Technical Report 130

Step VI: Identification of uncertainties

The major uncertainties will have been addressed in the evaluation of the evidence in Step III and Step IV. Therefore, the specific guidance presented in Step VI refers back to these Steps. Uncertainties are likely to arise when the conclusion has been for insufficient evidence in either Step III or Step IV. For Level 4 and 5 studies (Step III), uncertainty mostly arises from the complexity of the studies and because of the interference of potentially endocrine and non-endocrine mechanisms. There are only few apical endpoints which are unambiguously indicative of an endocrine MoA. This highlights the importance of exploring the entire toxicity profile of a substance, and not only data pointing toward a potential endocrine MoA.6

There are 3 major sources of uncertainty:

  • The quality of data: Poor quality data (from ToxR Tool Reliability-Category 3 (and 4) studies and assays) from the data quality evaluation in Step II.
  • The equivocality of data: On occasion, it is difficult to draw conclusions from the data e.g. because the dose-response curve does not follow a consistent pattern of increasing effects with dose. Usually, equivocality of data can be resolved by reference to other studies. If no other studies are available, then it would be reasonable to generate more data. If other studies are available and they also show equivocal data, then there is no reason to generate more data.
  • The lack of data: There may be evidence of endocrine activity in one set of data but no data available from one of the other necessary sets of data (e.g. evidence from Level 2 in vitro assays, but no Level 3 in vivo assays or Level 4 and 5 in vivo studies). In this situation, it would be reasonable to generate further complementary data.