N,N-dimethyl-p-toluidine

Carcinogenicity

Description of key information

There was clear evidence of carcinogenic activity of the test chemical in male F344/N rats based on increased incidences of hepatocellular carcinoma, and hepatocellular adenoma or carcinoma (combined), and increased incidences of nasal cavity neoplasms (primarily nasal cavity transitional epithelium adenoma). The increased incidences of thyroid gland follicular cell neoplasms may have been related to treatment. There was clear evidence of carcinogenic activity of the test chemical in female F344/N rats based on increased incidences of hepatocellular carcinoma and hepatocellular adenoma or carcinoma (combined). The occurrence of nasal cavity transitional epithelium adenoma was considered to be related to treatment.The occurrence of thyroid gland follicular cell neoplasms in male rats may have been related to treatment. The incidence of thyroid gland follicular cell adenoma was increased at the 60 mg/kg dose, and in addition, two thyroid gland follicular cell carcinomas occurred in the 60 mg/kg group. The incidence of follicular cell adenoma or carcinoma (combined) in the 60 mg/kg group exceeded the historical control ranges for corn oil gavage studies and for all routes of exposure.The occurrence of nasal cavity transitional epithelium adenoma in female rats was considered to be related to treatment because these are rare neoplasms that have not occurred in the concurrent vehicle controls or in corn oil gavage historical controls and have occurred in only one of 1,196 historical control animals by all routes of exposure.The occurrence of thyroid gland follicular cell neoplasms in male rats may have been related to treatment. The incidence of thyroid gland follicular cell adenoma was increased at the 60 mg/kg dose, and in addition, two thyroid gland follicular cell carcinomas occurred in the 60 mg/kg group. The incidence of follicular cell adenoma or carcinoma (combined) in the 60 mg/kg group exceeded the historical control ranges for corn oil gavage studies and for all routes of exposure.. Based on these effects, the test chemical can be carcinogenic in nature. Hence, the LOAEL value for the test chemical can be considered to be 6mg/kg/day

Key value for chemical safety assessment

Carcinogenicity: via oral route

Link to relevant study records

Reference

Endpoint:

carcinogenicity: oral

Type of information:

experimental study

Adequacy of study:

key study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

data from handbook or collection of data

Justification for type of information:

data is from peer reviewed journals

Qualifier:

according to guideline

Guideline:

other: as mentioned below

Principles of method if other than guideline:

The toxicity potential of the test chemical was evaluated in a chronic oral toxicity study in rats.

GLP compliance:

not specified

Species:

rat

Strain:

Fischer 344

Sex:

male/female

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: Taconic Farms, Inc. (Germantown, NY)
- Females (if applicable) nulliparous and non-pregnant: [yes/no]
- Age at study initiation: Rats were 5 to 7 weeks old at the beginning of the studies.
- Weight at study initiation:
- Fasting period before study:
- Housing: Male rats were housed up to three per cage, female rats were housed five per cage,
1. Cages : Polycarbonate (Lab Products, Inc., Seaford, DE), changed weekly (male mice) or twice w
eekly
2. Bedding: Irradiated Sani-Chips (P.J. Murphy Forest Products Corp., Montville, NY), changed
weekly (male mice) or twice weekly
3. Cage Filters: Spun-bonded polyester (Snow Filtration Co., Cincinnati, OH), changed every 2 weeks
4. Racks: Stainless steel (Lab Products, Seaford, DE), changed and rotated every 2 weeks
- Diet (e.g. ad libitum): Irradiated NTP-2000 wafer feed (Zeigler Brothers, Inc., Gardners, PA), av
ailable ad libitum, changed weekly
- Water (e.g. ad libitum): Tap water (Columbus municipal supply) via automatic watering system (Edst
rom Industries, Waterford, WI), available ad libitum
- Acclimation period: Animals were quarantined for 13 (male rats), 14 (female rats),
DETAILS OF FOOD AND WATER QUALITY:
ENVIRONMENTAL CONDITIONS
- Temperature (°C): 72° ± 3° F
- Humidity (%): 50% ± 15%
- Air changes (per hr): 10/hour
- Photoperiod (hrs dark / hrs light): 12 hours/day
IN-LIFE DATES: From:Rats: October 20 (males) or 21 (females), 2004 To:Rats: October 17 (males) or 19 (females), 2006

Route of administration:

oral: gavage

Vehicle:

corn oil

Details on exposure:

Details on oral exposure
PREPARATION OF DOSING SOLUTIONS: Dose formulations were prepared by adding the appropriate
amount of the test chemical to corn oil to achieve the desired concentration. Dose for-mulations
were prepared three times for the 3-month studies.The 400 mg/mL dose formulation was prepared
and observed to be a true solution, therefore, no homoge-neity or gavageability studies were perfo
rmed. Stability studies of a 1.0 mg/mL formulation in corn oil were performed using GC/FID. Stabili
ty was confirmed for up to 44 days for formulations stored in amber glass containers sealed with
Teflon®-lined lids, protected from light, at up to room temperature and for at least 3 hours under si
mulated animal room conditions.
DIET PREPARATION
- Rate of preparation of diet (frequency): No data available
- Mixing appropriate amounts with (Type of food): No data available
- Storage temperature of food: No data available
VEHICLE
- Justification for use and choice of vehicle (if other than water): The test chemical dissolved in corn
oil
- Concentration in vehicle: 0, 6, 20, or 60 mg/kg
- Amount of vehicle (if gavage): 2.5 mL/kg
- Lot/batch no. (if required): No data available

Analytical verification of doses or concentrations:

yes

Details on analytical verification of doses or concentrations:

Periodic analyses of the dose formulations were con-ducted by the study laboratory using GC/FID. During the 2-year studies, the dose formulations were analyzed at least every 3 months; animal room
samples were also analyzed.Of the dose formulations analyzed and used, all 30 for rats were within 10% of the target concentrations; all 12 animal room samples for rats were within 10% of the target
concentrations.

Duration of treatment / exposure:

2 years

Frequency of treatment:

5 days/week for 104 (male rats) or 105 weeks

Remarks:

0, 6, 20, or 60 mg/kg

No. of animals per sex per dose:

Groups of 50 male and 50 female rats

Control animals:

yes, concurrent vehicle

Details on study design:

- Dose selection rationale: Based on mortality in the 1,000 mg/kg groups, decreased (more than
10%) final mean body weights in the 125, 250, and 500 mg/kg male groups, and treatment-related
nonneoplastic lesions in the liver, nose, spleen, kidney, and bone mar-row with increased severity
at 125 mg/kg or greater, a high dose of 60 mg/kg test chemical was selected for the 2-year gavage
study in rats. The low dose of 6 mg/kg was selected because this dose was reported to cause toxicity
in humans (Potter et al., 1988). The doses selected for the 2-year gavage study in rats were 0, 6, 20,
and 60 mg/kg, with a threefold dose spacing.
- Rationale for animal assignment (if not random): Animals were distributed randomly into groups of
approximately equal initial mean body weights.
- Fasting period before blood sampling for clinical biochemistry:
- Rationale for selecting satellite groups:
- Post-exposure recovery period in satellite groups:
- Section schedule rationale (if not random):
- Other:

Observations and examinations performed and frequency:

Observations and examinations performed & frequency
CAGE SIDE OBSERVATIONS: Yes
- Time schedule: twice daily
- Cage side observations checked in table [No.?] were included: Survival was observed.
DETAILED CLINICAL OBSERVATIONS: Yes
- Time schedule:Daily, clinical findings were recorded every 4 weeks beginning with week 5 and at the end of the studies
BODY WEIGHT: Yes
- Time schedule for examinations: core study animals were weighed initially, weekly for the first 13 weeks, every 4 weeks thereafter, and at the end of the studies
FOOD CONSUMPTION AND COMPOUND INTAKE (if feeding study): No data available
- Food consumption for each animal determined and mean daily diet consumption calculated as g food/kg body weight/day: No data available
- Compound intake calculated as time-weighted averages from the consumption and body weight gain data: No data available
FOOD EFFICIENCY:No data available
- Body weight gain in kg/food consumption in kg per unit time X 100 calculated as time-weighted averages from the consumption and body weight gain data: No data available
WATER CONSUMPTION AND COMPOUND INTAKE (if drinking water study): No data available
- Time schedule for examinations: No data available
OPHTHALMOSCOPIC EXAMINATION: No data available
- Time schedule for examinations: No data available
- Dose groups that were examined: No data available
HAEMATOLOGY: Yes / No / Not specified: yes
- Time schedule for collection of blood:Blood was collected from the retroorbital sinus of clinical
pathology rats on day 86 for hematology.
- Anaesthetic used for blood collection: Yes (identity) / No / Not specified
- Animals fasted: Yes / No / Not specified
- How many animals:
- Parameters checked in table [No.?] were examined.: Hematology: hematocrit; hemoglobin and methemoglobin concentrations; erythrocyte, reticulocyte, platelet, and Heinz body counts; mean cell
volume; mean cell hemoglobin; mean cell hemoglobin concentration; and leukocyte count and differentials
CLINICAL CHEMISTRY: No data available
Time schedule for collection of blood: No data available
- Animals fasted: No data available
- How many animals: No data available
- Parameters checked in table [No.?] were examined. No data available
URINALYSIS: No data available
- Time schedule for collection of urine: No data available
- Metabolism cages used for collection of urine: No data available
- Animals fasted: No data available
- Parameters checked in table [No.?] were examined. No data available
NEUROBEHAVIOURAL EXAMINATION: No data available
- Time schedule for examinations:No data available
- Dose groups that were examined: No data available
- Battery of functions tested: sensory activity / grip strength / motor activity / other: No data available

Sacrifice and pathology:

Animals were sacrifice using Carbon dioxide asphyxiation
GROSS PATHOLOGY: Yes
Necropsies were performed on all core study animals.At necropsy, all organs and tissues were examined for grossly visible lesions, and all major tissues were fixed and pre-served in 10% neutral
buffered formalin (except eyes were first fixed in Davidson’s solution), processed and trimmed, embedded in paraffin, sectioned to a thickness of 4 to 6 μm, and stained with hematoxylin and eosin for microscopic examination. For all paired organs (e.g., adrenal gland, kidney, ovary), samples fromeach organ were examined.
HISTOPATHOLOGY:
Complete histopathology was performed on all core study animals. In addition to gross lesions and tissue masses, the following tissues were examined: adrenal gland, bone (including marrow), brain,
clitoral gland, esophagus, eye, gallbladder (mice), Harderian gland, heart (including aorta), large intestine (cecum, colon, and rectum), small intestine (duodenum, jejunum, and ileum), kidney, liver, lung (and mainstem bronchi), lymph nodes (mandibular and mesenteric), mammary gland, nose, ovary, pancreas, parathyroid gland, pituitary gland, preputial gland, prostate gland, salivary gland, sk
in, spleen, stomach (forestomach and glandular), testis (with epididymis and seminal vesicle), thymus, thyroid gland, trachea, urinary bladder, uterus, and Zymbal’s gland (male rats).

Statistics:

Survival Analyses: Analysis of survival was estimated by the product-limit procedure of Kaplan and Meier . Statistical analyses for possible dose related effects on survival were analyzed by useing Cox’s
method for testing two groups for equality and Tarone’s life table test to identify dose related trends.All reported P values for the survival analyses are two sided.Shirley and Dunn. Jonckheere’s test was
used to analyszed by the significance of the dose related trends and to determine whether a trend sensitive test (Williams’ or Shirley’s test) was more appropriate for pairwise comparisons than a test
that does not assume a monotonic dose related trend (Dunnett’s or Dunn’s test).

Clinical signs:

effects observed, treatment-related

Description (incidence and severity):

Clinical findings included signs of pallor in 60 mg/kg females and hyper-activity and boxing behavior in 20 mg/kg females and 60 mg/kg males and females. Hyperactivity and boxing behavior were first
noticed during study month 8. All animals exhibited normal behavior prior to dosing. Boxing behavior, characterized by “kangaroo boxing” between cage mate pairs, was seen after dosing in 20 mg/kg females and 60 mg/kg males and females. In most months where this behavior was observed, the percentage of animals displaying this behavior was greater following the first dose of the week compared
to the percentage following the last dose of the week. The percentage of 60 mg/kg females displaying boxing behavior decreased over the course of the study.

Dermal irritation (if dermal study):

not specified

Mortality:

mortality observed, treatment-related

Description (incidence):

Survival of 60 mg/kg males was significantly less than that of the vehicle controls. Although the survival of 60 mg/kg females was decreased compared to the vehicle controls, the decrease was not statistically significant

Body weight and weight changes:

effects observed, treatment-related

Description (incidence and severity):

The mean body weights of 60 mg/kg males were over 10% less than those of the vehicle controls after week 61 (day 421) and those of 60 mg/kg females were less than those of the vehicle controls
after week 33 (day 225)

Food consumption and compound intake (if feeding study):

not specified

Food efficiency:

not specified

Water consumption and compound intake (if drinking water study):

not specified

Ophthalmological findings:

not specified

Haematological findings:

effects observed, treatment-related

Description (incidence and severity):

The hematology findings in this 3-month interim evaluation were consistent with what occurred in the 3-month study. Increases in methemoglobin and Heinz bodies occurred in the 20 and 60 mg/kg male and female groups. Dose-related decreases occurred in the erythron characterized by decreases in hematocrit values, hemoglobin concentrations, and erythrocyte counts in the 20 and 60 mg/kgmale and female groups. The erythron decreases were accompanied by trends toward erythrocyte macrocytosis and hypochro-mia evidenced by increases in the mean cell volume and decreases in the mean cell hemoglobin concentration values, respectively. Increases in reticulocyte counts demonstrated increased erythropoiesis in response to the decreased erythron. While the magnitude of the eryth-ron decreases were not sufficient to categorically clas-sify these as anemias, the patterns of erythron changes were identical to what occurred in the 3-month study. At most, minimally decreased hemoglobin concentrations (decreased <5%), increased methemoglobin values (increased
<20% in males only), and increased Heinz bodies (increased in females only) occurred in the 6 mg/kg groups.

Clinical biochemistry findings:

not specified

Urinalysis findings:

not specified

Behaviour (functional findings):

not specified

Immunological findings:

not specified

Organ weight findings including organ / body weight ratios:

not specified

Gross pathological findings:

not specified

Neuropathological findings:

not specified

Histopathological findings: non-neoplastic:

effects observed, treatment-related

Description (incidence and severity):

Administration of the test chemical resulted in increased incidences of nonneoplastic lesions of the liver and nasal cavity in male and female rats and the mesenteric lymph node in male rats and the
kidney in male and female rats; the spleen and bone marrow in male and female rats

Histopathological findings: neoplastic:

effects observed, treatment-related

Description (incidence and severity):

There was clear evidence of carcinogenic activity of the test chemical in male F344/N rats based on increased incidences of hepatocellular carcinoma, and hepatocellular adenoma or carcinoma (combined), and increased incidences of nasal cavity neoplasms (primarily nasal cavity transitional epithelium adenoma). The increased incidences of thyroid gland follicular cell neoplasms may have been related to treatment. There was clear evidence of carcinogenic activity of the test chemical in female F344/N rats based on increased incidences of hepatocellular carcinoma and hepatocellular adenoma or carcinoma (combined). The occurrence of nasal cavity transitional epithelium adenoma was considered to be related to treatment.The occurrence of thyroid gland follicular cell neoplasms in male rats may have been related to treatment. The incidence of thyroid gland follicular cell adenoma was increased at the 60 mg/kg dose, and in addition, two thyroid gland follicular cell carcinomas occurred in the 60 mg/kg group. The incidence of follicular cell adenoma or carcinoma (combined) in the 60 mg/kg group exceeded the historical control ranges for corn oil gavage studies and for all routes of exposure.The occurrence of nasal cavity transitional epithelium adenoma in female rats was considered to be related to treatment because these are rare neoplasms that have not occurred in the concurrent vehicle controls or in corn oil gavage historical controls and have occurred in only one of 1,196 historical control animals by all routes of exposure.The occurrence of thyroid gland follicular cell neoplasms in male rats may have been related to treatment. The incidence of thyroid gland follicular cell adenoma was increased at the 60 mg/kg dose, and in addition, two thyroid gland follicular cell carcinomas occurred in the 60 mg/kg group. The incidence of follicular cell adenoma or carcinoma (combined) in the 60 mg/kg group exceeded the historical control ranges for corn oil gavage studies and for all routes of exposure.

Other effects:

not specified

Dose descriptor:

LOAEL

Effect level:

6 mg/kg bw/day (nominal)

Based on:

test mat.

Sex:

male/female

Basis for effect level:

body weight and weight gain

clinical signs

haematology

histopathology: neoplastic

histopathology: non-neoplastic

mortality

Critical effects observed:

yes

Lowest effective dose / conc.:

6 mg/kg bw/day (nominal)

System:

hepatobiliary

Organ:

liver

nasal cavity

Treatment related:

yes

Dose response relationship:

yes

Relevant for humans:

not specified

Conclusions:

There was clear evidence of carcinogenic activity of the test chemical in male F344/N rats based on increased incidences of hepatocellular carcinoma, and hepatocellular adenoma or carcinoma (combined), and increased incidences of nasal cavity neoplasms (primarily nasal cavity transitional epithelium adenoma). The increased incidences of thyroid gland follicular cell neoplasms may have been related to treatment. There was clear evidence of carcinogenic activity of the test chemical in female F344/N rats based on increased incidences of hepatocellular carcinoma and hepatocellular adenoma or carcinoma (combined). The occurrence of nasal cavity transitional epithelium adenoma was considered to be related to treatment.The occurrence of thyroid gland follicular cell neoplasms in male rats may have been related to treatment. The incidence of thyroid gland follicular cell adenoma was increased at the 60 mg/kg dose, and in addition, two thyroid gland follicular cell carcinomas occurred in the 60 mg/kg group. The incidence of follicular cell adenoma or carcinoma (combined) in the 60 mg/kg group exceeded the historical control ranges for corn oil gavage studies and for all routes of exposure.The occurrence of nasal cavity transitional epithelium adenoma in female rats was considered to be related to treatment because these are rare neoplasms that have not occurred in the concurrent vehicle controls or in corn oil gavage historical controls and have occurred in only one of 1,196 historical control animals by all routes of exposure.The occurrence of thyroid gland follicular cell neoplasms in male rats may have been related to treatment. The incidence of thyroid gland follicular cell adenoma was increased at the 60 mg/kg dose, and in addition, two thyroid gland follicular cell carcinomas occurred in the 60 mg/kg group. The incidence of follicular cell adenoma or carcinoma (combined) in the 60 mg/kg group exceeded the historical control ranges for corn oil gavage studies and for all routes of exposure.. Based on these effects, the test chemical can be carcinogenic in nature. Hence, the LOAEL value for the test chemical can be considered to be 6mg/kg/day

Executive summary:

The toxicity potential of the test chemical was evaluated in a chronic oral toxicity study in rats.Groups of 50 male and 50 female Fischer 344 rats were administered 0, 6, 20, or 60 mg /kg body weight of test chemical in corn oil by gavage, 5 days per week for 104 or 105 weeks. Additional groups of 10 male and 10 female rats (clinical pathology study) were administered the same doses for 86 days. Survival of 60 mg/kg males was significantly less than that of the vehicle controls. Mean body weights of 60 mg/kg males and females were more than 10% less than those of the vehicle controls after week 61 and week 33, respectively. Clinical findings included signs of pallor in 60 mg/kg females and hyperactivity and boxing behavior in 20mg/kg females and 60 mg/kg males and females. In the 20 and 60 mg/kg groups, there were dose-related decreases in hematocrit values, hemoglobin concentrations, and erythrocyte counts. There were similar trends toward erythrocyte macrocytosis and hypochromia and increased erythropoiesis as seen in the 3-month study. While the magnitudes of the erythron decreases were not sufficient to classify the responses as anemias, the patterns of the erythron changes were identical to those in the 3-month study. In the liver of 60 mg/kg males and females, there were significantly increased incidences of hepatocellular carcinoma and hepatocellular adenoma or hepatocellular carcinoma (combined). Numerous nonneoplastic liver lesions occurred in dosed males and females primarily in the 20 and 60 mg/kg groups. In the nose, there were significantly increased incidences of transitional epithelium adenoma and transitional epithelium adenoma or carcinoma (combined) in 60 mg/kg males; transitional epithelium adenoma also occurred in female rats administered 6 or 60 mg/kg. In the nose, there were significantly increased incidences of nonneoplastic lesions in the olfactory, respiratory, and transitional epithelia of dosed rats. These lesions occurred with the greatest incidence and severity in the 60 mg/kg groups. The incidences of inflammation and nerve atrophy were significantly increased in males and females administered 60 mg/kg.

There was clear evidence of carcinogenic activity of the test chemical in male F344/N rats based on increased incidences of hepatocellular carcinoma, and hepatocellular adenoma or carcinoma (combined), and increased incidences of nasal cavity neoplasms (primarily nasal cavity transitional epithelium adenoma). The increased incidences of thyroid gland follicular cell neoplasms may have been related to treatment. There was clear evidence of carcinogenic activity of the test chemical in female F344/N rats based on increased incidences of hepatocellular carcinoma and hepatocellular adenoma or carcinoma (combined). The occurrence of nasal cavity transitional epithelium adenoma was considered to be related to treatment.The occurrence of thyroid gland follicular cell neoplasms in male rats may have been related to treatment. The incidence of thyroid gland follicular cell adenoma was increased at the 60 mg/kg dose, and in addition, two thyroid gland follicular cell carcinomas occurred in the 60 mg/kg group. The incidence of follicular cell adenoma or carcinoma (combined) in the 60 mg/kg group exceeded the historical control ranges for corn oil gavage studies and for all routes of exposure.The occurrence of nasal cavity transitional epithelium adenoma in female rats was considered to be related to treatment because these are rare neoplasms that have not occurred in the concurrent vehicle controls or in corn oil gavage historical controls and have occurred in only one of 1,196 historical control animals by all routes of exposure.The occurrence of thyroid gland follicular cell neoplasms in male rats may have been related to treatment. The incidence of thyroid gland follicular cell adenoma was increased at the 60 mg/kg dose, and in addition, two thyroid gland follicular cell carcinomas occurred in the 60 mg/kg group. The incidence of follicular cell adenoma or carcinoma (combined) in the 60 mg/kg group exceeded the historical control ranges for corn oil gavage studies and for all routes of exposure.. Based on these effects, the test chemical can be carcinogenic in nature. Hence, the LOAEL value for the test chemical can be considered to be 6mg/kg/day

Endpoint conclusion

Endpoint conclusion:

adverse effect observed

Dose descriptor:

LOAEL

6 mg/kg bw/day

Study duration:

chronic

Species:

rat

Quality of whole database:

Klimisch Rating 2

System:

hepatobiliary

Organ:

liver

nasal cavity

Carcinogenicity: via inhalation route

Endpoint conclusion

Endpoint conclusion:

no study available

Carcinogenicity: via dermal route

Endpoint conclusion

Endpoint conclusion:

no study available

Justification for classification or non-classification

Under the conditions of these 2-year oral gavage studies, there was clear evidence of carcinogenic activity in male as well as female Fischer 344 rats and B6C3F1 mice. Since there is enough evidence on the carcinogenic activity caused by the test chemical, hence it can be classified under the category “Carc 1B”

 

Additional information

Various studies have been reviewed to evaluate the carcinogenic potential of the test chemical. These include in vivo experimental studies performed on rats as well as mice for the test chemical. The results are mentioned below:

The toxicity potential of the test chemical was evaluated in a chronic oral toxicity study in rats. Groups of 50 male and 50 female Fischer 344 rats were administered 0, 6, 20, or 60 mg /kg body weight of test chemical in corn oil by gavage, 5 days per week for 104 or 105 weeks. Additional groups of 10 male and 10 female rats (clinical pathology study) were administered the same doses for 86 days. Survival of 60 mg/kg males was significantly less than that of the vehicle controls. Mean body weights of 60 mg/kg males and females were more than 10% less than those of the vehicle controls after week 61 and week 33, respectively. Clinical findings included signs of pallor in 60 mg/kg females and hyperactivity and boxing behavior in 20mg/kg females and 60 mg/kg males and females. In the 20 and 60 mg/kg groups, there were dose-related decreases in hematocrit values, hemoglobin concentrations, and erythrocyte counts. There were similar trends toward erythrocyte macrocytosis and hypochromia and increased erythropoiesis as seen in the 3-month study. While the magnitudes of the erythron decreases were not sufficient to classify the responses as anemias, the patterns of the erythron changes were identical to those in the 3-month study. In the liver of 60 mg/kg males and females, there were significantly increased incidences of hepatocellular carcinoma and hepatocellular adenoma or hepatocellular carcinoma (combined). Numerous nonneoplastic liver lesions occurred in dosed males and females primarily in the 20 and 60 mg/kg groups. In the nose, there were significantly increased incidences of transitional epithelium adenoma and transitional epithelium adenoma or carcinoma (combined) in 60 mg/kg males; transitional epithelium adenoma also occurred in female rats administered 6 or 60 mg/kg. In the nose, there were significantly increased incidences of nonneoplastic lesions in the olfactory, respiratory, and transitional epithelia of dosed rats. These lesions occurred with the greatest incidence and severity in the 60 mg/kg groups. The incidences of inflammation and nerve atrophy were significantly increased in males and females administered 60 mg/kg.

There was clear evidence of carcinogenic activity of the test chemical in male F344/N rats based on increased incidences of hepatocellular carcinoma, and hepatocellular adenoma or carcinoma (combined), and increased incidences of nasal cavity neoplasms (primarily nasal cavity transitional epithelium adenoma). The increased incidences of thyroid gland follicular cell neoplasms may have been related to treatment. There was clear evidence of carcinogenic activity of the test chemical in female F344/N rats based on increased incidences of hepatocellular carcinoma and hepatocellular adenoma or carcinoma (combined). The occurrence of nasal cavity transitional epithelium adenoma was considered to be related to treatment.The occurrence of thyroid gland follicular cell neoplasms in male rats may have been related to treatment. The incidence of thyroid gland follicular cell adenoma was increased at the 60 mg/kg dose, and in addition, two thyroid gland follicular cell carcinomas occurred in the 60 mg/kg group. The incidence of follicular cell adenoma or carcinoma (combined) in the 60 mg/kg group exceeded the historical control ranges for corn oil gavage studies and for all routes of exposure.The occurrence of nasal cavity transitional epithelium adenoma in female rats was considered to be related to treatment because these are rare neoplasms that have not occurred in the concurrent vehicle controls or in corn oil gavage historical controls and have occurred in only one of 1,196 historical control animals by all routes of exposure.The occurrence of thyroid gland follicular cell neoplasms in male rats may have been related to treatment. The incidence of thyroid gland follicular cell adenoma was increased at the 60 mg/kg dose, and in addition, two thyroid gland follicular cell carcinomas occurred in the 60 mg/kg group. The incidence of follicular cell adenoma or carcinoma (combined) in the 60 mg/kg group exceeded the historical control ranges for corn oil gavage studies and for all routes of exposure.. Based on these effects, the test chemical can be carcinogenic in nature. Hence, the LOAEL value for the test chemical can be considered to be 6mg/kg/day

This result is supported by a similar study performed in mice. Groups of 50 male and 50 female B6C3F1 mice were administered 0, 6, 20, or 60 mg/kg body weight of the test chemical in corn oil by gavage, 5 days per week for 105 weeks.Survival of 60 mg/kg females was significantly less than that of the vehicle control group. Mean body weights of 60 mg/kg males and females were more than 10% less than those of the vehicle controls after week 89 and week 65, respectively. In the liver, there were significantly increased incidences of hepatocellular adenoma in 20 and 60 mg/kg females and hepatocellular carcinoma in 60 mg/kg males and all dosed female groups. The increased incidences of hepatocellular adenoma and carcinoma in the dosed groups were primarily due to increased incidences of animals with multiple hepatocellular neoplasms. The incidences of hepatoblastoma were significantly increased in 20 mg/kg males and 60 mg/kg males and females. In all dosed groups of males and females, there were significantly increased incidences of hepatocyte hypertrophy, and the incidences of eosinophilic focus were significantly increased in the 20 and 60 mg/ kg males and females. There were significantly increased incidences of fatty change and necrosis in 60 mg/kg females.In the lung of 20 and 60 mg/kg female mice, there were significantly increased incidences of alveolar/ bronchiolar adenoma and alveolar/bronchiolar adenoma or carcinoma (combined). There were also significantly increased incidences of alveolar epithelium hyperplasia in 20 mg/kg females; bronchiolar epithelium regeneration, bronchus epithelium regeneration, and bronchus necrosis in 60 mg/kg females; and alveolar infiltrates of histiocytes in 60 mg/kg males and females.In the forestomach of 20 and 60 mg/kg female mice, there were significantly increased incidences of squamous cell papilloma and squamous cell papilloma or carcinoma (combined). There were significantly increased incidences of epithelium hyperplasia in 20 and 60 mg/kg females, and inflammation and ulcer in 60 mg/kg females. In the nose, there were significantly increased incidences of nonneoplastic lesions of the olfactory and respiratory epithelia in 60 mg/kg males and 20 and 60 mg/kg females. There were significantly increased incidences of nerve atrophy in 60 mg/kg males and females and of inflammation in 60 mg/kg females. The incidences of atrophy of the olfactory lobe were significantly increased in 60 mg/kg males and females. In 60 mg/kg females, the incidences of regenerative hyperplasia of the nasolacrimal duct and necrosis of the vomeronasal organ were significantly increased. In the spleen, there was a significantly increased incidence of atrophy in 60 mg/kg females. There were also significantly increased incidences of bone marrow hyperplasia in all dosed groups of females and mesenteric lymph node atrophy in 60mg/kg females. Based on the carcinogenic evidence observed in both male and female mice, hence the test chemical can be considered to be carcinogenic in nature and the LOAEL value can be considered to be 20 mg/kg/day.

Under the conditions of these 2-year oral gavage studies, there was clear evidence of carcinogenic activity in male as well as female Fischer 344 rats and B6C3F1 mice. Since there is enough evidence on the carcinogenic activity caused by the test chemical, hence it can be classified under the category “Carc 1B”