Real-time quantitative PCR measurement of thyroglobulin mRNA in peripheral blood of thyroid cancer patients and healthy subjects.

Follow-up of recurrent differentiated thyroid carcinoma involves the measurement of serum thyroglobulin (Tg). However, Tg autoantibodies are present in a high proportion of thyroid carcinoma patients (up to 25%) and these can interfere with the Tg immunoassays. To overcome this obstacle, investigators have used real-time quantitative reverse transcriptase polymerase chain reaction (RT-PCR) to measure Tg mRNA in the blood of patients with differentiated thyroid cancer, with varying degrees of success. In the present study, we demonstrate the first reported use of the PAXgene Blood RNA collection tube and extraction kit method for the preparation of RT-PCR-quality RNA with subsequent deployment of the latter in the development of a specific, sensitive, and reproducible Taqman assay for the detection and quantification of thyroglobulin mRNA. Beta-actin mRNA was also assayed and results are expressed as a ratio of Tg to beta-actin mRNA. The intra-assay coefficient of variations (CVs) for Tg and beta-actin mRNA assay were 27.7% and 25.4%, respectively. Inter-assay CVs were 20.8% and 28.8%, respectively, for the two assays. Tg mRNA was detected in all cancer subjects (n = 42) and healthy individuals (n = 20). Tg mRNA was significantly higher in cancer patients than in the healthy subjects (0.00169 +/- 0.00013 vs. 0.00051 +/- 0.00015; P<0.0001). Fourteen cancer patients had detectable levels of serum Tg, and Tg mRNA levels tended to be higher in these than in cancer subjects with undetectable serum Tg (0.00188 +/- 0.00021 vs. 0.00157 +/- 0.000178; P = 0.08). Circulatory Tg mRNA measurement may serve a useful role in the assessment of thyroid cancer.