with sodium brevitol i.p. prior to each instillation. Details concerning the preparation and intratracheal instillation of 21°Po suspensions have been described [10, 11]. The surviving animals were weighed either weekly or biweekly from the 4th through the 30th week after the beginning of treatment. The hamsters were sacrificed when moribund, the inflated lungs and trachea removed together, fixed in alcohol-formalin fixative and embedded in paraffin blocks. Sections 8 # thick were cut and stained with hematoxylin and eosin for pathological study. Sections were obtained from each lobe of the lungs, as well as at several levels in the trachea.
130" 120"
~
.
2
0
It0" 100" (.9
"-'-¢
o7
90" 80" 70"
60
TREATMENT PERIOO
,I
TIME (WEEKS) AFTER FIRST INSTILLATION
Average weight of hamsters of 4 genetic strains during and after a course of 15 weekly intratracheal instillations of O.2g Ci 21°Po on 1.5 mg hematiteparticles suspended in O"1 ml isotonic saline.
~/g°
1.
100" .j 80" 60-
w ~" 20 m
io zo so 40 so 60 To 8o 90 i~o TIME(WEEKS)AFTERFkRSTINST~LLATION Fig. 2. Cumulativesurvival of hamsters of 4 genetic strains during and after the course of 15 weekly intratracheal instillations of O.2p Ci =l°po. o
RESULTS
The changes in the average weight of the hamsters in the four groups during and after the course of intratracheal instillations are shown in Fig. 1. The initial weights are similar to those reported by Homburger et al. [5] for comparably aged animals. In each group the average weight of the males was slightly lower than that of the females. The 87-20 and 15.16 strains continued to gain weight during the treatment period, while that of the 4"22 hamsters remained constant. The 2.4 strain, however, showed a rapid decline in weight during the treatment period which continued until 5 weeks after the last instillation. The cumulative survival for each strain vs time after the first instillation is shown in Fig. 2. The lung tumor incidence data are
tabulated in Table 1, and data indicating the time of death for each animal and the presence or absence of lung tumors at autopsy are presented in Fig. 3. Only one tracheal tumor was found among these animals: a carcinosarcoma occurring in an 87"20 hamster which died 7 7 weeks after the first instillations. There were no sex related differences in tumor incidence or induction time. With the exception of the single carcinosarcoma of the trachea, the induced tumors all involved peripheral lung parenchyma. We categorize these as "combined" tumors [10, 11]
Table 1. Lung tumor incidence in hamsters receiving 15 weekly intratracheal instillations of 0.2# Ci polonium-2 i0
Tumor incidence No. of animals dead with no lung tumor
Strain
No. of animals autopsied*
2"4 4"22 15-16 87"20
39 32 33 40
No. of animals dead with malignant 5-15 wks 15-92wks lung tumors 18 11 0 8
11 13 22 16
10 8 11 16
*Does not include hamsters which died before fifth week of t r e a t m e n t .
% of all animals
% of animals surviving 15 wk treatment period
26% 25% 33% 40%
48% 38% 33% 50°/0
Influence o f Genetic Strain on the Induction of Lung Cancer in Hamsters by Alpha Radiation
.
2.4
.
.
.
4.22
.ai~
o ~'[~;~;;~b~o o
15.16
87.20
0
+-DIED WITH TUMORI
.
~+
80~o+ o+ 8
o-,,o ~ ~ 005
o +o
+$o$1+ , d ~ +
/+ +,~-+ +8
I
o oo
+o o
+o + ~ + ~ o
t~ o
I0 20 3(3 40 50 60 "gO 60 90 TIME OF DEATH (WEEKS) AFTER FIRST INSTILLATION
Fig. 3. Time of death of individual hamstersfrom each of the 4 groups. Crosses or zeros indicate whether or not lung tumors werepresent at the time of death.
because both adenomatous and epidermoid features are found in different fields of the same tumor (Fig. 4). Only three of the total tumors showed epidermoid characteristics alone; two of these appeared to be bronchial in origin. Categorization of these lesions as tumors was based on their replacement of supporting lung tissue. As in our previous report [11], invasion of bronchi, blood vessels and pleura was seen in instances of extensive involvement. There were no notable differences in the histopathologic detail of these tumors among the four experimental groups, though, on the whole, tumors in the 87"20 group appeared more extensive.
DISCUSSION These results indicate that significant differences do exist in the response of gentically inbred strains of Syrian hamsters to intratracheaUy administered 21°po. These differences appear to involve the tolerance of the animals to multiple intratracheal instillations, and the carcinogenic response to alpha radiation. As can be seen in Fig. 2, over 50% of animals of strains 2"4 and 4"22 died during the treatment period, whereas no deaths occurred amongst the 15-16 group. In parallel experiments, about 20% of random bred hamsters died during the treatment period [10], comparable to the results with the 87.20 strain in these experiments. The more resistant strains actually gained weight during the treatment period (Fig. 1); this gain was similar to that observed in untreated control animals (F. Homburger, personal communication). The reasons for the marked differences in the mortality experience after treatment are not entirely clear. It is possible that the 2"4 and 4"22 strains were more sensitive to the toxic (noncarcinogenic) effects of radiation on lung tissue, although pathological evidence to support this hypothesis was not present. The degree of inflammatory change, fibrosis and necrosis appeared grossly similar in animals of similar ages. Interestingly, the 87.20 strain is normally
827
an unusually long-lived hamster; its longevity under standard conditions is 670 days, as compared with 532 days for the 2.4 and 481 days for the 4-22 strain [5]. The differences in the frequency of lung tumors among the four strains were small (Table 1), although the overall tumor incidence was slightly higher among the 87.20 animals. In this regard, Homburger et al. [5] found that bronchiolar adenocarcinomas developed in 10% of 87.20 hamsters following subcutaneous administration of benz[a]anthracene, whereas no lung tumors developed in untreated controls nor in similarly treated hamsters of several other strains including 4.22 and 15.16. In general in their study, Homburger et al. [85] found that 87"20 hamsters were more susceptible to the induction of tumors by subcutaneous and gastric administration of polynuclear hydrocarbons than were the other strains. Although the frequency of lung tumors was similar, a difference in tumor induction time was apparent among the four strains in the present study. As can be seen in Fig. 3, lung tumors were found in eight of the seventeen 87"20 animals which died between weeks 51 and 80, whereas only one of nine 15.16 hamsters which died after week 51 had a tumor. Tumors found in 15.16 animals were grouped primar!ly between weeks 35 and 51 (Fig. 3); only one tumor occurred before week 35. Tumors in the 4.22 hamsters tended to group before week 25, however, and tumors occurred in only two of the nine hamsters which died between weeks 25 and 60. Both within and among all strains, late occurring tumors did not appear on the whole to be more extensive or advanced histologically than earlier tumors, although tumors in 87-20 hamsters dying at all times appeared more extensive than those in the other strains. These findings suggest that the induction time effect is real, and that it cannot be explained simply on the basis that tumors were recognized earlier in those strains in which the animals died sooner from other causes. Furthermore, they suggest that the tumor incidence in the 2"4 and 4"22 strains would not necessarily have been greater had the animals survived longer. The results indicate that genetic strain does have some influence on the response to multiple intratracheal instillations of 21°po. Radiation, however, deposits its energy at random in cells and thus acts directly to initiate the carcinogenic process. The influence of genetic strain might well be more marked with chemical carcinogens in which mechanisms of activation or detoxification become important factors which may come under genetic control
828
John B. Little, Barbara N. Grossman, Robert B. McGandy and William F. O' Toole
~ G l g l g 1. 2. 3. 4. 5.
6. 7. 8. 9.
10.
1 1.
F. HOMBURGER,Chemical carcinogenesis in the Syrian golden hamster. Cancer 23, 313 (1969). F. HOMBUROER,Chemical carcinogenesis in Syrian hamsters. Prog. exp. Tumor Res. 16, 152 (1972). S. ADT.ER, Origin of the golden hamster Cricetus auratus as a laboratory animal. Nature (Lond.) 162, 256 (1948). F. HOM~UROERand S.-S. HSUEH, Rapid induction of subcutaneous fibrosarcoma by 7,12-dimethylbenz(a)anthracene in an inbred line of Syrian hamsters. CancerRes. 30, 1449 (1970). F. HOMBUROER,S.-S. HSUE~, C. S. KERR and A. B. RUSSFXELD,Inherited susceptibility of inbred strains of Syrian hamsters to induction of subcutaneous sarcomas and mammary and gastrointestinal carcinomas by subcutaneous and gastric administration of polynuclear hydrocarbons. CancerRes. 32, 360 (1972). G.L. VAN HoosmR, JR., J. G. BuRrd~ and J. J. Tm~NTIN, Comparative susceptibility of non-inbred and strain LSH inbred Syrian hamsters to the oncogenic adenoviruses. Proc. Soc. exp. Biol. (N.Y.) 134, 427 (1970). P. NETTESHEX~, Respiratory carcinogenesis studies with the Syrian golden hamster: a review. Prog. exp. Tumour Res. 16, 185 (1972). U. SAFFIOTTI,F. CEFISand L. K. KOLB, A method for the experimental induction of bronchogenic carcinoma. CancerRes. 28~ 104 (1968). W. DONTENWILL,Experimental investigations on the effects of cigarette smoke inhalation on small laboratory animals. In Inhalation Cardnoger~sis (Edited by M. G. HANNA,JR., P. Nm"rESHEIMand J. R. GI~P.RT, AEC Symposium Series 18, 389 (1970). J.B. LITTLE, B. N. GROSSMANand W. F. O'TooLE, Respiratory Carcinogenesis in hamsters induced by polonium-210 alpha radiation and benzo[a]pyrene. In Morphology of Experimental Respiratory Carcinogenesis (Edited by P. NErrEsHEIM, M. G. HANNA,JR. and J. W. DEATHE~OE, JR., AEC Symposium Series 21, 383 (1970). J . B . LITTLE, B. N. GROSSMANand W. F. O'TooLE, Factors influencing the induction of lung cancer in hamsters by intratracheal administration of polonium-210. In Radionudide Carcinogenesis AEC Symposium Series (In press, 1973).
Fig, 4.
Peripheral lung Jield f rom 15.16 hamster which died 45 weeks after first instillation with an extensive tumor. This jield shows a poorly daxerentiated efiidermoid pattern x 400, H C? E).
(to face p. 828)