This method assesses the activation of TRβ using proprietary TRβ CALUX® cells which originated from a human osteoblastic osteosarcoma U2OS line. These cells express a functioning human TRβ coupled with a luciferase reporter gene. Test items with an agonist or antagonist effect on TR activity can be detected and an increase or decrease of TR signalling results in corresponding changes in the expression of luciferase activity that can be measured with a luminometer. The gene discussed is TXNRD2; the disease is osteosarcoma.