NKX2-5 and cancer: On the other hand, even though NKX2.5 was described to be transiently expressed only during thyroid organogenesis, until embryonic day 11.5 in mouse 2, normal human thyroid tissue, adjacent to papillary thyroid carcinoma, showed a marked nuclear staining for this transcription factor (Fig. 1e and f), suggesting that NKX2.5 might be re-expressed later in life or that the proximity to cancer environment had an impact on the pattern of expression of neighbor cells.