Some species-specific rat and mouse tumor responses seen in cancer bioassays that are not relevant to human health risk include alpha-2u globulin induced renal cancer, urinary bladder tumors, carcinoids secondary to blockage of gastric acid secretion, various endocrine tumors, forestomach tumors, Zymbal’s gland tumors, preputial and clitoral gland tumors and Harderian gland tumors.

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Rodent tumors of questionable relevance to man

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Index of Slides

1. Xenobiotic-induced Rodent Tumors of Questionable Relevance to Human Cancer Risk R. R. Maronpot Maronpot@me.com Photomicrographs courtesy of the National Toxicology Program (http://ntp.niehs.nih.gov)
2. 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
3. Α-2u globulin nephropathy Proposed key events Chemical exposure and binding to α-2u globulin – Accumulation of the bound α-2u in renal tubular epithelial cells – Cytotoxicity to renal tubular epithelial cells – Compensatory renal tubular cell proliferation – Development of renal tumors
4. Α-2u globulin nephropathy
5. Renal Tubular Adenoma
6. 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 gasoline Nitrotoluene • Unaffected mammals – Female rats Male and female mice Humans – Male NCI-Black-Reiter rat
7. 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
8. Urinary Bladder Papilloma
9. 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
10. 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)
11. Neuroendocrine Tumor (Carcinoid)
12. 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
13. Thyroid Follicular Adenoma
14. 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
15. Uterine Endometrial Carcinoma
16. 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
17. Leydig Cell Tumor
18. 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
19. 2-Year Oncogenicity Studies Evaluated Pesticide database (www.epa.gov/ncct/toxrefdb/) 257 Rat 246 Mouse 281 Total Rodent 1006 Sex/Species National Toxicology Program database (http://ntp.niehs.nih.gov/) 552 Total Rodent ~2200 Sex/Species
20. 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.
21. 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.
22. NTP Database Forestomach Female rat 20; Male rat 24; Female mouse 34; Male mouse 29 Zymbal’s gland Female rat 19; Male rat 22; Female mouse 4; Male mouse 3 Harderian gland Male rat 1; Female mouse 15; Male mouse 16 Preputial gland Clitoral gland Male rat 13; Male mouse 5 Female rat 16
23. 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)
24. Harderian gland Described 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
25. Female mice 15 positive studies In one case the only tumor in study. 9/15 involved genotoxic xenobiotics including the study with only positive tumor site Male mice 16 positive studies In one case the only tumor in study 9/16 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 rat Single study with Harderian gland tumor, multi-site genotoxic carcinogen. Harderian Gland Tumor
26. Harderian Gland Adenoma
27. Effect of Diet on Spontaneous Harderian Gland Tumors NIH-07 overall incidence NIH-2000 overall incidence Female mouse 129/3286 3.9% 183/1448 12.6% Male mouse 175/3286 5.3% 223/1399 15.9% Male rat 1/3245 0.03% 1/1399 0.07%
28. 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
29. Clitoral glandPreputial gland Paired Specialized sebaceous glands
30. Preputial Gland Tumors in NTP Studies Male mice 5 positive studies All are multisite carcinogens 4/5 are genotoxic 3/5 also had Zymbal’s gland tumors 4/5 had skin and/or Zymbal’s gland tumors Male rat 13 positive studies 2 studies the only tumor in male rat, 1 case only tumor in study 5/13 are genotoxic 5/11 also had Zymbal’s gland tumors 4/11 had skin tumors 5/11 had skin and/or Zymbal’s gland tumors
31. Female rat 16 positive studies in NTP database 11/16 were genotoxic 4 studies only tumor in female rat, 2 cases only tumor in study 9/12 also had Zymbal’s gland tumors 5/12 also had skin tumors 10/12 had skin and/or Zymbal’s gland tumors 2/4 were positive in male rat preputial gland Clitoral Gland Tumors in NTP Studies
32. Clitoral glandPreputial gland NIH-07 overall incidence NIH-2000 overall incidence Male mouse 0/3529 0% 2/1394 0.1% Male rat 274/3348 8.2% 70/1395 5.0% NIH-07 overall incidence NIH-2000 overall incidence Female rat 359/3259 11.0% 161/1347 12.0%
33. 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.
34. 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
35. Mouse Zymbal’s gland Mouse skin sebaceous gland
36. Zymbal’s Gland Tumors NTP Mouse Studies Female mouse 4 positive studies all multisite carcinogens 2/4 were genotoxic carcinogens Male mouse 3 positive studies all multisite carcinogens All positive for preputial gland 2/3 were genotoxic carcinogens
37. Zymbal’s Gland Tumors NTP Rat Studies Female rat 19 studies positive 14/19 were genotoxic carcinogens 3 were the only female rat tumor in study 6/16 also had skin tumors 9/16 also had clitoral gland tumors 10/16 had clitoral gland and/or skin tumors Male rat 22 studies positive 16/22 were genotoxic carcinogens 2 were the only male rat tumor in study 16/20 also had skin tumors 5/16 also had preputial gland tumors 16/16 had preputial gland and/or skin tumors
38. Zymbal’s Gland Carcinoma
39. Incidence of Zymbal’s gland tumors in Control Rodents Fed 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 21/3386 0.6% Male Rat 1/100 4/302 0/50 2/402 1/101 0/50 15/1055 10/1004 6/331 39/3395 1.2% 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%
40. Incidence of Zymbal’s gland tumors in Control Rodents Fed NIH-2000 Diet NTP database Derm ethanol Gavage corn oil Gavage methyl cellulose Gavage water Inhalation Feed Water Total and % 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 FM 5.6% MM 5.0%
41. 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
42. Forestomach Papilloma
43. Forestomach Tumors in NTP Mouse Studies Female mouse 35 studies positive (from 90/552 studies) 22/35 genetox positive 17/35 irritants 28/35 genotoxic or irritant 16 only female mouse tumor 13/16 genetox positive or irritant Male mouse 30 studies positive 20/30 genetox positive 16/30 irritants 25/30 genotoxic or irritant 8 only male mouse tumor 8/8 genetox positive or irritant
44. Female rat 20 studies positive (from 90/552 studies) 15/20 genetox positive 10/20 irritants 16/20 genotoxic and/or irritant 9 only female rat tumor 8/9 genotoxic or irritant Male rat 24 studies positive 18/24 genetox positive 11/24 irritants 21/24 genotoxic and/or irritant 9 only male rat tumor 8/9 genotoxic or irritant Forestomach Tumors in NTP Rat Studies
45. Forestomach Tumors by Route of Administration Female mouse 21/35 Gavage studies 18/21 corn oil 3/21 water 7/35 Feed Male mouse 19/30 Gavage studies 15/19 corn oil 3/19 water 1/19 methyl cellulose 5/30 Feed Female rat 15/20 Gavage studies 10/15 corn oil 4/15 water 1/15 methyl cellulose 4/20 Feed Male rat 15/24 Gavage studies 11/15 corn oil 4/15 water 8/24 Feed
46. Incidence of Forestomach tumors in Control Rodents Fed 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 0/100 0/301 0/51 2/401 0/100 0/50 1/1052 2/1001 1/330 6/3386 0.2% Male Rat 1/100 0/302 2/50 2/402 0/101 0/50 1/1055 0/1004 0/331 6/3395 0.2% Female Mouse 2/150 1.3% 2/299 0.6% nd 19/463 4.1% 1/100 1.0% 0/51 0% 10/1077 0.9% 16/953 1.7% 5/340 1.5% 55/3433 1.6% Male Mouse 2/150 1.3% 6/302 2.0% nd 22/464 4.7% 0/100 0% 0/50 0% 7/1074 0.7% 14/952 1.5% 4/340 1.2% 55/3432 1.6%
47. Incidence of Forestomach tumors in Control Rodents Fed 2000 Diet NTP database Derm ethanol Gavage corn oil Gavage methyl cellulose Gavage water Inhalation Feed Water Total and % Female Rat 0/150 1/150 1/100 1/150 0/350 1/250 1/200 5/1350 0.4% Male Rat 2/150 0/150 0/100 0/150 0/349 0/300 1/200 3/1399 0.2% Female Mouse 3/150 2.0% 4/148 2.7% 1/100 1.0% 3/150 2.0% 6/400 1.5% 5/300 1.7% 3/200 1.5% 25/1448 1.7% Male Mouse 1/150 1/150 0.7% 2/100 3/150 4/400 4/250 3/199 18/1399 1.3% FM 4.1% MM 4.7%
48. 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.
49. 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.
50. 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 significance of these to human cancer risk can be addressed using the mode of action/human relevance framework approach. <
51. Rodent Cancer Study Databases Pesticide database (www.epa.gov/ncct/toxrefdb/) National Toxicology Program database (http://ntp.niehs.nih.gov/)