[CANCER RESEARCH 49, 5848-5851. November I, 1989]

Enhancement of Pancreatic Carcinogenesis in Hamsters Fed a High-Fat Dietad Libitum and at a Controlled Calorie Intake1

Diane F. Birt,2 Alan D. Julius, Lenora T. White, and Parviz M. Pour

Eppley Institute for Research in Cancer [D. F. B., A. D. J., L. T. W., P. M. P.] and Departments of Biochemistry [D. F. B.J, Pharmaceutical Sciences [D. F. B.J, andPathology/Microbiology ¡P.M. P.], University of Nebraska Medical Center, Omaha, Nebraska 68105-1065

ABSTRACT

An enhancement of pancreatic cancer induced by /V-nitrosobis-(2-oxopropyl)amine (BOP) was reported previously in Syrian hamsters fedhigh-fat diet following carcinogen treatment. The purpose of our researchwas to determine if this enhancement was due to the consumption ofmore calories by the hamsters fed the high-fat diet. Male hamsters weretreated with a single injection of BOP (20 mg/kg body weight s.c.) at 8weeks of age. One week later they started either on a low-fat diet (4.3%corn oil) or a high-fat diet (20.5% corn oil) that was fed until the end ofthe experiment at 92 weeks after BOP. Diets were fed either ml libitumor in a control-fed protocol. The control-fed groups had equivalent calorieintakes and were restricted slightly in comparison with the ad libitum-fed hamsters. BOP treatment reduced survival slightly but survival didnot differ significantly in accordance with dietary assignment. Bodyweight was elevated in the hamsters fed high-fat diet ad libitum incomparison with those fed low-fat diet ad libitum. However, differenceswere not observed in hamsters fed low- and high-fat diets by the control-fed protocol. Pancreatic carcinogenesis was enhanced about 3- to 4-foldwhen hamsters were fed high-fat diet by either protocol. The degree ofenhancement did not differ with the feeding regimen. However, the higherdeath rate with pancreatic cancer occurred earlier in the ad libitum-fedhamsters than in the control-fed hamsters.

INTRODUCTION

We found a 5- to 6-fold increase in pancreatic cancer inducedby BOP3 in hamsters fed diets containing 20.5% corn oil

compared with hamsters fed 4.3% corn oil following BOPtreatment (1, 2). This enhancement by high-corn oil diets fedad libitum was observed at control protein levels (18 g/386kcal) and high protein levels (36 g/385 kcal), but not at lowprotein levels (9 g/386 kcal) (2). The increased tumor yield inthis experiment may have been caused by an elevated calorieconsumption as reflected by increased body weights in all thehigh-fat groups (1, 2).

Studies on the relationship between calorie intake and carcinogenesis have demonstrated a striking inhibition of tumori-genesis at sites such as mammary glands (3), colon (4), skin (5),and pancreas (6) in diet-restricted animals (reviewed in Ref. 7).Investigations into the interaction between calorie intake anddietary fat intake on mammary carcinogenesis suggest that theinfluence of dietary fat on carcinogenesis in part may be attributed to elevated calorie intake in rodents fed high-fat diets (8).

This study aims to determine if the increased pancreaticcancer in hamsters fed high-fat diet was due to the elevatedcalorie intake by these animals.

MATERIALS AND METHODS

Male Syrian hamsters were obtained from the Eppley Institute colony(Unei:SYR) at 6 weeks of age. The average body weight was 79 ±1

Received 3/6/89; revised 7/14/89; accepted 7/26/89.The costs of publication of this article were defrayed in part by the payment

of page charges. This article must therefore be hereby marked advertisement inaccordance with 18 U.S.C. Section 1734 solely to indicate this fact.

1This work was supported by NIH Grants RO1CA 31655 and CA-36727 andby Grant SIG-16 from the American Cancer Society.

2To whom requests for reprints should be addressed, at Eppley Institute for

Research in Cancer and Allied Diseases, 42nd and Dewey Ave., Omaha, NE68105-1065.

J The abbreviation used is: BOP, iV-nitrosobis-(2-oxopropyl)amine.

(SE) g, and they were fed the control semipurified diet shown in Table1 for the first 2 weeks of the experiment. Eight-week-old hamsters wererandomized into the 8 treatment groups shown in Table 2. They weretreated once with 20 mg BOP/kg body weight (s.c.) in physiologicalsaline or saline alone. One week later they were given their assigneddietary treatment. In the ad ¡ibitum-fedgroups, hamsters were allowedfree access to the low- or high-fat diet for the remainder of theexperiment. For training in equivalent calorie consumption, the control-fed groups were given the assigned diets in a pair-fed pattern forthe first 20 weeks following BOP treatment. The low-fat diet andcontrol-fed hamsters were maintained on the diet 8 h/day for the firstweek of this period. Thereafter the diet was provided for 16 h/day.Their food intake was measured and the distribution of their calorieconsumption was fed to the high-fat/control-fed hamsters such thatthere were high-consumption high-fat hamsters paired to high-consumption low-fat/control-fed hamsters and low-consumption high-fat/control-fed hamsters paired to low-consumption low-fat/control-fedhamsters. At 20 weeks after BOP treatment it became apparent thatthe high-fat/control-fed hamsters were not consuming all of theirallotment and that some of the low-fat/control-fed hamsters were losingweight. For these reasons we allowed the control-fed groups unlimitedaccess to food. Their intake was monitored daily. If the distribution ofcalorie consumption by the high-fat and control-fed hamsters exceededtheir low-fat/control-fed diet counterparts, the high-consuming hamsters in this high-fat group were identified and fed reduced allotmentsfor 1 week to retrain them to consume fewer calories. Less than 10%of the hamsters in the high-fat/control-fed group required retraining.

Hamsters were housed in temperature (21 ±2°C)-and humidity (40

±5%)-controlled facilities with a light-dark cycle of 12-h/12-h and 10air exchanges/h. Hamsters in the ad libitum- and control-fed groupswere caged in groups of five and singly, respectively, in corncob bedding(Bed-O-Cobs; Anderson Cob Co., Maumee, OH).

The experimental low-fat and high-fat diets are shown in Table 1.The diet termed "low-fat" actually contains a control level of dietary

fat. However, to avoid confusion with the control feeding protocol, weare calling this diet low-fat. We used these diet formulations in previousstudies with Syrian hamsters (1, 2), in which the diets improved survivaland were useful in demonstrating the enhancement of pancreatic carcinogenesis in hamsters fed high-fat diet. These diets are formulated sothat protein, vitamin, mineral, and fiber intake remains constant perkcal. Thus, with hamsters consuming equivalent calorie allotments, theonly differences in intake will be increased calories from fat anddecreased calories from carbohydrates in hamsters fed high-fat diets incomparison with those fed low-fat diets.

Hamsters were killed when moribund or at week 94 of the experimentwhen only 40% of the hamsters remained alive. Pancreases were removed, fixed in Bouin's fixative, and stained with hematoxylin and

eosin according to conventional methods. The pancreatic lesions werecoded by previously published criteria (9).

Carcasses of hamsters killed at the end of the experiment were groundand lyophilized and carcass lipid and protein were determined. Lipidwas determined gravimetrically following extraction with petroleumether in a Soxhlet extractor and evaporation of the solvent. Protein wasdetermined by the micro-Kjeldahl procedure (10).

Data on body weight, food consumption, and carcass compositionwere assessed statistically by analysis of variance (11). Individual meanswere compared using a i test based on the residual mean square fromthe analysis of variance. Data on lesions were compared using the v'

test. In instances in which improved longevity was associated withincreased incidence, data were age adjusted by the methods of Peto etal. (12). Data are presented as weeks of the experiment.

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PANCREAS CANCER, DIETARY FAT, AND CALORIE CONTROL

Table 1 Expérimentâtdiets

% of composition

Ingredients"Corn

oilCaseinDextrinDextroseVitamins

(Teklad vitaminsupplementation)Minerals(Wm.Briggs)FeSO4-H2ONonnutritive

fiberLow-fat4.317.148.316.11.43.30.029.5High-fat20.520.531.810.31.74.00.0211.4

Total

Calorie density (kcal/g)% of calories from fat

100

3.610.0

100

4.341.0

' All ingredients with the exception of the ferric sulfate were purchased from

Teklad test diets (Madison, WI). The compositions of vitamin and mineral mixeswere described previously (1, 2).

Table 2 Treatment protocol

Carcinogen treatment(mg BOP/kg bodywt)°020Feeding regimenad

libitumadlibitumControl-fedControl-fedail

libitumadlibitumControl-fedControl-fedDietary

fatlevelLowHighLowHighLowHighLowHighNo.of

hamsters3025303030353030

" Administered at 8 weeks of age in physiological saline.

Table 3 Calorie consumption of hamsters fed low- and high-fatdiets'Type

offeedingSaline

adlibitumControlledBOP

adlibitumControlledLevel

ofdietaryfatLow

HighLow

HighLow

HighLow

HighWk

of experiment(kcal/day)51-6030

(B)34(C)26

(A)26(A)30

(B)35(C)26

(A)28 (A, B)71-7529

(B)35(C)28

(A, B)27 (A,B)29

(B)35(C)27

(A, B)27 (A, B)

* Each value represents the average of 300 to 1000 observations; SEM = 1-2.

Significant effects of type of feeding and dietary fat observed by analysis ofvariance (P < 0.01). Results of r test comparisons indicated by: (A) < (B) < (C)(P < 0.05). Values with two letters were not statistically different from valueswith either of those letters.

RESULTS

Average calorie consumption during two representative periods of the experiment when the hamsters were allowed accessto food following training is shown in Table 3. Hamsters in thecontrol-fed/low-fat and control-fed/high-fat groups consumedsimilar calorie allotments. Ad libitum-fed hamsters generallyconsumed more calories and the high-fat/ad libitum-fed hamsters had the highest calorie intake.

Body weights at weeks 4, 40, and 94 of the experiment areshown in Table 4. Hamsters in the control-fed groups gainedlittle weight and their weights did not differ according to thediet fed. In contrast, the ad libitum-fed hamsters gained weightuntil about week 40 and lost some weight thereafter. In addition, the hamsters fed high-fat diet ad libitum weighed morethan those fed low-fat diet ad libitum. Treatment with BOP didnot influence body weight.

Survival at weeks 40 and 60 of the experiment was 99 and90%, respectively. At these times no differences in survivalbetween the treatment groups were found. By week 94, 51 % of

the hamsters in the non-BOP-treated groups and 29% of thehamsters in the BOP-treated groups had survived (P< 0.01 byX2 analysis). Among non-BOP-treated hamsters and BOP-

treated hamsters on the control fed protocol, survival wasextended slightly (15%) in the hamsters fed high-fat diet incomparison with those fed low-fat diet (Table 5). These dietaryeffects on survival were not statistically significant.

The percentage of body lipid and protein (Table 6) was notinfluenced by feeding protocol and, therefore, the data werepooled across this variable. Carcass lipid was elevated in hamsters fed the high-fat diet following BOP treatment, but differences were not observed in the saline-treated hamsters. Carcasslipid and protein were reduced in the carcinogen-treated ham

sters but only the lipid reduction was statistically significant.Feeding the high-fat diet increased pancreatic carcinogenesis

in both ad libitum- and control-fed hamsters as shown in Table5. These data were age adjusted to correct for the possibilitythat some of the effect of high-fat diet on pancreatic cancer wasdue to an effect of dietary fat improving longevity (Table 7).The results of this analysis demonstrated that the excess ofcancers in the high-fat groups occurred from weeks 60 to 79 inad libitum-fed hamsters and from weeks 80 to 94 in control-

fed hamsters. This observation indicates that hamsters developed more tumors when fed high-fat diet but that the excessdeath rate of hamsters with cancer was delayed when the dietswere control fed. Further, the earliest adenocarcinoma wasobserved in an ad libitum-fed hamster at 42 weeks, whereas incontrol-fed hamsters such lesions were not seen until after week70. The average survival of hamsters with carcinoma was increased in control-fed hamsters given high-fat diet in comparison with ad libitum-fed hamsters given high-fat diet (Table 5),but the difference was not statistically significant. Of the observed carcinomas, 19% were carcinoma in situ, 19% wereintraductular carcinoma, 17% were microcarcinoma, and 45%were adenocarcinoma. The distribution of carcinoma type wasnot significantly influenced by dietary protocol.

BOP-treated hamsters had fewer ductular adenomas in thelow-fat/control-fed group in comparison with all other BOP-treated groups (Table 8). Age adjustment of these data demonstrated that this relationship was statistically significant incomparing hamsters in these groups killed from weeks 60 to79 or from week 90 to week 94. Non-BOP-treated hamstersdeveloped fewer adenomas. Acinar cell nodules developed onlyin the hamsters fed high-fat diet ad libitum (12% incidence, 0.8acinar cell nodule/effective animal).

Hamsters fed high-fat diet by either feeding protocol following BOP treatment also had elevated incidences of pancreaticductular hyperplasia (51% in hamsters fed high-fat diet and28% in those fed low-fat diet; P < 0.02) and dysplasia of ductalcells (19% in high-fat groups and 6% in low-fat groups; P <0.05). In addition, both carcinogen- and non-carcinogen-treatedhamsters fed high-fat diet had more pancreatic islet hyperplasia(7%) in comparison with hamsters fed low-fat diet (1%; P <0.05).

Gallbladder and pancreatic lesions, which were influenced bythe feeding protocol but were not influenced by dietary fat levelor BOP treatment, are shown in Table 9. Control-fed hamstershad higher incidence of gallbladder hyperplasia, pancreaticfibrosis, and pancreatitis but lower incidence of gallbladderinflammation and pancreatic lipomatosis. Gallbladder andcommon duct polyps were observed in 43 and 28%, respectively,of the BOP-treated hamsters and 4 and 1%, respectively, of thenon-BOP-treated animals. Gallbladder adenocarcinomas werefound in 4% of the BOP-treated hamsters. None of these lesionswere altered significantly by the dietary treatments.

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PANCREAS CANCER, DIETARY FAT, AND CALORIE CONTROL

Table 4 Body weights of hamsters fed low- and high-fat diets with BOP

Low-fattreatmentWithoutWithoutWithoutWithWithWithWk4409444094n3029153030gAd

libitumMean

±SEM11013811511313633(B)°433(B)1

12 ±5 (A)n30301530308ControlledMean

±SEM110±3119±

3(A)112±4109

±3118±3(A)107±5 (A)High-fatAd

libitumn25241435359Mean104

±154±117±1IO±152

±129±±SEM33(C)422(C)5(B)n303017303010ControlledMean

±SEM113±3119

±3(A)113±3108

±3114±3(A)109

±5 (A)' f test comparisons within each week: A < B < C (P < 0.05).

Table 5 Survival and pancreatic ductular carcinoma yield in hamsters fed low- and high-fat diets by ad litibum or control-fed protocol"

CarcinogentreatmentWithoutWithoutWithoutWithoutWithWithWithTypeoffeedingad

libitumControl-fedml

libitumControl-fedLevelof

fatLowHighLowHighLowHighLowHigh%survivingat

95wk5058505727262733No.

ofeffectivehamsters2424292624333024Overallincidence(%)00008

(A)30(B)13(C)52

(D)No.

ofCRC*/EAN0.00.00.00.00.2

(A)0.6(B)0.2

(A)0.8(B)Av.

survivalofCRC-bearinghamsters(wk

±SD)75

±2280±1875

±488±10

" x1 test comparisons on age-adjusted data within each column: A < B, C < D, (P < 0.05).* CRC, carcinoma; EAN, effective animal.

Table 6 Percentage of body lipid and protein in hamsters fed low- and high-fatdiets and treated with BOP"

Carcinogen(mg

BOP/kgbodywt)002020fatlevelLowHighLowHighNo.

ofobservations5567Mean%ofcarcasslipid8.1

±0.8(B)8.8±0.8(B)4.9

±0.7(A)7.4±0.6 (B)±SEM%

ofcarcassprotein18.0

±1.518.2±1.516.2

±1.316.5±1.2

" Analysis of hamsters on the experiment for 94 weeks. Data were pooledacross method of feeding since significant differences were not observed. Significant effect of BOP and dietary fat observed by analysis of variance (P < 0.05)results of t test comparison indicated by: A < B (P < 0.05).

DISCUSSION

In the present experiment, pancreatic ductal/ductular carci-nogenesis was enhanced in hamsters fed high-fat diets irrespective of calorie consumption. In particular, ad libitum consumption of the high-fat diet was accompanied by consumption ofmore calories and elevated body weight whereas control-fedhamsters given the low- and high-fat diets consumed equivalentcalorie allotments and did not differ in body weight. Theincreased pancreatic cancer rate in hamsters fed high-fat dietwas observed among hamsters dying between weeks 60 and 79in ad libitum-ïeàgroups and among hamsters dying between

weeks 80 and 94 in control-fed hamsters. The delay in the lattergroup could have been due to an increase in the latency ofpancreatic cancer in the control-fed hamsters or to the aggressiveness of cancers in the ad libitum group. Inasmuch as hamsters in the control-fed groups were dying during weeks 60-79with pancreatic cancer but cancer rates were not significantlyassociated with dietary fat (Table 7), it seems more likely thatthe latency of the tumors was increased in some hamsters inthe control-fed/high-fat group.

Studies from other laboratories have suggested that caloriesmore profoundly modified breast and colon carcinogenesis thandietary fat levels. For example, Boissoneault et al. (13) compared ad libitum consumption of low- and high-fat diets withthe restricted high-fat diet fed at the equivalent net energy valueconsumed by the low-fat group. Net energy value was calculatedfrom values published earlier (14). Their results showed thatrestricting the high-fat diet to a net energy value equivalent tothat consumed by the ad libitum low-fat group inhibited 7,12-dimethylbenz(a)anthracene-induced mammary carcinogenesis.Klurfeld et al. (15) observed that restricting high-fat diets significantly inhibited mammary and colon tumorigenesis andsuggested that calorie intake was probably more important thanfat intake per se in determining cancer rates. However, thesestudies used diets containing about 13% fat in the high-fat-restricted group, a level which was not effective in the enhance-

Table 7 Age-specific rates of pancreatic adenocarcinoma in BOP-treated hamsters fed low- and high-fat diets by ad libitum or control-fed protocol'

Type offeedingAd

libitumControl-fedExperimental

wk40-59

60-7980-9440-59

60-7980-94No.

of hamsters dying3

11102

1513Low-fatIncidence(%)33

0(A)10020

8 (A)No.

ofCRC*/EAN0.33

0.00 (C)0.20.00

0.270.15(C)No.

of hamsters dying2

8230

1014High-fatIncidence

(%)50

38 (B)2640

64 (B)No.

ofCRC/EAN0.50

0.88 (D)0.480.60

l.OO(D)°Results of x1 tests within each row using age adjustment according to the method of Peto (12); A < B, C < D (P < 0.05).* CRC, carcinoma; EAN, effective animal.

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PANCREAS CANCER, DIETARY FAT, AND CALORIE CONTROL

Table 8 Pancreatic ductular adenoma yield in hamsters fed low- and high-fat diets by ad libitum or control-fed protocol

CarcinogentreatmentWithout

WithoutWithout

WithoutWith

WithWith

WithType

offeedingnil

libitumadlibitumControl-fed

Control-fedad

libitumadlibitumControl-fed

Control-fedLevel

offatLow

HighLow

HighLow

HighLow

HighNo.

of effectivehamsters24

2429

2624

3330

24Incidence

(%)46172835100

9487

96No.

ofadenomas/EAN°0.7

(B)0.2(A)0.5

0.45.3

(D)4.3(D)2.8

(C)4.6 (D)

°EAN, effective animal, x2 test comparisons:, :D(P<0.05).

Table 9 Lesions in hamsters fed diets ad libitum or in controlled protocol"

Ad libitum-fed Control-fed

Lesion

No. of No. ofeffective Incidence effective Incidencehamsters (%) hamsters (%) P

GallbladderhyperplasiaGallbladderinflammationPancreaticlipomatosisPancreaticfibrosisPancreatitis8686IOSIOS1059550439898109109109200331215<0.05<0.05<0.01<0.05<0.001

" Data were pooled across BOP and dietary' fat since these variables did not

significantly influence the results.

ment of colon cancer in rats (16). Similar studies on pancreaticcarcinogenesis have not been reported previously. Our resultssuggest that the enhancement of pancreatic cancer in hamstersfed high-fat diet is due to more than an effect of calorieconsumption.

One difference in the results from mammary and coloncarcinogenesis studies and our investigation on pancreatic carcinogenesis is the length of the studies. The current investigation extended until nearly one-half of the non-carcinogen-treated hamsters had died. As indicated above, the resultssuggest that the pancreatic carcinomas generally developedearlier in the ad libitum-fed hamsters than in the control-fed

groups. In comparison, the studies on mammary and coloncarcinogenesis ended when the dietary fat effect was expectedin the ad libitum-fed groups. Thus, it is possible that cancerwould have developed in the restricted high-fat animals in themammary and colon carcinogenesis studies if the animals hadbeen allowed to live longer.

Also, the hamsters in the present investigation actually weretrained to consume fewer calories, then monitored and held tothat consumption rather than be provided less food than wouldbe consumed by ad libitum animals. In addition, we conductedsimilar training on low-fat and high-fat groups.

This experiment, in contrast to studies on the mammarycarcinogenesis model, noted the absence of a profound influenceof dietary fat or calorie intake on body composition. Theabsence of such an effect in our study may be due to conductingthis measurement only at the end of the experiment. It wouldbe useful to perform the measurement earlier in the experimentto address this issue adequately.

From this experiment and previous experiments on dietaryfat effects on pancreatic carcinogenesis, it appears that high-fat

diets enhanced pancreatic carcinogenesis only in the experiments that used a single dose of 10 or 20 mg BOP/kg bodyweight and were extended for at least 80-90 weeks followingBOP treatment. We observed no influence of dietary fat instudies of the influence of dietary selenium (17) or dried cabbage

(18) in control and high-fat diets in which a dose of 40 mgBOP/kg body weight was used and surviving hamsters werekilled at 40-50 weeks following BOP treatment. The depend

ence of dietary modulation on carcinogen dosage is so oftenobserved that it must be appreciated in designing nutrition andcancer studies.

REFERENCES

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2. Birt, D. F., Stepan, K. R., and Pour, P. M. Interaction of dietary fat andprotein on pancreatic carcinogenesis in Syrian golden hamsters. J. Nati.Cancer Inst., 71: 355-360, 1983.

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4. Reddy, B. S., Wang, C.-X., and Maruyama, H. Effect of restricted caloricintake on azoxymethane-induced colon tumor incidence in male 344 rats.Cancer Res., 47:1226-1228, 1987.

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9. Pour, P., Sayed, G., and Sayed, S. Hyperplastic preneoplastic and neoplasticlesions found in 83 human pancreases. Am. J. Clin. Pathol., 77: 137-152,1982.

10. Munro, H. N., and Fleck, A. Analysis of tissues and body fluids for nitrogenous constituents. In: H. N. Munro (ed.). Mammalian Protein Metabolism,Vol. 3, pp. 423-525. New York: Academic Press, 1969.

11. Ray, A. A. (éd.).SAS Users Guide: Statistics. Cary, NC: SAS Institute, Inc.,1982.

12. Peto, R., Pike, M. C, Day, N. E., Gray, R. G., Lee, P. N., Parish, S., Peto,J., Richards, S., and Wahrendorf, J. Guidelines for simple, sensitive significance tests for carcinogenic effects in long-term animal experiments. In:Long-Term and Short-Term Screening Assays for Carcinogenesis: A CriticalAppraisal, IARC Monograph, Suppl. 2, pp. 301-426. Lyon, France: International Agency for Research on Cancer, 1980.

13. Boissonneault, G. A., Elson, C. E., and Pariza, M. W. Net energy effects ofdietary fat on chemically induced mammary carcinogenesis in F344 rats. J.Nati. Cancer Inst., 76: 335-338, 1986.

14. Forbes, E. B., Swift, R. W., James, W. H., Bratzler, J. W., and Black, A.Further experiments on the relation of fat to economy of food utilization. J.Nutr., 32: 387-396, 1946.

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16. Reddy, B. S., Tanaka, T., and Simi, B. Effect of different levels of dietarytrans fat or corn oil on azoxymethane-induced colon carcinogenesis in F344rats. J. Nail. Cancer Inst., 75: 791-798, 1985.

17. Birt, D. F., Julius, A. D., Runice, C. E., White, L. T., Lawson, T., and Pour,P. M. Enhancement of BOP-induced pancreatic carcinogenesis in selenium-fed Syrian golden hamsters under specific dietary conditions. Nutr. Cancer,//.-21-33, 1988.

18. Bin, D. F., Pelling, J. C., Pour, P. M., Tibbels, M. G., Schweickert, L., andBresnick, E. E.ihanced pancreatic and skin tumorigenesis in cabbage-fedhamsters and mice. Carcinogenesis (Lond.), *: 913-917, 1987.

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1989;49:5848-5851. Cancer Res   Diane F. Birt, Alan D. Julius, Lenora T. White, et al.  

and at a Controlled Calorie Intakead LibitumHigh-Fat Diet Enhancement of Pancreatic Carcinogenesis in Hamsters Fed a

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