High prevalence of RET/PTC rearrangements in Ukrainian and Belarussian post-Chernobyl thyroid papillary carcinomas: a strong correlation between RET/PTC3 and the solid-follicular variant.

A sharp increase in the incidence of pediatric thyroid papillary cancer was documented after the Chernobyl power plant explosion. An increased prevalence of rearrangements of the RET protooncogene (RET/PTC rearrangements) has been reported in Belarussian post-Chernobyl papillary carcinomas arising between 1990 and 1995. We analyzed 67 post-Chernobyl pediatric papillary carcinomas arising in 1995-1997 for RET/PTC activation: 28 were from Ukraine and 39 were from Belarus. The study, conducted by a combined immunohistochemistry and RT-PCR approach, demonstrated a high frequency (60.7\% of the Ukrainian and 51.3\% of the Belarussian cases) of RET/PTC activation. A strong correlation was observed between the solid-follicular subtype of papillary carcinoma and the RET/PTC3 isoform: 19 of the 24 RET/PTC-positive solid-follicular carcinomas harbored a RET/PTC3 rearrangement, whereas only 5 had a RET/PTC1 rearrangement. Taken together these results support the concept that RET/PTC activation plays a central role in the pathogenesis of thyroid papillary carcinomas in both Ukraine and Belarus after the Chernobyl accident.