During the meeting of the Member State Committee (MSC), held in June 2022, the request to investigate chromosomal aberrations in the decisions for in vitro and in vivo testing has been discussed.

The meeting brought some changes, summarized down below:

  • the choice between the in vitro chromosomal aberration (CA) test and the in vitro micronucleus (MN) test for REACH Annex VIII data requirement has been removed. Solely the in vitro MN test is now required;
  • request the combined in vivo comet assay and MN test for substances with a chromosomal aberration concern identified in vitro, except for substances showing only aneugenic effects, for which an in vivo MN test must be requested. The MSC considered that substance-specific reasons could justify deviating from this generic principle;
  • centromere staining must be performed when the number of micronuclei is increased in the MN test, to investigate the mode of action (clastogenic and/or aneugenic) of the substance; and
  • ECHA will require the appropriate investigation of target tissue exposure when requesting an in vivo MN assay, alone or combined with a comet assay.

From September 2022, all new dossier evaluation draft decisions texts will follow the agreed approaches for in vitro and in vivo testing.

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