‘Substantial modification’ means any change to any aspect of the clinical trial which is made after notification of a decision referred to in Articles 8, 14, 19, 20 or 23 and which is likely to have a substantial impact on the safety or rights of the subjects or on the reliability and robustness of the data generated in the clinical trial. (EU) Nr. 536/2014 Art. 2 Abs. 2 (13)