Molecular detection of thyroglobulin mRNA transcripts in peripheral blood of patients with thyroid disease by RT-PCR

The sensitive detection of circulating tumour cells in patients with differ entiated thyroid cancer may precede the detection of relapse by other diagn ostic studies - such as serum thyroglobulin - and thus may have important t herapeutic and prognostic implications. We performed reverse transcription- polymerase chain reaction (RT-PCR) on blood samples from patients diagnosed with thyroid disease using two different RT-PCR sensitivities. Additionall y, tissue specificity of TG mRNA-expression was determined using RNA extrac ts from 27 different human tissues. The lower limit of detection was 50-100 TG mRNA producing cells/ml blood using a 'normal' RT-PCR sensitivity and 1 0-20 cells/ml blood using a 'high' sensitivity. With the normal sensitivity TG mRNA was detected in 9/13 patients with thyroid cancer and metastasis, 63/137 patients with a history of thyroid cancer and no metastasis, 21/85 w ith non-malignant thyroid disease and 9/50 controls. With the high sensitiv ity TG mRNA was detected in 11/13 patients with thyroid cancer and metastas is, 111/137 patients with a history of thyroid cancer and no metastasis, 61 /85 with non-malignant thyroid disease and 41/50 controls. Interestingly, u sing the normal RT-PCR sensitivity TG mRNA transcripts are specific for thy roid tissue and detectable in the peripheral blood of controls and patients with thyroid disease. which correlates with a diagnosis of metastasized th yroid cancer. However, with a high RT-PCR sensitivity, TG mRNA expression w as found not to be specific for thyroid tissue and was not correlated with a diagnosis of thyroid cancer in patients. As a consequence, to date TG mRN A detected by RT-PCR in the peripheral blood cannot be recommended as a tum our marker superior to TG serum-level. (C) 2000 Cancer Research Campaign.