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\' . i fw 1'•Le+ Ji Cbpl':n~ ;J Editor's Column L t : Sur. S>nth Path. Res. /. I:3-133(1983) e:91)s K.rW,e (t..i oa3-a387C 63 OOi 1-0i:ss: •s o a`ew• First-Generation Hybrid Syrian Hamster, BIO F1 D Alexander for in vivo Carcinogenesis Bioassay, as a Third Species or to Replace the Mousel F NCrnh:,rger. R.4. .adorns. P Btrnleld. C.G t'on Dongen. E. Solo B.o•Reserrcl Insu:c:e. Cambndge. 'tass . l.'SA Introduction 'The long-term admtntstratton of chemi- cals to'aboratorn animals remains the pr^nct- ;al rre:noJ for deter^tining Mhe:her sub- s;ances are car;inogenic' (S1 Pro:abl~ :he greatest problem is the in- r;re:a:~cn :i resu.:s of c3r::ncger.tc stud:es Mhere :here is no c:car indication of en- ha^,ed tumor Ce%c:e,^rr.ent T`te :arge sari- et% of spen:aneous :~mors found in %erN low to ^:gn ,-cidence ir, redents as the% reach the end of their life-span creates serious pr:bfems of statistical and pathologt- cal e%aluation' (-J The reso1% ing poMer of a lifetime carcino- genesis bioassa~~ to detect the carcinogenic potenc% of a test substance is greatly reduced b~ h:gh spontaneous tumor incidences in the tng test subject. especially in mice. This resolg power could be greatly increased and sharD- encd if a test animal existed free of sponta- neous tumors of the types likely to be tn- duced b% administered carctnogens. Such a This su,d. +as supponed in pan by grants from :ne •at onal Cancer Institute. Nat,onal Institutes of HeaiiR Bethesda. Std Ca-10101. C&,-:+to6 from t!u Fannie E Rippel Foundation. Morristo+n • 1 aed ~rom B-o•Research Consultar.y. Inc Ca?"Dri dge. %1ass laborator.• animal would be especially useful if it were also known to respond to the administration of defined laboratory carcino- gens wtth the formation of tumors in stgntfi- cant numbers. We have descnbed the differential suscep- ttbility of I: inbred S~nan hamster lines (6J to the induction of tumors Ntth dr•erse car- cinogens and ha.e postulated that a carctno- ger,•susceptible inbred hamster ha%tng a low spontaneous tumor incidence could be the :deal test animal for in vivo carcinogenesis bioassa.s. This approach sened well tn c:ga- rette smoke inhalation studtes, since half of the exposed animals of a susceptible inbred line developed respiratory cancer, in contrast to onlv oae of the animals of a less suscepttbte inbred ltne (2, 3). Such inbred hamsters, however, werc relatively short-Itved and therefore not ideally suited for lifetime stud- ies. We h%pothestted that heterosis mtght extend the Itfe span and that crossing two car- ctnogen-suscepttble lines mtght preserve car- cinogen susceptibility We now repon basic information on tumors induced with defined carcinogens in several FI hybnds. also body Metght gatn, food and water consumption and spontaneous tumor formation in one of these. a h~bnd derived from a cross of BIO• IS 16 sires with BIO• 87 :0 dams. This h.- t ~~N O~-~ CT~"88

a i:6 brid is identtfied as the B1O' F1 D Alecander (in honor of Julius .alixander Rippei whose foresight made this work possible). The F I D Alexander not only lives longer than an% other hamster known to us..but displays great susceptibility to administered carcinogens com~ined with low spontaneous tumor inct- dence. Entirely or .•trtually absent from the small array of spontaneous tumors character- istlc of the FI D Alexander are some tumors known to be easily induced by defined car• ctnogens, that is mammary, gastrointestinal. hepatic and pancreatic tumors (6]. Methods T`e paren:a! :nbred ;ires -:ab!e 11. BIO hamsten of our o-n produc::on, -ere sc!ected because the% are -e!I ;haracter rcd (or their survivat. weight pin and ;arunc8en suscepubtin. 161 As in the earlier studies. da:a on :he locil :nduccion o( f brosarcomas by subcu• :ancous i^-ectton of !:-0 6At'.I:•dimeth%lbenzanthra• cene -DkiB 41 ur methvtchotan:hrene NC. Batch 4 : ? I Eas:•nan Ia3akt •n :rcapnlin IBatch :09'. Eas:r"an La;aa/ dcai%c from :!+e study of small gr.u-,s of .o:-.g aG,+;t s•bnds +approitimatcfy 3 ..ar:.Is of a8et pe.%ced to8e:her in Voups of 3-S `am• s:crs per ;age pro•.ded -t1 San-l-Cet Laborator. A n,rna! Bedd:n8: Pa.ion Processin8 Co . Puton. III ), ard :ed xiie:ed Pur,a Lab Chow 5001 tRa:ston P:nna Co St Louis. %to t and tap water ad libitum. D3:a :n :`e rductton of mar^mary cancer den•e from the su,d% of simuartv small groups of .oung adult N>brids stmiIarlv housed and fed, pven %1C in corn oil bt ta%age tsoft rubber French So 8 ca:heterl in di•:ded doses of 4 m8 each. thrce t,mes aweete (or I' consecutt•e +eeks for a total dose of approitmately :00m8 Data on +et&M +ain. sYnwal ind sponta• neous tumor incidence tn the B10 FID AICtander h)bnds denve from two cohons born about I month apan. each consisting of !00 hamsun born within I Weck• Whtch +cre used in IonB-term feeding studtes for the carano8enests bloassay of new chemicals. These FID data result from observations made on the con• vol animals of these swdics Thex studies were con• ducsed in conform:ty with the'Good Laboratory Pnc• Homt.,urEer a,:a-ns 3erri..;. Van CY_•nsen S.•:a Table I. DeCir.ed h%'nnds of inbrcd S~ran ,a-.s:ec stra:ns consiJeceJ susccpub:e or res,s~a:s: to ;.`.c^,:a.. tnduction of tumor H~bnd Inbred parental stra n' destgnauon sire dam' FIA BIO I S Bl0 :`!e FIB BIO I 5 BI0 9' :: FIC BIO I S t6' Pt0 I S FID BIO 15.16 BIO 3' :: FIE BIOB':0 . B10I S FIF BIO87.0 B10 i: :o All inbred bv continuous brother X s:s:er ^a:i:~E for more than 30 consecutt•e genenat:ons S:n:ns BIC IS 16 and 810 81 :0 are considered sus:e;t:t!e. 3:C I. 5 resistant. to tumor induction -tth c.;e:•^.icai Urc:*%• o8ens ttces Retulauons' of t-e l,'n,ted S:a:es Food and D:. idmin:strauon in animal faclfates full% ac:red ted ^ the Amencan Assoc:auon for :he 4ecreG+ut:en c Laboratory An:mal Care IAAALACI ir, t.^.ese s:udie: the hamsters Mere ptaced shonl~ after +ear;-8 a about 6 -eeks of a`et on San•t-Cel bedd:rg :n :r.d...c ual, solid bottom. po!.carbonate ;iascr, :a~}:s Teasr ,rng I I'. X S'. .[ 0 in. eCu:pxd - th sua:ard ;ai lids Imodels 1001' and :.jt:L htj Proau;:s. Ga• Gcld. S 1 1 and »ere fed Pur.^a Ccr..i.ed Lab C•.e SJO: in meal form dispensed in acna,.n:s 8;ass feeder jars musunn8 :: ot tS : c:^ oua:ce e ameter x 8 crn high. Ansei! Brothers. Bos:cn. Mass Each +eek. bod• *ei81t as +e11 as food cor.su^•.e::. -ere measured. -ater cor.r.mpuon -as Cete-rn.nc puanerly All hamsten that died durn8 ene ccu-x cf fced n8 studics. as -ell as the sur•i•ors -n,clk -e sacnficed at the end of :~ears' and a:l harrsen n .- mammary cancer tnducuon stud es that died or .c sacrificed because they v.ere term:nail -ere autopsi and the organs listed in the SCI 8uidel nes for carc:r genesis tests (91 +ere studied htstopat`oiosica.l. = though all hamsters in the fibrosarcoma swd:es -r subjected to detailed gross evaluatton at au:o".. c Ussues Were etamtned hntopatholo8i:.7ilv, w.ith eaceptton of the few tnstances of docbttul Gbroti coma induction that were speclflca!Iy so e4aminec t... f f'ti MN 0"Y' 2 . >f GS

Blo FID Ale:ander Hamsters for in vivo Carcinoaenes!s Bioassay 127 Table 11. Induction o(subcuuncous fibrosarcoma in defined S)nan hamster h~bnds by the local injection of dameth.lbenzanthracene or methylcholanthrene Stnin' Se4 Tumor tnctdencet htem penod. Weeks Iball indeas mean SD DiT t! h~ iM~: ~ nthr]C[rt FIA 1 23 19 2, 3/100 i1 :0 t95 it 14 1 1 3 5 3 0 3 4 FIB ' :9 :4 .91100i1 :5 (961,tt :s 6 :t6 '.0 4 6 F.C .. 6 _. :9540, 1' 04 :a 6 a _ 6 FID . :6 :OllOi.b1 I I) 3: :0:^IiCCit I:o 39 F:E 195>ii 14 _ a 4 tq; %,i ~' 0 9 0 F:F - a,53 e, :a a I , ._:4 J: 8 4 97 100 48 101 93 112 1:6 III 96 '6 43 93 14 F,6 .3S :4 5 F,r _ i:S(:e'a 13. 19 3 3 1 : 9 3 I I 3 9 3 160 30 36 43 t3 FiE •) ::tGit - - ' :F . IB:~1901e1 I'S .3 3 ~ 0 L111 i? 163 06 :9 See :ab;e I •uTOCr of na!nsters with fibrosarcoma total. t :oaa :ndc% = Ii number of tumort a•crage btent period lda>sll x :00 Results F:~rc1Qr:0rra 1n6tGiTron As in pre%ious studies wlth the parental inbred strains (6), D%iB-N proed to be a more potent inducer of subcutaneous Gbro• sarcomas than SiC (table 11). All the tested h%brtds aere about comparable in response to each other and to the susceptible parental stratns, even in those instances in which a susceptible strain had been bred to the resis- tant B1O 1.5. In the MC senes. the hybnd males appeared to be slightly more suscepti- ble to librosarcoma induction than the hy- brid females. wtth the exceptlon of the FIE, the reclprocat cross of the FID Alexander. 4 ~~°#~ #~~~ ~~~~~'>`9 0

a 1:8 Hombur{:r ida!r.s Be^::c'~ ~ir. D.:rSr- _. ~ Tabte 111. Inducuon of inetasustztnj mamman Bland carcinoma in selc::0 h%9nds of ;ena.a Ssn3n hamster strains tail femalcs) Stratn Incidence f Surrtval, weeks: Incidence of met tas st S„n,.a;. ~eeas: pnmarv o carcinoma, mean SD as t rrean Sp FIA 19 20 (95 0ae) :6 6 3:7 15 19 1?9 0°e) :5 9 "~ FIB 14'17 (82 4%) :?.6 S.l I 8 14 157.1~0! 'b~ - - - FIC 12,15 (800%) 26.3 : 49 6f 1:1500°oi :4 ~^---- FID 23::6 (88.S%) :5.2 3 38 '0••'3(8•0ae) • FIE 18:2(818%) `s: 1.92 9•18(S00°v! '30 _ ~ ^ FIF 8,1.(66.%%) 25.6 3 92 5 8 (6:.5 a • ~ Vumber of hamster.s postuve:toul number. Af;er intuat;on of stC Ba••a8e. see test. t 1umtXr of hamsters »ith mtususes (lun8, lymph nodes, or both)•number posm%e While the F IF µas the strain most responstve to fibrosarcoma induction wtth both DMBA and %1C. :`te FID Alecander appcared to be among the group of hvbnd strains regarded as somcwhat more susceptible than the oth- ers to the tnJucuon of i;brosarcomas. tJJn7•r1r1' G ,-^d CJr:7-0ntJ A1u of the h.bnd scratns appeared to be about as susceptible as an% of the prevtously examined suscepttble parental strains (6) to the chemtcal ,nductton of mammary gland tumors, htstologtcall. t~pe B adenocarctno- mas or paptllary c>stadenocarctnomas, as in earlier studies I 11. µ htle the F l D responded onl% margtnaliv better than three of the hy- bnds• the most responstve was the FIA. cu- rtously• not the reciprocal of the FID (ta• ble III). On the other hand, the FI D had the highest incidence of inetastases• mostly to the lymph nodes and the lungs as in the previous studies wtth the parental strains (IJ. The presence of these histologically confirmed metastases did not appear to be associated with a shonentng of the survtval ttme. Bod}• It'etg..: G..:r. Sar.. _. ;I CorlSurnptrOn c:r.,r FC-~d C: -... . .:`~: . . the FlD .a/e.t'arcer The data from onlv one of the rAo e\ar-• tned btRh cohorts are presented t:t since the data from the second cohort afe tuallysupertmposable -ksno:c_1:ns-:ra:e3r- IterstudteswtthpurebredS~•f:aa'a^s::rs .... h5brtd females tended to be '.g-.:ef :^ ae.i^t than the males until about S-, acc~s ~i :lze At this time they becamc and ~c• matned so until the onset of grad::a. y tth stnescer,;e.:o r~ e-: decline associated tng at about 65-'0 Meeks of age. whe.^. ae:g-7 differences between the se\ es ter.Ce~ come obscured. This pcnod c' ~::::nt^ :e ~s. crac Metght was characterized b% more Meek-to-Meek fluctuation in mcan bec wetght than was e1tdent prior to ;!as t:r•.e : Average water consumption Kas obser% to be uniformly higher among tr.e 'er•.:a: than among the males. Mtth perceptthi. It vanabtltty. After the attainment of peak bc weight, around 25 weeks of age. water cc sumption averaged about 15-! 6 ml da• c "~"~' M~~ ~~ ~" ~ ~ 1

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a Table I%'. Mru W:~i.ust• A:._• ),-r vr.a^s ;. .^e --:> a NonrrCop!~ttri r..e;. . _~. Krdno -_-tuDular ,:r:a:atran lntr _ _ _ ian% cna:~e _ _ , sac %ia:es frr..a.eti :e~on I c^hon : ;crer, i - _ JA1 n 17 n % n Ll ' r. S S' S 96 do s3 491 30. 333 43 494 _ _ thrombosts ~ _ Hean' ' - 3 '6 e 2 • S' 8 _ Colon_. cecum h%pcrplasra. c~s:!c :9 !33' 3,37 8 _ pol.p - - -•-- ._ 46 . s . S _5 6 _ -acute rnflammat on - LunB-- -- _ _ 7 !0 11 1:` _ _ chronrc rnflammauo_n- _ _ `i .3 i i~ _ __ focl sdnomats_s 7 e o _ 3 3 3 a:rophv Tcstes 49 56 3 46 SI.I _ _ Th~rord c.st 2 2.3 c>st O•an _ atrophi Paxras 4 46 1 il _ c%st 3 3 + _I 1 I a mlordos s 4 4 6 3 ) 3 _ ir,eru:s 1fJ..qnu~f Nnn. ~S phoma _ L•m 16 Ib j _ 6 b' _ iJrenal cortrcal ;3rc•noma I 1:6 12 13 3 §~rtor-.13~- . - _ ` 3 ` 0 Colon or cecum aoenocarcrnoma L'ter,ne:arc-nora Paurealrc caroro ra $alr.an ~:~n~ :arc:noma I II ~1e_anorr.~ Slomacn ~dc-oc~rc.^. ma Hepatoma BM.en r •mvs ijrcnai adeno.T.a and n,7e'plisH 33319 L•Tpn no.u 1e^ar8roma I II Spleen hemansroma `3 SILrn heman8,ons Pa_ncreas (,slet ccll adenoma a&J Prtatlsn adenoma n.per-ptas.alt-- - 5 S' T_hecoma Lcrom.oma rulehner' Sair%ar) (land adenoma . :3 Hrsuoc>toma 1 11 Krdne% idenomaa hamanoma Hsmanoms bile ducr 2 _'3 lung SGuamous cell paprlloma. (orttomach tie, us 4 44 ' 22 3 33 1 fl j -- '8 3= : ~ :- 10 li 5 d 9: _-' _ 4 16 ! 4 : I 1 1-_ -- ~- - S 5' 3 3A . I .. I 11 s :') ~, , CTR NN 04d2 2

M i Bio FID Ale><ander Hamsters for in vtvo Carcmogenests Bioassay the females and 12-15 ml day for the males. Dramatic increases in water consumption began to take place at about 62 weeks of age in the females and somewhat later, at about 74 weeks of age, in the males and this in- crease was associated with commencement of the generalized decline and marked fluc- tuation in body weight already noted. The mean daily water intake peaked at about 30 ml-day at 82 Meeks of age among the females and at about ac?--15 ml da> at 9G- 100 weeks of age among the males. a daily intake corresponding to almost =000 of the body welght among the females and 30°,0 among the males. %khtle no measurements of unnarv output Mere made, the ph%slcal evidence of larger than normal amounts of urine in the cage during this period of %astl% ,ncreased water consumption suggests that intense dturests ma% be an Imponant source of the bod> Aeight tluctuatton that occurs at chls time Despite the remarkable changes in body weight that occurred dunng the penod of Meight loss associated Ntth agetrg and de- spite the important increases in water con- sumptton noted during that pertod, food con- sumpuon remained Mtthin the range of 8- 10 g•da~ wrtci, ,-3 a T,vrmat characteristic of adults in peak condition. Food consumption of both sexes earlier dunng the period of active growth, was consistently within the range of'-9 & day. Hisropathology The fibrosarcomas induced in these FI hybrids by single subcutaneous injections of DMBA or MC, as well as the mammary gland carcinomas induced by the repeated gavage of MC in corn oll, were essentially like those induced by these means in the parental strains (6J. The detailed histopathology of the Fl D.Alexander, in panicular, summarized in table IV, den.es from hamsters dying spon- taneously during the course of the study. with the exceptlon that the last 20% of sur.ivors were sacnficed within the course of I week. the females at about I'*i •ears of age. the males at a little over 2.ears (see above, and f;g. :). Stoderate to severe renal tubular dila- tation. c~suc changes in the Itver, cardiac t!trombosts. and cysuc h.perplasta in the cc- cum and the colon Mere the commonest non- neoplasttc findtngs. the FID hybnds being no different from their parental strains in these regards. Am%lotdosts, frequently involving multiple sttes, most commonly spleen. It.er and kidney, was more prevalent in the fe- males than the males of both senes. though it appeared to be present in an incidence in the females of cohort I which was nearly 3 times that of the females of cohort 2. The incidence of adrenal hyperplasta. adrenal adenoma and adrenal carcinoma together was, on the whole, higher in males than in females, as was the incidence of lymohoma. As to neoplasms. adrenal tumors were the ' Includes one sarcoma of the jaw. one of the pentoneum. two of the skin, one of the cecum. an endometnal stromal sarcoma and a hemangiosarcoma of the It% er - Incsudes one adenocarctnoma of the endocer.t.. in addit1on, one sQuamous cell carcinoma of the ccrvti t 4 Also. one pancreatic adenoma Inot tslet Celll Also one endomctnal pol.p CTR ) i ) j 042217134

v 9 0 t . 1): 7o ~ 60 so. 40 a 0.«~.~.....«w i0C 00000 •. O •«.«. ., Hcm=u,;: A,,i3.r.s 3er-. ~e',: % . D -;e )... «.«... ••. ~. .e . 0 0 0 SS 60 6S 70 'S 50 65 90 9s 'GO Aq.. .e.• s Fig. 2. Normal sun~i.at in 90 male FID Aleun- der nams:.rs -i and in '40 female FID Akunder h]msters ':t most commonlv found in these FI D h.bnds. especially among the males. The htstopatho- logic distinction betMeen adrenal adenoma and carcinoma is not sharp. It was noted. hoMever, that metastasizing adrenal tumors Nere large (o-.er 2 cm in diameter). had nu- mcrous mttoses. often necrosis and nuclear pleomorphism. Tumors with any of these features Mere called carcinoma. In the con- text of this defintuon, about one third of the tumors fulfilling the above criteria metasta- sized to distant sites. With one exception. all the adenocarctno- mas of the endometnum were noninvasive or superficially invasive tumors. Lymphomas. either lymphocyttc or histiocytic. were, in most cases. quite extensive. involving multi- ple organs. Discussion "5 ri---'-. These data re%eal the %anous de::ne: F; h.bnds to be about c:r^part!e Al:^ :3:, other and Mtth their suscepttott ,ar:n:a: strains in their suscepubtltt~- :o :rie :^.cr^-:a1 induction of fibrosarcoma o: mam--ar,• gland carcinoma. e%en in those :nstacccs tn which the FI h.brtd %4as den.ed from a cress between a susceptible parental st^atn and :ne resistant 81O 1.5 parental strain. Based u;Jn thts. the choice of the FI D Alexander - thc cross between the BIO 15 16 male and the BIO 87.:0 female - as the test subject mos; suited for long-term btoassay programs Mas to a certatn extent arbttrary, except that this particular hybnd derives from a cross be• tween parental strains both of Nhtc't are deemed to be susceptible to chemical :r.duc- tton of tumor. This background in fact T.a,. have conferred the slight advantage the F: D seemed to have over the others in respon- L.r 7<m R f f N 04 .. •i7a-.lt

0 Bio FI D Alexander Hamsters for in vivo Carcmo6enests Bioassay siveness. especially as regards the induction of fibrosarcomas in both sexes with D`tBA and in females with MC. or as regards the induction of metastasizing mammary gland carcinoma with MC. A practical and eco- nomic consideration from the animal pro- duction point of view, leading to the ultimate selection of the F1 D as the test subject of choice for long-term bioassays, was the fact that the males of the parental BIO 8'.20 strain are notoriously tnfertile. but the large and gentle f*males of this istratn make excel- lent dams. These studies also re•eal the FI DAlexan- der to have had an exceptionally long sur- vival for S}rian hamsters kept in the labora• torv under the stated condtttons. aiso %ctght gain and peak size comparable to or better than that of the larger of the tNo parental slralns. and an extraordrnanly attractl%e spontaneous tumor profile. In contrast to mice and many strains of rats. only two neo• plasms (I%mphoma and adrenal corllcal car• ctnoma) are significant in incidence in the F I D Alexander. neither of these of the types most readily induced by chemical carcino- gens B,. contrast, tumors such as mammary gland carcinoma and hepatoma. of high natu- ral incidence in other laboratory species, are of low spontaneous occurrence in the FID Alcxander and its parental inbred stratns. Khtle they are nevenheless readily inducible v,tth the appropriate carcinogen. These features combine to make the FID Alexander the most useful among our cur- rently avatlable genetically defined Syrian hamster strains for long-term studies such as lifetime carcinogenesis bioassays. We antici- pate that as Syrian hamsters continue to gain µtde appltcatlon in such studies, the FID •Mexander v4tll come to find an tmponant place in them. References 133 I Adams. R.A.; Homburger. F.; Russfield. A B. Soto. E.: 4lethylcholanthrene•lnduced metastattc mammary carcinoma in several inbred hamster strains. Prog. eap. Tumor Res.. vol. 21• pp. •08- s13 (Karler. Basel 1979). 2 Bernfeld. P.; Homburger. F.; Russfield. A.B.. Strain diferences in the response of inbred Svnan hamsters to crgarene smoke rnhalat,on. J. nain Cancer Inst. S! I I41-1IS7 (19'4). 3 Bernfeld. P. Homburger. F. Soto. E. Pat. K J Cigarette smoke inhalation studies tn inbred S>• rian golden hamsters. J nain Cancer Inst 6J 6'S- 669 (1979). 4 Golbcr8. L.. Carnno8enesis testing of chemicals (CRC Press. Cleveland 19'4). S Hombureer. F . Adams. R A . Soto. E.. Van DonB• cn. C G. Susceptib ht. and resistance to chemical ;3:cino{ens in inbred S~nan hamsters Prot . ezp. T;:mor kes - vol :4, pp :1 S-::1 1 KarBer. Basel ;c-91 6 Homburler. F . Hsuc1 S S. Kerr. C S Russfield. A B Inncnted susceptibilit) of inbred stra ns of S•nan hamster to induction of subcutaneous sar• coma and mammar. and gastrointestinal carci• noma b. subcutaneous and 8astnc administration ofpol.nuclearhvdrocarbons Cancer Res J: 360- 366 (I97:). 7 Intera8ency Liaison Group. work Group on Risk Assnsment. Scientific bases for identification of potential carcinogens and estimation of risks J. natn Cancer Inst 6i 241-:68 (1971) 1NauonatZoucoto8y tro8ram. fucal Yesr 1942. -lnnual Plan NTP•81•9s. March 1982 (Research Triangle Park. N C ). 9 SontuB. M M.. PaBe. N P . Saffiottt. U Guidelines for carctnogeneus bioassay in small rodents (Car- ctno8enesis Division of Cancer Cause and Prc- •enuon, National Cancer Institute. Bethesda 19'S) 10 United States Food and Drug Administration: Sonchnial laboratory studies. Good laboratory pracuces regulations Federal Register. December ::. 19'8. pp 59986-600:5 F HOmburgcr \1D. Bio•Rescarcn Insiiiuu 9 Commcrc,al A.cnue Carnbr C{e %1A J:tal ILSAI CTR PIN 042 ';r 1=1 6 -