PAX8 and thyroid gland undifferentiated (anaplastic) carcinoma: In the most extensive molecular studies performed so far, gene fusions have been detected in 11 of 52 cases of poorly differentiated thyroid carcinoma (RET rearrangement in 5 cases, ALK rearrangement in 3 cases, PAX8/PPARG gene fusion in 3 cases) [15] and in 5 of 107 cases of anaplastic thyroid carcinoma (RET rearrangement in 2 cases, NTRK rearrangement in 3 cases) [28].