Strontium hydroxide

Carcinogenicity

Description of key information

Supporting data on Strontium ranelate, Strontium chloride and Strontium nitrate show that strontium is not expected to have a mutagen or a carcinogen potential. 

Key value for chemical safety assessment

Carcinogenicity: via oral route

Endpoint conclusion

Endpoint conclusion:

no adverse effect observed

Justification for classification or non-classification

An indirect effect of strontium through activation of thyrocalcitonin production was regarded as unlikely by the authors of the study, since no parafollicular cell hyperplasia was noticed and no effects on CA serum levels were found. In addition, the effects of Sr on thyroid function was discussed in the context of a scientific discussion paper of the EMEA on strontium ranelate, because in the carcinogenicity study in rats an increased incidence of C-cell carcinoma in thyroids of male rats was seen, but this effect was not clearly dose-related and was found to be within the control range in other studies with the strain of rats used. Furthermore, no increased incidence of C-cell hyperplasia or adenoma was seen in the carcinogenicity study rats, and it is also mentioned in the discussion paper that no increase in thyroid C-cell proliferative lesions or in circulating calcitonin levels were found in a 52-week toxicity study in rats. Therefore, it can be concluded that based on the available animal data strontium does not have the potential to produce significant toxicity, or to be harmful to humans, following repeated exposure at low or moderate exposure concentrations relevant for classification.

Additional information

According to the EMEA report 2005, the results of a 105 weeks carcinogenicity in male and female rats, indicate some increased incidences of C-cell carcinoma in thyroids of male rats in the low (LD) and high dose (HD) groups. It is stated that it cannot completely be excluded that a subtle increase in plasma cation levels may have, in some individual rats, affected the progress on of thyroid C-cell hyperplasia/adenoma to carcinoma. However, taking the totality of the data into account, there is no clear evidence that the finding of increased incidences of C-cell carcinoma in LD and HD males in the main carcinogenicity study in the rat are related to strontium ranelate treatment. Moreover, there are some differences between human and rat with respect to calcitonin regulation, such as the age-related increased increase in calcitonin in rats, whereas the opposite occurs with increasing age in humans, which indicate that the tumour findings are of minor clinical relevance. In addition, the incidence of C-cell tumours was not increased in female rats and in male and female mice, and male F344 rats treated over 52 weeks with doses as in the carcinogenicity studies had no increase in thyroid C-cell proliferative lesions.

There is an absence of any published evidence on the formation of tumours in humans after exposure to stable strontium compounds. Information is available on the action of strontium in in-vivo and in-vitro screening systems for the prediction of mutagenicity or carcinogenicity of metal salts. The DNA synthesis in nuclear epithelia of kidney and liver was not inhibited by intra-peritoneal injection of strontium nitrate to mice (Amlacher, 1983). Investigations in an in-vitro screening system showed that strontium chloride did not affect the accuracy of the DNA synthesis (Sirover, 1976).