Analysis of Tg transcripts by real-time RT-PCR in the blood of thyroid cancer patients

Serum Tg (sTg) assays are sometimes unsatisfactory for monitoring thyroid cancer because interference caused by anti-Tg antibodies may reduce the sensitivity of the tests during thyroid hormone therapy. We have therefore developed a complementary method using real-bane quantitative RT-PCR based on the amplification of Tg mRNA. Two different pairs of primers were used for the determination of the frequency of one of the variants of the alternative splicing of Tg mRNA. The frequency of this variant was as high in patients (n=40) as in controls (n=30), accounting for about 33% of the total Tg mRNA. Using appropriate primers, we observed that Tg mRNA values in controls varied according to the volume of thyroid tissue and the TSH concentration. The Tg mRNA values allowed the definition of a positive cutoff point at 1 pg/mug total RNA. This cutoff point, tested on the group of patients treated for thyroid cancer, produced fewer false negative results than those obtained with sTg assays. The standardized, highly sensitive real-time RT-PCR technique may therefore prove useful as a complement to sTg assays, particularly for patients with recurrent thyroid cancer receiving T-4 therapy.