Rodent tumors of questionable relevance to man

Xenobiotic-induced Rodent Tumors of Questionable

Relevance to Human Cancer Risk

R. R. [email protected]

Photomicrographs courtesy of the National Toxicology Program (http://ntp.niehs.nih.gov)

Rodent Tumors of Questionable Relevance

Rodent-Specific Mode of Action• Renal tumors secondary to α-2u-

globulin nephropathy• Urinary bladder tumors secondary

to irritation• Mesovarian leiomyomas

secondary to β2 receptor agonists• Carcinoids secondary to H2

antagonists• Thyroid follicular tumors • Uterine endometrial carcinoma

secondary to dopamine agonists• Leydig cell tumors in rats

secondary to hormonal perturbations

Tumors in Unique Rodent Tissues• Harderian Gland• Preputial Gland• Clitoral Gland• Zymbal’s Gland• Forestomach

Α-2u globulin nephropathyProposed key events

Chemical exposure and binding to α-2u globulinAccumulation of the bound α-2u in renal tubular

epithelial cellsCytotoxicity to renal tubular epithelial cellsCompensatory renal tubular cell proliferationDevelopment of renal tumors

Α-2u globulin nephropathy

Renal Tubular Adenoma

Α-2u globulin nephropathy• Animals affected

– Mature male rat under influence of testosterone produces large amount of α-2u globulin

• Xenobiotics associated with α-2u globulin nephropathy– JP-4 & other jet fuels hexachloroethane– Isophorone d-limonene– Parachlorobenzene Pentachloroethane– Unleaded gasolineNitrotoluene

• Unaffected mammals– Female rats Male and female mice Humans– Male NCI-Black-Reiter rat

Urinary Bladder Tumors

• Secondary to irritation– Mechanical irritation from foreign bodies or calculi

• Affects rats and mice– Threshold effect – only seen at doses of chemical

that produce calculi• Agents associated with urinary bladder tumors

– Uracil Cyclamate – Chronic irritation

Urinary Bladder Papilloma

Mesovarian Leiomyomas in Rats• Seen following administration of β2-receptor

adrenergic stimulants– Proliferation of mesovarian smooth muscle– Propanolol (adrenergic blocker) prevents formation of

this tumor• Xenobiotics causing this effect

Salbutamol Terbutaline• Specific to the rat

– Not seen in mice or hamsters– Not seen in humans with long history of using β2-

stimulants

Carcinoids (Neuroendocrine Tumors) in the Rodent Stomach

• Associated with prolonged blockage of acid secretion– Seen for powerful and long-lasting H2-receptor antagonists

& proton-pump inhibitors given at high doses– SK&F93479 Omeprazole Butachlor Methyleugenol

• Leads to increased gastrin levels– Stimulation of neuroendocrine cells leading to hyperplasia

and neoplasia– Slight hypergastrinemia in humans not associated with

hyperplasia or neoplasia of neuroendocrine cells• Seen at high doses in rodents

– Humans have low serum gastrin levels (margin of safety)

Neuroendocrine Tumor(Carcinoid)

Thyroid Follicular Cell Neoplasms• Caused by altered feedback mechanism resulting in

prolonged stimulation of the thyroid by TSH• Rats vs. humans lack high-affinity thyroxin-binding globulin,

are more sensitive to inhibition of thyroid peroxidase, are more sensitive to hepatic enzyme induction

• Categories of altered feedback mechanism– Interference with iodine uptake & thyroid hormone synthesis or

secretion• sulfonamides

– Interference with metabolism of T4 or T3• FD&C Red No. 3 (erythrosine)

– Increased metabolism & excretion of thyroid hormones• Phenobarbital Polychlorinated biphenyls

Thyroid Follicular Adenoma

Uterine Endometrial Carcinomas in Rats

• Seen in older rats associated with estrogen dominance

• Permanent estrus and endometrial stimulation– Leads to endometrial carcinoma

• Seen in rats treated with dopamine agonists– Bromocriptine

• Similar endocrine imbalance does not occur in women

Uterine Endometrial Carcinoma

Leydig Cell Tumors in Rats

• Interference with Leydig cell control mechanisms (7 different types of interference)

• All involve the hypothalamic-pituitary-testis axis• Xenobiotics associated with rat Leydig cell tumors

– Cimetidine Finasteride Flutamide– Gembibrozil Indomethacin DEHP

• Rats vs humans– Rats have 14 times more LH receptors– LHRH receptors unique to the rat

Leydig Cell Tumor

Rodent Tumors of Questionable Relevance

Rodent-Specific Mode of Action• Renal tumors secondary to α-2u-

globulin nephropathy• Urinary bladder tumors secondary

to irritation• Mesovarian leiomyomas

secondary to β2 receptor agonists• Carcinoids secondary to H2

antagonists• Thyroid follicular tumors • Uterine endometrial carcinoma

secondary to dopamine agonists• Leydig cell tumors in rats

secondary to hormonal perturbations

Tumors in Unique Rodent Tissues• Harderian Gland• Preputial Gland• Clitoral Gland• Zymbal’s Gland• Forestomach

2-Year Oncogenicity Studies Evaluated

Pesticide database (www.epa.gov/ncct/toxrefdb/)

257 Rat246 Mouse281 Total Rodent1006 Sex/Species

National Toxicology Program database (http://ntp.niehs.nih.gov/)

552 Total Rodent ~2200 Sex/Species

http://www.epa.gov/ncct/toxrefdb/

http://ntp.niehs.nih.gov/

Pesticide Database

One study (1 of 281) has an increased incidence of Harderian gland tumors in female mice and forestomach tumors in male and female mice.

No other sex/species exposure groups in the 280 other 2-year oncogenicity studies had increased incidences of these rodent only tumors.

NTP database

90 of the 552 studies available for review had increased incidence of at least one of the list of 5 rodent unique tissue tumors in at least one sex/species.

NTP DatabaseForestomachFemale rat 20; Male rat 24; Female mouse 34; Male mouse 29

Zymbal’s glandFemale rat 19; Male rat 22; Female mouse 4; Male mouse 3

Harderian glandMale rat 1; Female mouse 15; Male mouse 16

Preputial gland Clitoral glandMale rat 13; Male mouse 5 Female rat 16

NTP Database

In 11 cases there was an increased incidence of a single rodent specific tumor in a single sex/species as the only positive neoplastic finding.

Female rat: Clitoral gland 2; Zymbal’s gland 1

Male rat: Forestomach 1; Preputial gland 1

Female mouse: Forestomach 4

Male mouse: Forestomach 1

(90/552 positive studies)

Harderian glandDescribed by Johann Jacob Harder in 1694

Present in terrestrial vertebrates – amphibians to mammals

In mammals – not present in cattle, horses, carnivores, higher primates including humans

Functional activities include (depending on species) – lubrication, immune response, pheromone production, saliva, osmoregulation, photoreception, thermoregulation, elaboration of growth factors.

Has been shown to possess metabolic capability – Cytochrome P450, lipid metabolism, and porphyrin metabolism

Female mice15 positive studiesIn one case the only tumor in study.9/15 involved genotoxic xenobiotics including the study with only positive tumor site

Male mice16 positive studiesIn one case the only tumor in study9/16 involved genotoxic xenobiotics including the study with only positive tumor site

In the only tumor site cases in mice, both sexes had Harderian gland tumors.

Male ratSingle study with Harderian gland tumor, multi-site genotoxic carcinogen.

Harderian Gland Tumor

Harderian Gland Adenoma

Effect of Diet on Spontaneous Harderian Gland Tumors

NIH-07 overall incidence


Female mouse

129/32863.9%

183/144812.6%

Male mouse

175/32865.3%

223/139915.9%

Male rat

1/32450.03%

1/13990.07%

Harderian Gland

• Multifunctional gland• Metabolically active• Spontaneous incidence influenced by diet• Tumors typically seen in studies where other

tumors are associated with treatment• Humans do not have Harderian glands

Clitoral glandPreputial gland

Paired Specialized sebaceous glands

Preputial Gland Tumors in NTP Studies

Male mice5 positive studiesAll are multisite carcinogens4/5 are genotoxic3/5 also had Zymbal’s gland tumors

4/5 had skin and/or Zymbal’s gland tumors

Male rat13 positive studies2 studies the only tumor in male rat, 1 case only tumor in study5/13 are genotoxic5/11 also had Zymbal’s gland tumors4/11 had skin tumors


Female rat16 positive studies in NTP database11/16 were genotoxic4 studies only tumor in female rat,

2 cases only tumor in study9/12 also had Zymbal’s gland tumors5/12 also had skin tumors


2/4 were positive in male rat preputial gland

Clitoral Gland Tumors in NTP Studies

Clitoral glandPreputial gland



Male mouse

0/35290%

2/13940.1%

Male rat

274/33488.2%

70/13955.0%



Female rat

359/325911.0%

161/134712.0%

Preputial and Clitoral Glands

• Specialized sebaceous glands

• Typically associated with other cutaneous tumors

• In 7 studies both rat preputial (7/13) and clitoral (7/16) gland tumors were present.

• Spontaneous tumor rates not affected by diet.

• Not present in humans.

Zymbal’s gland

Modified sebaceous glands along the base of the ear.Possess cytochrome P450 metabolizing enzymes.May be deficient in some phase II metabolizing enzymes

http://www.item.fraunhofer.de/reni

Mouse Zymbal’s gland Mouse skin sebaceous gland

Zymbal’s Gland Tumors NTP Mouse Studies

Female mouse4 positive studies all multisite carcinogens2/4 were genotoxic carcinogens

Male mouse3 positive studies all multisite carcinogensAll positive for preputial gland2/3 were genotoxic carcinogens

Zymbal’s Gland Tumors NTP Rat Studies

Female rat19 studies positive 14/19 were genotoxic carcinogens3 were the only female rat tumor in study6/16 also had skin tumors9/16 also had clitoral gland tumors

10/16 had clitoral gland and/or skin tumorsMale rat

22 studies positive 16/22 were genotoxic carcinogens2 were the only male rat tumor in study16/20 also had skin tumors5/16 also had preputial gland tumors

16/16 had preputial gland and/or skin tumors

Zymbal’s Gland Carcinoma

Incidence of Zymbal’s gland tumors in Control RodentsFed NIH-07 Diet

NTP database

Derm acetone

Derm ethanol

Derm Gavage corn oil

Gavage methyl cellulose

Gavage water

Inhalation Feed Water Total and %

Female Rat

1/100 2/301 0/51 1/401 0/100 0/50 6/1052 6/1001 5/330 21/33860.6%

Male Rat

1/100 4/302 0/50 2/402 1/101 0/50 15/1055 10/1004 6/331 39/33951.2%

Female Mouse

0/150 0/302 nd 26/463

5.6%0/100 0/51 1/1077 0/953 0/340 26/3436

0.7%

Male Mouse

0/150 0/299 nd 23/464

5.0%0/100 0/50 0/1074 0/952 0/340 24/3429

0.7%

Incidence of Zymbal’s gland tumors in Control RodentsFed NIH-2000 Diet

NTP database

Derm ethanol

Gavage corn oil


Gavage water


Female Rat

0/150 1/150 0/100 0/150 4/350 1/250 2/200 8/1350

Male Rat

1/150 2/150 0/100 0/150 2/349 4/300 2/200 11/1399

Female Mouse

0/150 0/148 0/100 0/150 0/400 1/300 0/200 1/1448

Male Mouse

0/150 0/150 0/100 0/150 0/400 0/250 0/199 0/1399

FM5.6%MM5.0%

Zymbal’s Gland Tumors

• Modified sebaceous gland

• Typically associated with other cutaneous tumors

• Metabolically active site

• Majority associated with genotoxic carcinogens

• Decreased diet-related spontaneous tumor rates in mice

Forestomach Papilloma

Forestomach Tumors in NTP Mouse StudiesFemale mouse

35 studies positive (from 90/552 studies) 22/35 genetox positive17/35 irritants28/35 genotoxic or irritant16 only female mouse tumor

13/16 genetox positive or irritant

Male mouse30 studies positive 20/30 genetox positive16/30 irritants25/30 genotoxic or irritant8 only male mouse tumor

8/8 genetox positive or irritant

Female rat20 studies positive (from 90/552 studies) 15/20 genetox positive10/20 irritants16/20 genotoxic and/or irritant9 only female rat tumor

8/9 genotoxic or irritant

Male rat24 studies positive 18/24 genetox positive11/24 irritants21/24 genotoxic and/or irritant9 only male rat tumor

8/9 genotoxic or irritant

Forestomach Tumors in NTP Rat Studies

Forestomach Tumors by Route of Administration

Female mouse21/35 Gavage studies

18/21 corn oil 3/21 water

7/35 Feed

Male mouse19/30 Gavage studies

15/19 corn oil 3/19 water1/19 methyl cellulose

5/30 Feed

Female rat15/20 Gavage studies

10/15 corn oil 4/15 water1/15 methyl cellulose

4/20 Feed

Male rat15/24 Gavage studies

11/15 corn oil 4/15 water

8/24 Feed

Incidence of Forestomach tumors in Control RodentsFed NIH-07 Diet

NTP database

Derm acetone

Derm ethanol

Derm Gavage corn oil


Gavage water


Female Rat

0/100 0/301 0/51 2/401 0/100 0/50 1/1052 2/1001 1/330 6/33860.2%

Male Rat

1/100 0/302 2/50 2/402 0/101 0/50 1/1055 0/1004 0/331 6/33950.2%

Female Mouse

2/1501.3%

2/2990.6%

nd 19/463

4.1%1/1001.0%

0/510%

10/10770.9%

16/9531.7%

5/3401.5%

55/34331.6%

Male Mouse

2/1501.3%

6/3022.0%

nd 22/464

4.7%0/1000%

0/500%

7/10740.7%

14/9521.5%

4/3401.2%

55/34321.6%

Incidence of Forestomach tumors in Control RodentsFed 2000 Diet

NTP database

Derm ethanol

Gavage corn oil


Gavage water


Female Rat

0/150 1/150 1/100 1/150 0/350 1/250 1/200 5/13500.4%

Male Rat

2/150 0/150 0/100 0/150 0/349 0/300 1/200 3/13990.2%

Female Mouse

3/1502.0%

4/148

2.7%1/1001.0%

3/1502.0%

6/4001.5%

5/3001.7%

3/2001.5%

25/14481.7%

Male Mouse

1/150 1/150

0.7%2/100 3/150 4/400 4/250 3/199 18/1399

1.3%

FM4.1%MM4.7%

Forestomach Tumors• Susceptible to local combination of chronic wounding (irritation)

and mutagenicity

• More likely to develop from direct exposure; more likely in gavage studies

• Metabolically active site

• Decreased diet-related spontaneous tumor rate in mice

• In 8/9 and 9/9 cases of only tumor in male or female rats, respectively, also tumor in opposite sex.

• In 7/8 and 12/16 cases of only tumor in male or female mice, respectively, also tumor in opposite sex.

Site Concordance

Target organ concordance need not be a prerequisite for evaluating the implications of animal study results for humans.

There is evidence that growth control mechanisms at the level of the cell are homologous among mammals, but these mechanisms are not necessarily site concordant.

Site Concordance

Target organ concordance need not be a prerequisite for evaluating the implications of animal study results for humans.

There is evidence that growth control mechanisms at the level of the cell are homologous among mammals, but these mechanisms are not necessarily site concordant.

Tumors in Unique Rodent Tissues

• Harderian Gland• Preputial Gland• Clitoral Gland• Zymbal’s Gland• Forestomach

Concerns about the significanceof these to human cancer riskcan be addressed using the mode of action/human relevanceframework approach.

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Rodent Cancer Study Databases

Pesticide database (www.epa.gov/ncct/toxrefdb/) National Toxicology Program database (http://ntp.niehs.nih.gov/)

http://www.epa.gov/ncct/toxrefdb/

http://ntp.niehs.nih.gov/

Rodent tumors of questionable relevance to man

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