RET and neoplasm: Regarding the positivity thresholds applied, in the study by Michels et al.,62 two different positivity thresholds (either 15% or 20%) were used by the two centers participating in the study, and no differences were found, as the 22 RET-FISH positive cases were all found to have more than 20% tumor cells with the ZytoVision RET break-apart probe, and the mean percentage of positive cells (fraction of RET rearranged cells) in the positive cases was 47.9%, largely above the two positivity thresholds.