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Description of key information

Carcinogenicity NOAEL 0.5 % in diet (non-guideline study).

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
Study period:
No data
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: Meets generally accepted scientific standards, well documented and acceptable for assessment
Reason / purpose:
reference to same study
Qualifier:
no guideline followed
Deviations:
not applicable
Principles of method if other than guideline:
3 concentrations of test material were fed to 96 rats over a 2 year period. At mortality (either natural or at end of study), pathological examinations were made for tumours.
GLP compliance:
no
Species:
rat
Strain:
Wistar
Sex:
male/female
Details on test animals and environmental conditions:
TEST ANIMALS
- Source: A. Tuck & Son, Battlesbridge, Essex, United Kingdom
- Age at study initiation: No data
- Weight at study initiation: males mean weight 81 g; females mean weight 77 g.
- Fasting period before study: No data
- Housing: Grid floor metal cages, 4 animals per cage
- Diet: ad libitum
- Water: ad libitum
- Acclimation period: No data

ENVIRONMENTAL CONDITIONS
- Temperature (°C): 20 °C ± 2 °C
- Humidity (%): No data
- Air changes (per hr): Not quantified, but described as "ventilated".
- Photoperiod (hrs dark / hrs light): No data
Route of administration:
oral: feed
Vehicle:
unchanged (no vehicle)
Details on exposure:
DIET PREPARATION
- Rate of preparation of diet (frequency): No data
- Mixing appropriate amounts with: Reground Spratt's Laboratory Animal Diet No. 1
- Storage temperature of food: No data
Analytical verification of doses or concentrations:
not specified
Duration of treatment / exposure:
104 wks
Frequency of treatment:
Continuous - test substance included in ad libitum diet.
Post exposure period:
None
Remarks:
Doses / Concentrations:
0.02 %
Basis:
nominal in diet
Remarks:
Doses / Concentrations:
0.1 %
Basis:
nominal in diet
Remarks:
Doses / Concentrations:
0.5 %
Basis:
nominal in diet
No. of animals per sex per dose:
48 animals per sex per dose
Control animals:
yes, concurrent no treatment
yes, historical
Details on study design:
- Dose selection rationale: Based on previously published academic papers.
Positive control:
None
Observations and examinations performed and frequency:
OTHER OBSERVATIONS
- Not relevant to this endpoint; see repeat dose toxicity section for details.
Sacrifice and pathology:
MORTALITY
- Animals were found dead or were euthanised in extremis.
- Animals were euthanised after 104 wks if they had not already died.

PATHOLOGY
- Pathological examinations were made for tumours
- Other observations made but not relevant to this endpoint; see repeat dose toxicity section for details.
Histopathological findings: neoplastic:
no effects observed
Details on results:
MORTALITY
- Mortality in the study is shown in Table 1 in the attached supporting materials.
- Between 12 and 24 animals in each group out of a total of 48 in each group made it to sacrifice at the end of the study
- The mortality was not significantly higher in any test group than in the corresponding control group and there was no dose-response relationship at P < 0.05

HISTOPATHOLOGY: NEOPLASTIC
- See table 9 in the attached supporting materials

Most of the tumours were encountered as isolated findings or in very low incidence in any one group with no statistically-valid differences between the treated and control groups. The exceptions to this were interstitial cell tumours of the testis, which occurred more frequently in the males given 0.02 % or 0.5 % test material, and pituitary adenomata, which were more common amongst females of the same groups that in the controls. In both cases, the incidence in the intermediate group did not differ significantly from the control group.

A number of malignant tumours of vascular origin were seen. Two haemangiosarcomata were present in female animals, one in the 0.1 % group and the other in the 0.5 % group. In males, similar tumours were found in single animals from the control and two lowest dose groups. In addition, haemangioendotheliomata were identified in one female in the 0.5 % group (in the liver) and in one in the 0.02 % group (in the uterus). Benign tumours of vascular origin (haemangiomata) were confined to one control male and 0.1 % dose female.

Lymphosarcomata were encountered in occasional animals in most groups. Affected were the spleen of a control male and multiple organs, including the lymph nodes, of a single male in each of the groups fed 0.02 % and 0.1 % test material. In females, lymphosarcomata were identified in the thyrus of two rats from the 0.02 % dose group and in the bone of one in the 0.5 % dose group. Two male animals, one from 0.02 % dose and one from the 0.1 % dose group had reticulum cell sarcomata.

Some malignant tumours of common origin were found in more than one treated animal. An osteosarcoma occurred in one male from the 0.02 % group and in one from the 0.5 % group, the tumour in the latter case being identified from a metastatic deposit in the lung. Spindle cell sarcoma was found in the large intestine of one male fed 0.5 % test material and in the bladder of a male fed 0.02 % and adrenal-gland cortical carcinomata occurred in 2 males (in the 0.02 % and 0.5 % groups). In females, mammary adenocarcinoma was found in 1 animal from each of the 2 higher dosage groups.

Single occurrences of malignant tumours in treated animals without a similar control finding included a uterine endometrial sarcoma and neurofibrosarcoma of the ovary in animals fed 0.5 % and 0.1 % test material respectively, while an astrocytoma was present in the brain of a male animal fed 0.1 % test material. An anaplastic carcinoma of the pancreas and basal-cell carcinoma of the skin were found in males from the high dose group.

There were more pituitary adenomata in the treated female rats than in the controls but Dunnington et al. considered such tumours to be particularly common in old rats and cite incidences of 50-70 % that have frequently been reported. They also reported that similar incidences 50-70 % have been reported in their laboratory in control animals. They thus considered the number seen in the treated animals as not unusual, and the difference in incidence between control and treated groups seems to have been due to a low incidence (42 %) in the control group rather than to treatment with the test material.

There were no statistically significant differences in the overall incidence of tumours, either benign or malignant, between the treated and control male rats. In the females there was a higher incidence of benign tumours, but this was no longer the case when the pituitary tumours were excluded and incidences of pituitary tumours do not seem to have been due to tumours.

Interstitial cell tumour of the testis was the only other individual tumour that occurred in treated rats with a frequency of statistical significance. Dunnington cite reports that such tumours are the most common testicular neoplasmin the rat. Control data from Dunnington et al.'s laboratory indicate an incidence in some studies as high as 10 % in Wistar rats, with much variation between groups. In this study there was an incidence of 5 % in the control animals, while in those fed 0.02 % test material there was an incidence of 23 % and in the group fed 0.5 % test material an incidence of 22 %. The incidence among the rats fed 0.1 % test material however was 3 % so there was no dose-response relationship.

All of the tumours were present in animals killed at the end of the study; none was found at earlier stages. The lack of any relationship between dosage and the number of tumours found or of any evidence for a shortening of the latent period suggested to Dunnington et al. that the distribution of these testicular tumours was more likely to be a reflection of variations in the normal incidence in rats than an effect of the test material, although the latter possibility cannot be ruled out entirely.

There was no dose-association pattern in the occurrence of other benign tumours in treated rats and all the types encountered were well documented in previous literature.

A number of malignant tumours occurred in treated animals but not in controls. However, reticulum-cell sarcoma, haemangiosarcoma, adrenal carcinoma, basel-cell carcinoma, endometrial sarcoma, spindle-cell sarcoma of the bladder and of the large intestine, an mammary adenocarcinoma have all been reported to arise spontaneously in the rat. Two of these types of tumour of particular interest to Dunnington et al: Lymphosacroma and reticulum cell sarcoma form a group of tumours that occur spontaneously in the lymphoretuclar system of ageing rats, and cite an incidence of 20 % that had been reported in the Furth strain of Wistar rat. In Dunnington's laboratory, there was an overall incidence of 3.3 % for males and 1.2 % for females among control Wistar animals. The overall incidences in the various groups were similar to this background figure and there was no evidence of any dose-relationship, particularly since none of these sarcomata were present in animals on the highest dose level. It seems likely therefore to Dunnington et al. that the incidence of lymphoreticular tumours recorded in the investigation was affected by the administration of the test material.

Vascular neoplasms formed the second group of tumours that occurred with relatively high frequency in the study. Malignancies of vascular origin were present in the lymph nodes, liver, kidney and uterus.

The overall incidence of tumours of vascular origin classified as malignant (haemangiosarcoma and haemangioendothelioma) was 1, 1, 1,0 in the control, 0.02 %, 0.1 % and 0.5 % dose males respectively, and 0, 1, 1, 2 in the females. These incidences were not statistically-significant and showed no overall dose relationship. Although these tumours were classified as malignant, doubt remains as to their exact nature because of a combination of local invasive properties and benign cytological features. This problem had been encountered with vascular tumours at other sites.

Although some of the benign tumours occurred with increased frequency in the treated animals, Dunnington et al. found that there was no conclusive evidence to link their development with treatment with the test material.
Relevance of carcinogenic effects / potential:
Although some of the benign tumours occurred with increased frequency in the treated animals, Dunnington et al. found that there was no conclusive evidence to link their development with treatment with the test material.
Conclusions:
Dunnington et al. did not find any cause for concern regarding potential carcinogenicity of the test material.
Endpoint conclusion
Endpoint conclusion:
no adverse effect observed
Dose descriptor:
NOAEL
175 mg/kg bw/day
Study duration:
chronic
Species:
rat

Carcinogenicity: via inhalation route

Endpoint conclusion
Endpoint conclusion:
no study available

Carcinogenicity: via dermal route

Endpoint conclusion
Endpoint conclusion:
no study available

Additional information

Dunnington et al. examined carcinogenicity in a 2 yr repeat oral toxicity study in the rat. There was no neoplastic treatment effect at 0.5 % (the highest dose administered), which was higher than the overall NOAEL of 0.1 % in diet. Using the conversion in the report, i..e from the NOAEL of 0.1 % to doses of 35 mg/kg bw in males and 60 mg/kg bw/d in females, this corresponds to average doses of 175 mg/kg body weight/day in males and 300 mg/kg body weight/day in females.


Justification for selection of carcinogenicity via oral route endpoint:
Only study available

Justification for classification or non-classification

According to Regulation (EC) No. 1907/2008, substances should be classified as carcinogenic if there is evidence of their carcinogenicity in animal or human studies. On the basis of the available evidence, the substance should not be classified as carcinogenic. The categories that can be ruled out are category 1B and category 2. However, because of the lack of human data, it is not possible to conclude definitively on category 1A, although based on screening principles, carcinogenicity is not of particular concern.