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Carcinogenicity

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Description of key information

The carcinogenic potential of formamide was examined in 2-year oral gavage studies conducted with mice and rats. There was no evidence of carcinogenic activity of formamide in male and female rats. There was clear evidence of carcinogenic activity in male mice, based on increased incidences of liver hemangiosarcoma, and equivocal evidence of carcinogenic activity in female mice based on increased incidences of hepatocellular adenoma or carcinoma (combined).
Given the facts that carcinogenic activity was only seen in the male mouse, but not in rats or in the female mouse, and that formamide was negative in almost all genetic toxicity assays, it is concluded that the mode of action for the observed carcinogenicity is other than genetic toxicity.

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:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
other: GLP guideline study.
Reason / purpose:
reference to other study
Qualifier:
according to
Guideline:
OECD Guideline 451 (Carcinogenicity Studies)
GLP compliance:
yes
Species:
mouse
Strain:
B6C3F1
Sex:
male/female
Details on test animals and environmental conditions:
TEST ANIMALS
- Source: Taconic Laboratory Animals and Services (Germantown, NY), USA
- Age at study initiation: 7 - 8 weeks
- Housing: Caging: males singly, females in groups of 5
- Diet: ad libitum
- Water: ad libitum
- Acclimation period: 21 days before initiation of the studies


ENVIRONMENTAL CONDITIONS
- Temperature (°C): 72 +/-3°F
- Humidity (%): 50 +/-15%
- Air changes (per hr): 10/hour
- Photoperiod (hrs dark / hrs light): 12/12 hours

Route of administration:
oral: gavage
Vehicle:
other: deionized water
Details on exposure:
PREPARATION OF DOSING SOLUTIONS:
Mixing formamide with deionized water. Dose formaulations were stored at approximately 5°C in amber glass bottles for up to 50 days (Report, page 151).
Analytical verification of doses or concentrations:
yes
Details on analytical verification of doses or concentrations:
Periodic analyses of the dose formulations of formamide were conducted by the study laboratory using HPLC by system A ( detection; cf. report page 154). During the 2-week studies, the dose formulations were analyzed once; all five dose formulations for rats and mice were within 10% of the target concentrations (Table I3). Animal room samples of these dose formulations were also analyzed; all five animal room samples were within 10% of the target concentrations. During the 3-month studies, the dose formulations were analyzed at the beginning, midpoint, and end of the studies; animal room samples of these dose formulations were also analyzed (Table I4). All dose formulations analyzed for rats (15) and mice (15) were within 10% of the target concentrations; all 15 animal room samples for rats and mice were within 10% of the target concentrations. During the 2-year studies, the dose formulations were analyzed approximately every 3 months (Table I5). All dose formulations analyzed for rats (27) and mice (30) were within 10% of the target concentrations; all animal room samples for rats (12) and mice (12) were within 10% of the target concentrations.
Duration of treatment / exposure:
104 to 105 weeks
Frequency of treatment:
5 days per week
Remarks:
Doses / Concentrations:
0, 20, 40, and 80 mg/kg bw
Basis:
actual ingested
No. of animals per sex per dose:
50 per sex and dose
Control animals:
yes, concurrent vehicle
Details on study design:
- Dose selection rationale: dose levels were selected based on the results of preceding 2-week and 3-months studies
Positive control:
not required
Observations and examinations performed and frequency:
CAGE SIDE OBSERVATIONS: Yes
- Time schedule: twice daily

DETAILED CLINICAL OBSERVATIONS: Yes
- Time schedule: every four weeks

BODY WEIGHT: Yes
- Time schedule for examinations: weekly for teh first 13 weeks, at 4-week intervals thereafter and at the end of the study.

FOOD EFFICIENCY:
- 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

OPHTHALMOSCOPIC EXAMINATION: No

HAEMATOLOGY: No
- Time schedule for collection of blood:

CLINICAL CHEMISTRY: No

URINALYSIS: No

NEUROBEHAVIOURAL EXAMINATION: No
Sacrifice and pathology:
GROSS PATHOLOGY: Yes. All animals were necropsied.
HISTOPATHOLOGY: Yes. Complete histopathology was performed on all 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 mainstream bronchi), lymph nodes (mesenteric), mammary gland, nose, ovary, pancreas, parathyroid gland, pituitary gland, preputial gland, prostate gland, salivary gland, skin, spleen, stomach (forestomach and glandular) testis (with epididymis and seminal vesicle), thymus, thyroid gland, trachea, urinary bladder, and uterus.
Statistics:
The statistical analysis included:
Survival analysis: probability of survival was estimated according to Kaplan-Meyer (1958); dose-related effects on survival were analyzed using Cox's (1972) method.
Organ and body weight data: according to Dunnett (1955) and Williams (1971, 1972).
Clinical pathology, including hematology, clinical chemistry, sperm count and estrous cycle data: Shirley (1977), Dunn (1964), Jonckheere (1954).
Cf. report, pages 25-26, for more detail information.


Clinical signs:
no effects observed
Mortality:
no mortality observed
Body weight and weight changes:
effects observed, treatment-related
Ophthalmological findings:
not examined
Haematological findings:
not examined
Clinical biochemistry findings:
not examined
Urinalysis findings:
not examined
Behaviour (functional findings):
not examined
Organ weight findings including organ / body weight ratios:
not examined
Gross pathological findings:
no effects observed
Histopathological findings: non-neoplastic:
effects observed, treatment-related
Histopathological findings: neoplastic:
effects observed, treatment-related
Details on results:
Detail information is contained in the full study report which is attached to the study record pertaining to the rat carcinogenicity study.

CLINICAL SIGNS AND MORTALITY
No clinical findings were attributed to the administration of formamide.
Survival of all dosed groups of mice was similar to that of the vehicle controls (for details see below, and report, Figure 7; Tables 13 and 14).


BODY WEIGHT AND WEIGHT GAIN
Mean body weights of 80 mg/kg males were generally less than those of the vehicle controls throughout the study; mean body weights of 40 and 80 mg/kg females were generally less than those of the vehicle controls after weeks 13 and 6, respectively (for details see below, and report, Figure 8; Tables 13 and 14).


GROSS PATHOLOGY
No findings.

HISTOPATHOLOGY: NON-NEOPLASTIC
Testis: There were significant increases in the incidences of minimal to mild mineralization of the testicular arteries in 40 and 80 mg/kg males and the testicular tunic in 80 mg/kg males (see below, and report, Tables 16 and C4; Plates 4 through 6).
Spleen: In 80 mg/kg males, there was a significant increase in the incidence of splenic hematopoietic cell proliferation (se below, an dreport Tables 16 and C4).
Pancreas: There were significant decreases in the incidences of hyperplasia of the pancreatic islets in all dosed groups of males and in the incidence of splenic hematopoietic cell proliferation in 80 mg/kg females (see below, and report Tables 16, C4, and D4). The biological significance of the increases and decreases in these nonneoplastic lesions is uncertain. The increased incidence of splenic hematopoietic cell proliferation in males may be due to erythrocyte damage induced by the hepatic hemangiosarcomas that occurred in male mice.

HISTOPATHOLOGY: NEOPLASTIC
Liver:
Males: The incidences of hemangiosarcoma occurred with a positive trend in males, and the incidences were significantly increased at 40 and 80 mg/kg (see below, and report Tables 15 and C2). The incidences of hemangiosarcoma in all dosed groups of males exceeded the historical control ranges (all routes) (Tables 15 and C3). Microscopically, the hemangiosarcomas were composed of tortuous vascular spaces lined by plump, elongated spindle cells. They were often associated with thrombi and infarction or centrilobular necrosis in the surrounding parenchyma and adjacent liver lobes.
Hemangiosarcomas also occurred in the spleen (vehicle control, 2/50; 20 mg/kg, 2/50; 40 mg/kg, 2/50; 80 mg/kg, 3/50; Table C2), but the incidences did not increase in a dose-dependent manner; the vehicle control incidence was at the high end of the historical control ranges, and the incidence in the 80 mg/kg group only slightly exceeded the current ranges of NTP historical control values (Table C3).

The incidences of clear cell focus in 80 mg/kg males and fatty change in 40 and 80 mg/kg males were significantly decreased; the biological significance of these decreases is uncertain (Tables 15 and C4).

Females: The incidence of hepatocellular adenoma or carcinoma (combined) was significantly increased in 80 mg/kg females but was within the historical control ranges (Tables 15, D2, and D3). Microscopically, the hepatocellular adenomas were well-circumscribed lesions usually occupying an area greater than one liver lobule, usually lacking central veins and portal areas, and with distinct compression of adjacent parenchyma. The hepatocytes were well-differentiated and occurred in irregular plates (one to three layers thick). Mitotic figures and eosinophilic cytoplasmic inclusions were also characteristic features. Microscopically, the hepatocellular carcinomas
were large neoplasms that often showed solid or trabecular growth patterns (cords three or more cell layers thick) and cytological atypia.


Lung: In 80 mg/kg male mice, there was a significant decrease in the incidence of alveolar/bronchiolar adenoma; however, the vehicle control incidence is higher than the NTP historical control mean incidence for all routes of administration (Tables 16, C1, and C2). The biological significance of this decrease in pulmonary alveolar/bronchiolar adenoma is uncertain. The incidence of histiocytic cellular infiltration in the lung alveolus was significantly increased for 80 mg/kg males, but the biological significance of the increase is uncertain (Tables 16 and C4).


HISTORICAL CONTROL DATA
Report, appendices C and D

Relevance of carcinogenic effects / potential:
Overall, there was clear evidence of carcinogenic activity of formamide in male B6C3F1 mice based on increased incidences of hemangiosarcoma of the liver. There was equivocal evidence of carcinogenic activity of formamide in female B6C3F1 mice based on increased incidences of hepatocellular adenoma or carcinoma (combined).
Dose descriptor:
NOAEL
Effect level:
20 mg/kg bw/day (actual dose received)
Sex:
male
Basis for effect level:
other: incidence of neoplasms within historical range or not gaining statistical significance
Remarks on result:
other: Effect type: carcinogenicity (migrated information)
Dose descriptor:
NOAEL
Remarks:
equivocal
Effect level:
80 mg/kg bw/day (actual dose received)
Sex:
female
Basis for effect level:
other: incidence of neoplasms within historical range or not gaining statistical significance
Remarks on result:
other: Effect type: carcinogenicity (migrated information)
Dose descriptor:
LOAEL
Effect level:
40 mg/kg bw/day (actual dose received)
Sex:
male
Basis for effect level:
other: statistically significant increase of hemangiosarcoma of liver
Remarks on result:
other: Effect type: carcinogenicity (migrated information)

Table 1: Mortality: Survival of rats in the 2-Year study

   Control  20 mg/kg/d  40 mg/kg/d  80 mg/kg/d    
 Male            
 Animal initially  50  50  50  50    
 Moribund  4  8  6  14    
 Natural deaths  7  0  8  3    
 Animals surviving to study termination  39  42  36  33    
 Percent probability of survival            
 at end of study (a)  78  84  72  66    
 Mean survival (days) (b)  698  708  690  695    
 Survival analysis (c)  0.101 0.586   0.680  0.290    
 Female            
 Animal initially  50  50  50  50    
 Moribund  7  8  8  8    
 Natural deaths  5  3  10  39    
Animals surviving to study termination  38  39  31  39    
 Percent probability of survival            
 at end of study  76  78  63  78    
 Mean survival (days)  692  700  670  711    
 Survival analysis  0.977N  0.951N  0.275  0.886N    

(a) = Kaplan-Meier determinations

(b) = mean of all deaths (uncensored, censored, and terminal sacrifice)

(c) = the result of the life table trend test (Tarone, 1975) is in the vehicle control column, and the results of the life table pairwise comparisons (Cox, 1972) with the vehicle controls are in the dosed group columns. A negative trend or lower mortality in a dose group

is indicated by N.

Table 2: Body weights:

Mean body weights of 80 mg/kg males were generally less than those of the vehicle controls throughout the study. Mean body weights of 40 and 80 mg/kg females were generally less than those of the vehicle controls after weeks 12 and 52, respectively.

Average weight data:

 Week on study  Control  20 mg/kg/d  40 mg/kg/d  80 mg/kg/d  
   [g]  [% of control]         
 Males          
 1 - 13  29.9  99  96  93  
 14 - 52  47.1  99  96  94  
 53 - 104  51.7  100  98  92  
 Females          
 1 - 13  24.4  98  97  95  
 14 - 52  44.4  98  93  86  
 53 - 104  59.4  98  88  87  

Pathology

Statistically significant or biologically noteworthy changes in the incidences of neoplasms and nonneoplastic lesions of the liver, testes, lung, spleen, and pancreatic islets were as follows:

(1) Liver:

Males: the incidences of hemangiosarcoma occurred with a positive trend in males, and the incidences were significantly increased at 40 and 80 mg/kg (P</=0.05). The incidences of hemangiosarcoma in all male dosed groups exceeded the historical range in controls (all routes).

Microscopically, the hemangiosarcomas were composed of tortuous vascular spaces lined by plump, elongated spindle cells. They were often associated with thrombi and infarction or centrilobular necrosis in the surrounding parenchyma and adjacent liver lobes. Hemangiosarcomas also occurred in the spleen (vehicle control, 2/50; 20 mg/kg, 2/50; 40 mg/kg, 2/50; 80 mg/kg, 3/50), but the incidences did not increase in a dose-dependent manner, the vehicle control incidence was at the high end of the historical control range, and the incidence in the 80 mg/kg group only slightly exceeded the current range of NTP historical control values.

Table 3: Neoplasms of the liver in mice

   Control  20 mg/kg/d  40 mg/kg/d  80 mg/kg/d    
 Male            
 Numer examined  50  50  50  50    
 Clear cell focus (a)  29  27  21  8**    
 Fatty Change (b)  31 (1.6)  25 (1.4)  15**(1.3)  1** (1.0)    
 Hemangiosarcoma (c)            
 Overall rate (d)  1/50 (2%)  5/50 (10%)  7/50 (14%)  8/50 (16%)    
 Adjusted rate (e)  2.2%  10.6%  15.2% 17.5%     
 Terminal rate (f)  1/39 (3%)  4/42 (10%)  4/36 (11%)  3/33 (9%)    
 First incidence (days)  728 (T)  655  449  635    
 Poly-3 test (g)  P=0.018  P=0.110  P=0.032  P=0.016    
           
   Female            
Number examined  50   50  50  50    
 Hepatocellular Adenoma            
 Multiple  2  3  2    
 Hepatocellular Adenoma (includes multiple) (h)        
 Overall rate  6/50 (12%)  12/50 (24%)  13/50 (26%)  12/50 (24%)    
 Adjusted rate  13.2 %  26.2 %  29.4 %  25.4 %    
 Terminal rate  3/38 (8%)  11/39 (28%)  9/31 (29%)  11/39 (28%)    
 First incidence (days)  653  674  407  694    
 Poly-3 test  P=0.149  P=0.096  P=0.051  P=0.109    
 Hepatocellular Carcinoma            
 Multiple  0  1  0  1    
 Hepatocellular Carcinoma            
 (includes multiple) (i)  4  4  0  6    
 Hepatocellular Adenoma or Carcinoma (j)            
 Overall rate  9/50 (18%)  15/50 (30%)  13/50 (26%)  18/50 (36%)    
 Adjusted rate  19.8 %  32.6 %  29.4 % 37.8 %     
 Terminal rate  6/38 (16%)  13/39 (33%)  9/31 (29%)  14/39 (36%)    
 First incidence (days)  653  665  407  657    
 Poly-3 test  P=0.056  P=0.124  P=0.209  P=0.044    

** Significantly different (P=0.01) from the vehicle control group by the Poly-3 test

(T)Terminal sacrifice

(a) Number of animals with lesion

(b) Average severity grade of lesions in affected animals: 1=minimal, 2=mild, 3=moderate, 4=marked

(c) Historical incidence for 2-year water gavage studies with vehicle controls given NTP-2000 diet (mean ± standard deviation):

gavage: 6/200 (3.0% ± 1.2%), range 2%-4%; all routes: 33/1,496 (2.3% ± 1.6%), range 0%-8%

(d) Number of animals with neoplasm per number of animals with liver examined microscopically

(e) Poly-3 estimated neoplasm incidence after adjustment for intercurrent mortality

(f) Observed incidence at terminal kill

(g) Beneath the vehicle control incidence is the P value associated with the trend test. Beneath the dosed group incidence is the P value

corresponding to pairwise comparisons between the vehicle controls and that dosed group. The Poly-3 test accounts for differential

mortality in animals that do not reach terminal sacrifice.

(h) Historical incidence for 2-year water gavage studies: gavage: 41/200 (20.5% ± 8.7%), range 12%-28%; all routes: 402/1,593 (25.8% ±

15.8%), range 2%-62%

(i) Historical incidence for 2-year water gavage studies: gavage: 16/200 (8.0% ± 4.3%), range 4%-14%; all routes: 159/1,593 (10.2% ±

6.6%), range 0%-28%

(j) Historical incidence for 2-year water gavage studies: gavage: 53/200 (26.5% ± 10.0%), range 18%-40%; all routes: 505/1,593 (32.4% ±

17.5%), range 8%-64%

Females: The incidence of hepatocellular adenoma or carcinoma (combined) was significantly increased in 80 mg/kg females but was within the historical control range. Microscopically, the hepatocellular adenomas were well-circumscribed lesions usually occupying an area greater

than one liver lobule, usually lacking central veins and portal areas, and with distinct compression of adjacent parenchyma. The hepatocytes were well differentiated and occurred in irregular plates (one to three layers thick). Mitotic figures and eosinophilic cytoplasmic inclusions were also characteristic features. Microscopically, the hepatocellular carcinomas were large neoplasms that often showed solid or trabecular growth patterns (cords three or more cell layers thick) and cytological atypia.

(2) Testes: There were significant increases in the incidences of minimal to mild mineralization of the testicular arteries and testicular tunic in 80 mg/kg males.

(3) Lung: In 80 mg/kg male mice, there was a significant decrease in the incidence of alveolar/bronchiolar adenoma; however, the vehicle control incidence is higher than the NTP historical control mean incidence for all routes of administration. The biological significance of this decrease in pulmonary alveolar/bronchiolar adenoma is uncertain. The incidence of histiocytic cellular infiltration in the lung alveolus of 80 mg/kg males was significantly increased, but the biological significance of the increase is uncertain.

(4) Other organs: In 80 mg/kg males, there was a significant increase in the incidence of splenic hematopoietic cell proliferation. There were significant decreases in the incidences of hyperplasia of the pancreatic islets in all male dosed groups and in the incidence of splenic hemato- poietic cell proliferation in 80 mg/kg females. The biological significance of the increases and decreases in these nonneoplastic lesions is uncertain. The increased incidence of splenic hematopoietic cell proliferation in males may be due to erythrocyte damage induced by the hepatic hemangiosarcomas that occurred in male mice.

Table 4: Selected neoplasms and non-neoplastic lesions in mice

   Control  20 mg/kg/d  40 mg/kg/d  80 mg/kg/d      
 Male              
 Testes (a)  50  50  50  50      
 Artery, Mineralization  0  2 (1.0)(c)  5* (1.4)  35** (1.6)      
 Tunic, Mineralization  1 (1.0)  0  5 (1.0)  27 (1.8)      
 Lung  50  50  50  50      
 Alveolus, Infiltration; Cellular              
 Histiocyte  1 (1.0)  0  1 (2.0)  8* (1.5)      
Alveolus/bronchiolar Adenoma (d) (includes multiple)  10  4  7  1**      
 Spleen  50  50  50  50      
 Hematopoietic Cell              
 Proliferation  14 (2.1)  14 (2.2) 20 (1.9)   28** (2.0)      
 Islets, Pancreatic  50  50  50  50      
 Hyperplasia  35 (1.4)  24* (1.3) 24* (1.3)   9** (1.3)      
 Female              
Spleen   50  49  49  50      
 Hematopoietic Cell              
 Proliferation  17 (2.6)  17 (2.2)  15 (2.7)  8* 2.8)      

* Significantly different (P=0.05) from the vehicle control group by the Poly-3 test (2-year study); ** P=0.01

(a) Number of animals with tissue examined microscopically

(b) Number of animals with lesion

(c) Average severity grade of lesions in affected animals: 1=minimal, 2=mild, 3=moderate, 4=marked

(d) Historical incidence for 2-year water gavage studies with vehicle controls given NTP-2000 diet (mean ± standard deviation): gavage:

40/200 (20.0% ± 0.0%), range 20%; all routes: 263/1,498 (17.9% ± 6.1%), range 6%-28%

Conclusions:
Formamide was carcinogenic in male B6C3F1 mice based on increased incidences of hemangiosarcoma of the liver in a valid 2-year oral gavage study.
Executive summary:

The carcinogenic potential of formamide (0, 20, 40, and 80 mg/kg bw/day, oral gavage) was examined in a GLP study using male and female B6C3F1mice (50 animals per sex and dose) that was conducted in accordance with the OECD guideline No. 451. The dose level selection was based on the results of preceding 2-week and 3-months studies.

Survival of the male and female mice receiving 20, 40, and 80 mg/kg bw/day in this 2-year study was comparable to that of the control animals. Mean body weights of 80 mg/kg males were generally less than those of the vehicle controls throughout most of the 2-year study. Mean body weights of mice at 40 and 80 mg/kg were less than those of the vehicle controls during the second year of the study and at termination.

There was an increased occurrence of liver hemangiosarcomas in all three groups of male mice receiving formamide (statistically significant at 40 and 80 mg/kg bw/day), and a less pronounced increase in hepatocellular adenomas or carcinomas of the liver in female mice which, however, was in the range of historical controls and lacked a dose relationship. In male mice receiving 80 mg/kg of formamide, there was also mineralization of the testicular arteries and tunic and hematopoietic cell proliferation of the spleen.

It was concluded that there was clear evidence of carcinogenic activity of formamide in male B6C3F1 mice based on increased incidences of hemangiosarcoma of the liver. There was equivocal evidence of carcinogenic activity of formamide in female B6C3F1 mice based on increased incidences of hepatocellular adenoma or carcinoma (combined) (NTP, 2008).

 

Endpoint conclusion
Dose descriptor:
NOAEL
20 mg/kg bw/day
Study duration:
chronic
Species:
mouse
Quality of whole database:
Reliable without restrictions. The study was conducted according to OECD guidelines and under GLP conditions.
System:
hepatobiliary
Organ:
liver

Additional information

In the standard 2-year carcinogenicity studies with rats and mice, induced tumours were observed in only one organ (liver), one sex (male) and one species (mice), as detailed below. Based on the weight of evidence of the available genotoxicity data, formamide is not considered to be mutagenic. Although the mode of induction of tumours has not been developed and elucidated, the tumours observed in the experimental animals are unlikely to have resulted from direct interaction with genetic (cf. OECD (2007), Environmental Canada (2009) in Section 13). Therefore, a threshold dose may be assumed below which there is no or minimal risk. The NOAEL or LOAEL value obtained in the mouse study (20 and 40 mg/kg bw/day, respectively) may be used for the assessment of exposure related risks for humans.

 

2 - year gavage study in rats

The carcinogenic potential of formamide (0, 20, 40, and 80 mg/kg bw/day, oral gavage) was examined in a GLP study using male and female F 344 rats (50 animals per sex and dose) that was conducted in accordance with the OECD guideline No. 451 (Key 1 study). The dose level selection was based on the results of preceding 2-week and 3-months studies.

Survival of male and female rats receiving 20, 40, and 80 mg/kg bw/day in this 2-year study was comparable to that of the control animals. Mean body weights of 80 mg/kg male rats were less than those of the vehicle controls throughout most of the 2-year study. Mean body weights of 40 and 80 mg/kg female rats were less than those of the vehicle controls during the second year of the study.

There were no significant changes in the incidences of neoplasms in rats associated with administration of formamide. The incidences of pituitary gland (pars distalis) adenoma were increased in dosed male rats; however, the vehicle control incidence was lower than the mean NTP historical control incidence for all routes of administration, and the incidences of pituitary gland (pars distalis) adenoma or carcinoma (combined) in female rats decreased with dose. Therefore, the biological significance of the increased incidences of pituitary gland adenoma in male rats is uncertain, and the increases are not considered treatment related.

 

Overall, there was no evidence of carcinogenic activity of formamide in male and female rats.

 

2 - year gavage study in mice

The carcinogenic potential of formamide (0, 20, 40, and 80 mg/kg bw/day, oral gavage) was examined in a GLP study using male and female B6C3F1mice (50 animals per sex and dose) that was conducted in accordance with the OECD guideline No. 451 (Key 2 study). The dose level selection was based on the results of preceding 2-week and 3-months studies.

Survival of the male and female mice receiving 20, 40, and 80 mg/kg bw/day in this 2-year study was comparable to that of the control animals. Mean body weights of 80 mg/kg males were generally less than those of the vehicle controls throughout most of the 2-year study. Mean body weights of mice at 40 and 80 mg/kg were less than those of the vehicle controls during the second year of the study and at termination.

There was an increased occurrence of liver hemangiosarcomas in all three groups of male mice receiving formamide (statistically significant at 40 and 80 mg/kg bw/day) and a less pronounced increase in hepatocellular adenomas or carcinomas of the liver in female mice which, however, was in the range of historical controls and lacked a dose relationship. In male mice receiving 80 mg/kg of formamide, there was also mineralization of the testicular arteries and tunic and hematopoietic cell proliferation of the spleen. The NOAEL was 20 mg/kg bw/day for male and 80 mg/kg bw/day for female mice.

It was concluded that there was clear evidence of carcinogenic activity of formamide in male B6C3F1 mice based on increased incidences of hemangiosarcoma of the liver. There was equivocal evidence of carcinogenic activity of formamide in female B6C3F1 mice based on increased incidences of hepatocellular adenoma or carcinoma (combined).

Overall conclusion:

The evidence of carcinogenicity is supposed to be sufficient for classification, although clear evidence was only seen in a single species, and only in one sex. Equivocal evidence was seen in female mice (increased incidence of combined hepatocellular adenoma and carcinoma). No carcinogenic activity was seen in male or female rats. However, positive results of from the available in vitro cell transformation tests support the classification.

Further in vitro and in vivo mutagenicity data are negative: Ames test (NTP 2008), CTA in rat embryo cells (Freeman 1973), Dros.SLRL test/OECD477 (NTP 2008), DLA/OECD478 (BASF 1974) and an in vivo micronucleus test after 3 month of oral administration up to 160 mg/kg formamide (NTP 2008). However, an in vivo micronucleus test showed increased frequencies of micronuclei in bone marrow erythrocytes 48 h after a single i.p. administration of >= 900 mg/kg formamide (BASF 2001).The registrants consider that this positive result is a result of secondary toxicity but does not indicate a genotoxic mode of action, due to the effect of formamide on the hematopoietic system, which was also observed in several repeated dose toxicity studies (e.g. 2- week range finder and 90-d gavage study in rat and mouse: NTP 2008; 28-d gavage study in rat: BASF 1978). Therefore, the registered substance is classified with STOT RE 2 (target organ: blood, oral).

The registered substance is therefore considered to be a suspected carcinogen but lacking genotoxic mode of action. The mode of action is at present still unclear.

Justification for classification or non-classification

Considering the results of the available carcinogenicity studies, the registered substance is classified as a Category 2 (H351) suspected carcinogen, in accordance with the provisions of the Regulation (EC) No 1272/2008 (CLP), No. 3.6, on the basis of clear evidence of carcinogenic activity (hemangiosarcoma) in male B6C3F1 mice.