Quantitative reverse transcription-polymerase chain reaction of circulating thyroglobulin messenger ribonueleic acid for monitoring patients with thyroid carcinoma

Patients with thyroid cancer are monitored for disease recurrence by measurement of serum thyroglobulin (Tg) and iodine-131 (¹³¹I) scanning. To enhance sensitivity and to circumvent antibodies that interfere with Tg immunoassays, we have developed RT-PCR assays that detect circulating thyroid messenger Rna (mRNA) transcripts. We now report results using a sensitive quantitative Tg mRNA assay (Taqman; ABI, Foster City, CA) in comparison with immunoassay in patients previously treated for thyroid cancer. We evaluated 107 patients: 84 during T₄ therapy, 14 after T₄ withdrawal, and 9 at both time points. All patients had near-total thyroidectomy, and 92% received postoperative ¹³¹I. Serum TSH, Tg protein, and Tg mRNA were measured. Patients were grouped based on most recent ¹³¹I scan or pathologically confirmed disease as having no detectable thyroid tissue (n = 33), thyroid bed uptake (n = 37), cervical/regional adenopathy (n = 21), or distant metastases (n = 16). During T₄ therapy, median (range) Tg mRNA values (pg Tg Eq/μg thyroid RNA) for the groups were 1.5 (0-26.8), 9.4 (0.5-90.0), 15.4 (0.2-92), and 12.4 (1.9-16.6), respectively. Using a value of 3 pg Tg Eq/μg thyroid RNA as cut-point, Tg mRNA was positive in 38% of patients with no uptake, 75% with thyroid bed uptake, 84% with cervical/regional disease, and 94% with distant metastases. The median Tg mRNA value for patients with no uptake was lower than the median values for patients with thyroid bed uptake (P = 0.009) or with detectable thyroid tissue at any site (P = 0.010). Patients with negative ¹³¹I whole body scans were also less likely to have detectable Tg mRNA levels than were patients with thyroid bed uptake (P < 0.001) or any detectable thyroid tissue at any location (P < 0.001). Similar differences between these groups were seen after T₄ withdrawal and for the 23 patients with circulating anti-Tg antibodies, when analyzed separately. Eight of the nine patients studied with low and high TSH concentrations displayed greater amounts of circulating Tg mRNA after T₄ withdrawal. In three patients followed prospectively, the amount Tg mRNA correlated with the presence and absence of cervical metastases. In conclusion, we have demonstrated that a quantitative Tg mRNA assay can identify thyroid cancer patients with recurrent or residual thyroid tissue with greater sensitivity and similar specificity to Tg immunoassay during T₄ therapy. The assay was unaffected by anti-Tg antibodies, responded to TSH-stimulation, and was reduced after surgical removal of metastases. These data suggest that this quantitative Tg mRNA assay may be a sensitive marker of tumor recurrence or response to therapy, particularly in patients with anti-Tg antibodies.