RET and neoplasm: Out of the 760 samples for which the RET-FISH analysis yielded an interpretable result, 32 (4%) were positive by FISH (≥15% of tumor cells with separated 5′ and 3′ signals or isolated 3′ signals or both) and 728 / 760 (96%) were negative (<15% positive tumor cells) (Fig. 3 and Table 3).